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Thinset Decoded: Which Thinset to use | Infographic

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Thinset Decoded Part 2:  Which is the Best Thinset to use for…

There are too many thinsets. How are you keep supposed to keep track of them all?

Besides, all you really need to know is which is the best thinset to use for your project without screwing it up. A quick look at Lowes.com currently shows 19 different kinds of thinset mortar. That’s not including the “premixed” variety (hint: don’t bother). So this is my attempt at solving this problem.

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The Infographic

My first post discusses some of the technical terms, like modified and unmodified, medium bed and LFT.

But, I ended up scrapping my idea for this post because it was simply too technical to explain by typing it out in paragraphs. It would have been a very tedious post to read through. Then came my idea of an infographic.

Thinset Decoded: A buyers guide to purchasing the right tile adhesive

The infographic is more flowchart than infographic but I’m hoping it will do a better job. It is simplified and it won’t answer every question that you have.

There are still going to be gaps and there’s still going to be questions. Some of these things I will answer below. The others you’ll have to ask in the comments.

Down at the bottom are specific products. The products are all from Mapei, Custom Building Products (CBP), and Laticrete. I’ve chosen these three because they are the three brands because of my familiarty with them but also because these brands are the easiest for the DIY’er to get a hold of.

There’s also Ditraset from Bostik which isn’t as easy to get for DIY’ers but is a great product for installing with Schluter products.

Also, in the chart, I’ve put an asterisk next to the best thinset choices in different brands (in my opinion).

Take a look at the chart and I’ll add some more details below:

best thinset to use infographic
* Recommended Thinsets

Specific applications:

Below are some more details about which thinset to use for different applications. In no particular order:

Glass Tile: For glass tile, it can be a bit of a challenge to get the mortar to grab. They make specific glass tile thinset’s which I recommend you use. My favorite is Laticrete’s Glass Tile Adhesive.

But the ones from Mapei and Custom Building Products work well also. Sometimes the glass tile manufacturer will have specific instructions on which thinset to use. It’s a good idea to read the instructions.

Large Tiles: This includes the ever popular wood grain plank tiles. This category went from being called Medium Bed Mortar, to LFT (Large Format Tile), and is now officially called  Large and Heavy Tiles (LHT). So when you go to the store you may see any of these terms.

What’s a large tile? One size is 15 inches or longer. 12×24’s are large tiles. 6×24’s are large tile. 18×18’s are large tiles.

You need to get the best thinset for these and it needs to say something about “Large Tiles” on it.

More tips for installing wood look tile flooring

ANSI ratings:  The mortars get tested and need to perform to certain levels. That’s where these ratings come in. Tiles that are outside in harsh conditions need to have a much stronger thinset than ones inside.

ANSI stands for American National Standards Specifications for the Installation of Ceramic Tile. Now you know why we use the term ANSI.

Exterior Applications: If you’re installing tile outside you need to be very careful which thinset you use. The thinset should cost you north of $40/ bag and should have ANSI 118.15 stamped on it. Laticrete 254 Platinum is one example of this.

Make sure you read the instructions on the bag. These mortars really are the best thinset of the bunch because they have to be.

Exterior tile installation over occupied space

Plywood: For going over plywood with products like Ditra or any other membrane the thinset will have to have an ANSI 118.11 rating on it. This is a requirement. This rating means that it’s been tested to bond to plywood. Don’t stick tile directly to the plywood subfloor no matter which thinset you use.

Ditra and Kerdi: For Schluter products like Ditra and Kerdi they want you to use an unmodified mortar. The exception is when you are installing Ditra on plywood (see above). This also would apply to Ditra Heat. I’ve listed specific products in the chart above. Some of these can be found at big box stores.

For large tiles, you are going to want to use an unmodified thinset that specifically says it’s ok for large tiles. The one I prefer is Bostik Ditraset. It can be used for any size tile and works great with Schluter products. I’ve never found it at a box store though.

The other one that would work is Mapei’s uncoupling membrane mortar which can be found at Lowes.

Another good option for big tiles over Schluter products is Mapei Kerabond T. Although, you’ll probably find that Mapei’s uncoupling membrane mortar, which can be found at Lowes, is more readily available. This will work too.

Update: Schluter now has its own line of thinset mortars now called Schluter Set, All-Set, and Fast-Set. The last two being modified. All are approved for their products.

Why Schluter Ditra is so cool: Uncoupling membranes explained

Porcelain Tile: Most thinset manufacturer’s want you to use a modified mortar for porcelain tile. Porcelain tile is near impervious and can be difficult for the mortars to grab a hold of which is the reason for the modified mortars. They grab better.

The exception again is Schluter products which want unmodified mortars used.

Backer board: For backer board on floors, specifically cement board and fiber cement boards (think Hardibacker), it’s my understanding that it doesn’t matter which thinset you use. The thinset doesn’t need to bond to the plywood.

Instead it’s part of a system with the fasteners. The nails or screws hold it down and the thinset holds it up. So this is an example where you don’t need the best thinset- it seems the worst will do.

But some backer board manufacturers have a more specific set of instructions. As always, follow instructions.

Tile Backer Board Breakdown

For walls, you’ll want to use a modified mortar to tape and mud the seams. Make sure you use alkaline resistant mesh tape.

Mesh Tape: Don’t Skip This Step

I recommend staying away from Denshield and other similar gypsum-based products in wet areas but if you want to use it make sure to read the instructions. You’ll need to waterproof the seams and they don’t waterproof the way that you would think.

Wall tile:  They do make a good number of lightweight thinsets now which work great for walls. They can help keep your tile from sliding down. An example is Tri-lite from Laticrete.

Hopefully this helps clarify some of the mystery around the many different thinset products. If I’ve left anything out or you have any questions please ask in the comments below. Always read the manufacturer’s instructions for the products that you will be installing.

Also see:

Part 1 Thinset Decoded: A buyers guide to purchasing the right tile adhesive

Trowel Size Matters

Reader Interactions

Comments

  1. Hi. Is there a substitute for Laticrete 6701 by Versabond or something similar? We are putting in a shower and making our own bed/pan.

    Also we used a thin set modified, not large us modified for 6×12 floor tiles. Seemed to work fine… Should we expect any problems?

    And finally what do you recommend for the shower walls with same tile? Is the Versabond modified thin set OK?

    Thanks for your time, greatly appreciated.

    Reply

    • I think you probably mean 3701? Mapei makes a really nice product called 4:1 that can be used for mud beds. Also you can use sand topping mix found in the concrete section of the hardware store. This is usually a 3:1 mix so you’ll need to add play sand to it to get out to 4:1 or 5:1

      Also Versabond is fine for 12 inch tiles.

      Reply

    • Megalite thinset from Home depot worked great, for 10″ X 14″ ceramic tile as well as the Glass mosaic accent in my shower, over cement board treated with 4 coats of Redgard .

      Reply

  2. Any experience laying 20″ porcelain tile over cutback adhesive residue on concrete slab (has been scraped down to residue by previous owner and yes there was probably asbestos so I will not be doing any other prep work)? Researching what Home Depot sells I was going to use Versabond LFT but is it the best choice out of everything out there? I don’t mind special ordering if there is a big difference. Thanks.

    Reply

  3. If you are installing predominantly large format tile (12×24) with a break of mosaic (12x12x8mm – 1×2 inch brick pieces) is it okay to use the LFT thinset on the mosaic or will I need to use two types of thinset?

    Reply

  4. I am installling Ditra in our bathroom and found your infographic which is really helpful. I am planning on putting it down with Mapei UltraFlex 2. I will be putting down 12×24 ceramic tile on top of it. I was planning on using Mapei Kerabond T to put it down, but you state above:

    “For large tiles you are going to want to use a thinset that specifically says it’s ok for large tiles. The one I prefer is Bostik Ditraset. It can be used for any size tile and works great with Schluter products. I’ve never found it at a box store though. The other one that would work is Mapei’s uncoupling membrane mortar which can be found at Lowes.”

    I can’t find the Ditraset anywhere locally, nor can I find the Mapei Uncoupling Membrane Mortar. Will I be okay with the Kerabond T?

    Reply

  5. I actually have a choice here- How would you rank these for installing ceramic tile 12×12 and 18×18 tile on top of Ditra? Kerabond T, mapei Uncoupling membran mortar, Mapei Floor Tile Mortar, Bostic Ditra or laticrete 317? I dont want to buy 2 different types of mortar due to size of the tile, but will if I have too. thanks

    Reply

    • Kerabond T is at the top of the food chain and Ditra set is a good option also. If you can get one of these two then I wouldn’t worry about the others. 317 is good for the 12’s but not so much for the 18’s.

      Reply

  6. Hello, we are doing a Lowes brand style selections mountain bend camel 48″x12″ procelian wood plank tile. My questions are
    1. Should we have our contractor Use the 4xlt medium bed thin set you mentioned on another page?

    2. Ive read most everything you state about these large format tiles other than checking every tile for chips etc and using the best thin set should we ask if they use a leveling system to prevent Lipage? They say on the box that the edge is rectified on the specs.

    3. What is the smallest grout line you recommend on this? We had tile guy tell us 3/8″ but I was after 1/8″ he said these are not a true rectifiesd edge because there is avery tiny bevel near the top…

    4. Any extra information you can provide? This is a room where my Father in law passed and I want the least issues for my Wife’s sake, so she can walk in and be happy in there again. Thank you

    Reply

    • I don’t promote any brand of thinset. Medium bed is what’s supposed to be used for plank tiles. There’s many options available in different brands that can be used.

      I don’t think a leveling system should be required. I think a flat installation is what should be required. Have the contractor explain to you what they can do and what you should expect the floor to look like. If that’s exceptable to you then all you have to do is make sure that it meet’s those expectations.

      The same goes for grout joints. If 3/8″ is too much (I don’t know anyone that would except that) then have them show you what the finished product will look like. It is possible that 1/8 inch isn’t practical with the tile that you’ve selected. If this is the case you may want to reselect.

      If you feel that the contractor isn’t capable of delivering a floor to reasonable expectations then you should move onto someone that can.

      Reply

      • Thanks for the knowledgeable and quick reply.
        I think I messed up putting 3/8″ grout line I think it was 1/8″ to 3/16″ .
        I guess the main thing is getting some one at least in the Punta Gorda FL who 1st seems confident working on this large format and 2nd that they can assess the concrete floor for level then Correct?

        Reply

  7. Hello,
    What mortar do you recommend using between plywood underlayment and hardi backer and also what type of mortar do you recommend between the hardi and porcelain tile

    Reply

    • For underneath hardiebacker you can use any mortar that you want. The cheapest is fine.

      The other depends on the tile and what you have access to. The chart above should help you figure out what you need.

      Reply

  8. Great website. You’ve already answered most of my questions. One more for ya…

    Is white thinset on slate tile backsplash ok? I know you want white for lighter stones, and I’m assuming grey is for darker (?). I ask because my local box store has white Prolite in stock, but grey is special order.

    I can’t imagine the white is going to show through dark slate stones, but maybe I’m missing something.

    Thanks again. Matt

    Reply

  9. Hello,
    Thank you for all of the information particularly on the recommended type of mortar to use given the different tiles. Iam refinishing my basement floor and using a 12×24 porcelain tile over concrete. I think am now okay on which mortar to use thanks to you info above.

    My concern now and question is this… about 7 years ago i painted the floor with a “satin latex” paint and install carpet over it. After a water heater leakage, I decided to pull the carpet and now deciding on install tile.
    After reading a number of article online, it appears that i cannot install tile directly on top of painted concrete floor because the mortar may not bond well to the concrete and tile. And that I must 1) install a type of board over the floor or 2) remove as much of the paint as possible, at least 80% or 3) use Scarifier or Concrete Grinder. A few of the article were dated close to 2 yrs ago, or older.
    – the basement is about 680sf and iam trying to do it myself. Doing any of the above will be time consuming and possibly costly.

    Iam heading to a tool rental place to see what i can rent but would like to get your opinion first.
    What’s your recommendation? Is there any mortar that i can use over paint?

    Thank you in advance,

    Reply

    • The best way is to scarify the floor. A rental store may have a walk behind grinder but it could be done with a 7 inch grinder with a turbo cup grinding wheel which you would be better off buying your own and putting it on their grinder. This would be cheaper but it would all have to be done on your hands and knees. You would want to make sure you have a large shop vac and a dust shroud for the grinder with this set up. The rental store may or may not have this.

      You don’t need any board over the concrete. You could look into a product called Greenskin which is a peel & stick product. I don’t know if they will ok it over paint or not. Also Mapei makes a product called Eco Prim Grip. It’s for going over asbestos tile and that sort of thing. You’d probably want to check their tech line before committing to this method.

      Reply

  10. I’m installing 13 x 13 ceramic tile over a vinyl tiled floor. do you recommend the Ditra membrane? And what adhesive over the vinyl?

    Reply

    • This one is complicated because it depends on a few other factors. It is OK to go over vinyl flooring but if the vinyl flooring is over particle board underlayment I wouldn’t do it. If it’s over concrete then that’s a much better situation.

      Vinyl tile flooring is a different situation. Especially if the vinyl tiles have asbestos. Probably your best bet is to go over them with a bonding primer. Custom had one called MBP, I think, and Mapei’s is called EcoPrim Grip.

      Then you can stick directly to the vinyl or use an uncoupling mat. If you do it in this manner you should be able to use a normal modified mortar that has an A118.4 stamp on it. Versabond flex, 253 gold, ultraflex 2, something along those lines.

      If you go directly over the vinyl use a really good mortar. Megaflex or 254 platinum or something along those lines.

      Reply

  11. Thanks for your prompt reply! So I can apply the ceramic directly over the vinyl tiles? I saw on other sites (before I found yours) that recommend using an uncoupling mat for such applications. I have the vinyl (it may be asbestos- they’re 12 x 12) over a 7/8″ plywood subfloor. What do you recommend?

    Reply

    • If it’s over a wood sublfoor I would highly encourage you to remove the tiles and the underlayment that they are stuck to. That’s going to be the best path forward.

      Otherwise the vinyl is going to have to pass a certain protocol. It has to meet certain requirements. Such things as being well bonded, not cushioned, etc. If it doesn’t meet the minimum requirements then an uncoupling membrane isn’t going to fix it. So you’ll need to determine if your floor can have tile installed over it the way it is right now.

      Customs Redgard uncoupling membrane is ok to go over vinyl tiles. Ditra says it’s ok to go over vinyl but doesn’t specify vinyl tiles. Here’s a link to Custom’s bonding primer. I really think that one of these bonding primers is going to be in the plan if you decided to leave the vinyl tiles installed.

      Going over vinyl isn’t a cut and dry application and you’ll really be best served to call the tech department of whichever products that you intend to use. They should spell out for you a path to success. But if you can remove the vinyl that’s going to be the best way.

      Reply

  12. I’ve noticed some comments on Kerabond T. Can this be used with installing membrane/installing smaller tile as well, or should i stick with regular Kerabond?

    Reply

  13. Is there any particular rapid set mortar you’d recommend?

    I’m tiling the walls and floors of a small (5’x8′) bathroom with 18×18 tiles on the floor and 12×12 on the walls and was hoping to use a rapid set LFT mortar to not have to wait a full day to grout.

    Reply

    • The only two that I’m familiar with are Laticrete’s 4xlt rapid and Custom’s Megalite comes in a rapid formula as well.

      I’m sure there are others but those are the two that I know of of the top of my head.

      Reply

  14. i just made a shower pan using the sandtopping+ sand.
    i did not use play sand as i see u mentioned here.
    i used the sand home depot sells.
    is this going to be a problem?
    thanks

    Reply

    • It won’t necessarily be a problem but you might want to make sure that the surface isn’t slicked like concrete. 3:1 will make it tougher for water to flow through so you want to make sure that you’re not impeding that in other ways.

      But having it 4 or 5:1 is preferrable.

      Reply

      • i read (on john bridge site i think) that up to 30% sand was best, so thats about how i mixed it.
        it dried hard but there were a few small areas of loose “grit” which i removed and filled with a “sloppy” thinset (this was suggested to me elsewhere)
        how does that all sound now?
        supposed to start tile tmrw

        Reply

  15. i have a 3/4″ gap around the shower pan once the tile is set. rather than have a 1/2″ line of tile on that outter edge, can i just bring the wall tile to the floor and but the floor tile against it?
    thanks for ur advice

    Reply

    • What I like to do in these cases is put in the 3/4 inch cut when you do the shower floor. Then install the wall tile on top of it. It makes for a little more time on the shower pan but the wall tile will go easier. It’s easier to shim off of the bottom when the tile sits on the shower pan tile.

      Also if your walls aren’t perfectly straight you won’t have too big of a gap in some places.

      Reply

  16. I’m installing a marble mosaic. The sheet is 12×12 but each tile that makes up the mosaic is quite small. Should I use a modified thinset such as Versabond flex or CMB Marble, Granite and Travertine?

    Reply

    • There’s nothing wrong with installing marble with a modified thinset. In fact, it’s what I would recommend although if you are installing over Kerdi then they would like you to use an unmodified. Probably the Versabond flex would be the way to go with the mosaic unless you would need to build up the mosaic sheet significantly. Which would be unadvisable and make a huge mess.

      Reply

      • Thanks for the response. I’m installing the mosaic over cement backerboard. Do you think a 1/4″ v-notch trowel would be good?

        Reply

  17. Hello,

    I want to create a mosaic tile piece(s) across a 19 feet by 6 feet freestanding vertical painted plywood wall in a living room. Can I seal the wood with a sealer and then stick the tile pieces directly onto the sealed wood with a modified thinset mortar? I mean I will not have issues with moisture or foot traffic because it is a wall. However, if this is not recommended would you recommend Kerdi, Ditra, Easymat, or maybe even Tavy Thin Skin System? I do not want to put a backboard because it is a free standing wall and I do not want anymore weight on the wall then it has to bear with the mortar and tile pieces. Thank you

    Reply

    • It depends on the plywood. If it’s the really nice 1/2 inch AC exterior plywood then you’re in good shape and don’t need to do anything to it. If it’s something else- maybe thinner or flimsier then you’ll need some sort of membrane over it.

      A sealer probably isn’t what you want. I think it would prevent mortar from being able to grab into the plywood.

      For a membrane, you don’t need it to be waterproof. You just need it to work. So I would lean towards a peel & stick type membrane like maybe the Tavy Thin Skin or Easymat.

      You could also try a foam board like Wedi or Kerdi Board. They come in thinner sizes (1/8 inch) and can be glued with a urethane glue or screwed on. This would be a nice option because they are light weight and would probably add a bit of rigidity to the wall.

      You may even be able to use the thicker foam board panels instead of plywood depending on where you are at with this process.

      Hopefully, that’s helpful. 🙂

      Reply

  18. Hi. I just bought 6″ x 24″ tiles and was told to buy Mapei Ultraflex 1 but it doesn’t say for large tiles anywhere. Should I return these? Also is the 1/4 by 1/4 the right trowel to use?

    Reply

    • Ultraflex 1 isn’t what you want. Mapei has a mortar called Ultraflex LFT and another called Ultraflex LHT. Either one of those is a good choice. The LFT is the better of the two but the LHT should be adequate. LFT stands for Large Format Tile. LHT stands for Large and Heavy Tile.

      You’re going to want to use a 1/4 x 1/2 inch trowel or even a 1/2 x 1/2 to install the plank tiles.

      Reply

  19. Hello! Thanks for the website this information is great! I am installing 6×36 wood plank looking porcelain tile on the floor in my bathroom. I have a wood subfloor and I screwed down 1/4″ wonderboard. Was I supposed to put thinset under it? I was planning on using versabond LFT. On the wonderboard and that is it.

    For the tub surround I have 12×24 tile and was planning on 40 mil pvs stapled to the studs the 3/8 hardibacker screwed to the studs then redguard on top. For the thinset whatbwouod you recommend? Home Depot said Prolite or Flexbond. But neither say LFT on them. Or should I just use versabond LFT on the walls on top of redguard?

    Thanks! Jake

    Reply

    • You can use either Prolite or Versabond LFT for those tiles. Prolite is an LFT mortar even though it may not say so on the label.

      Also, you should definitely thinset under the Hardibacker. I’ve seen too many cracked and loose floors as a result of people skipping this step. You don’t have to use the LFT under the backerboard. Any bagged thinset will work for that.

      Reply

  20. Hello!
    Using Ditra over concrete.Tile will be 18″x18″. What is the best application and brand of thinset for both 1) applying the ditra to the concrete and 2) laying XL tile to ditra?

    Thanks in advance,
    Matt

    Reply

    • I don’t prefer one brand over another but the bottom boxes in the infographic contain particular product recommendations. You can also purchase Schluter Allset which is Schluter new in house mortar that the recommend for all of their products.

      Reply

  21. Please help! What LTF should be used on newly poured concrete (already cured)? House is on corner with about 1500 feet of covered porches and walkways to street. Material to be applied is 16″x 24″ slate with a thermal finish on top. There are so many products that I’m confused between Versabond, ProLite, TEC, etc. I do not need rapid curing.

    Reply

    • What makes the difference is whether the application is outdoors, or not. If it’s indoors then you can use most LFT mortars that you’ll be able to find. If it’s outdoors, which it sounds like it is, then your options are much more limited. Something like MegaLite would be best. Other brands probably have a product that would compete with Megalite and those would probably be OK also.

      Not sure if you’re saying that the slate has a thermal finish or if the concrete does. You don’t want any coatings on the concrete if the plan is to tile.

      Reply

  22. Great chart. However I’m confused by the must say ansi 118.11 but them it points to ansi 118.4. I’m installing ultra over plywood and then 12×24 tile on top. I can get the mapei uncoupling mortar but did find it very sandy when using it on Kerdi band (Maybe a separate issue). Anyway, from the chart I’m thinking I need mapei porcelain to bond the ditra to the plywood and mapei uncoupling to bond tile to ditra. Is that right? Would you also use mapei uncoupling to bond the same tiles to a Kerdi panel wall?

    Reply

    • ANSI 118.11 is the standard for going over plywood. If it doesn’t say 118.11 then you don’t want to use it on ply. It probably will have both 118.11 AND 118.4 listed on it.

      So you’ll want the 118.11 to bond the uncoupling membrane to plywood. Then the uncoupling mortar to bond the tile to Ditra. And you can bond tile to Kerdi with it also.

      Reply

  23. I am installing LFT 6” x 36” wood grain tile over a concrete floor. It has been recommended that I install some kind of uncoupling membrain like a paint on type or the ditra. There several thoughts about this and is it that serious. I have installed tile over concrete for years and have not heard of uncoupling products before. We all know there is some crack issues with concrete but isn’t that what modified thin set is for? I want to do what is best but spending an extra $3,000. for uncoupling products like ditra is a lot of extra cost to an already expensive tile. Is there anything less expensive that will give you the same benefit? Or is using a good modified thin set sufficient? Can you lead me in the right direction? This is a new house that I built myself and I don’t want to short cut myself at the end.

    Reply

    • Good question. They say there are two kinds of concrete: concrete with cracks and concrete that hasn’t cracked yet.

      First of all, thinset does nothing for crack prevention. It’s an adhesive and should be used for this purpose- not to prevent cracks. I will mention, that there are a few exceptions, for instance, Laticrete has a product called Sound and Crack Adhesive (Now called 125 Tri Max).

      Another thing that you may find surprising is that Ditra is another product that isn’t a crack isolation membrane. Although they do advertise it’s movement capabilities, and it may help to prevent cracking to a limited degree, it’s not an A118.12 crack isolation membrane.

      So if you want to use an A118.12 CIS membrane then I would look for those types of products. They tend to be sheet membranes and not waffle-type membranes. The one I prefer is Noble CIS but there are others on the market.

      If the concrete doesn’t have cracks in it then you don’t necessarily need a membrane. However a membrane does provide some insurance towards future cracking and does give the ability to allow the tile to move independently of the concrete as the two surfaces do move move at different rates. But a lot of tile gets installed over bare concrete and most of it is ok.

      An inexpensive CIS memebrane is a liquid waterproofing membrane such as Redgard or Hydroban and that might be a happy medium. Read the instuctions, use reinforcement fabric, if necessary, and get the proper thickness.

      I recommend also reading my post on movement joints as that will help immensely also.

      Reply

  24. Mixing mortar types. So, apparently the premixed stuff is the work of the devil based on the reaction I got from everyone I asked about it. But that is after I used premixed mortar (Simple Set Pre Mixed Thin-Set Mortar ANSI 136.1 Type 1 – non modified, I believe) when taping the seams/screw holes over the HardieBacker cement board. For tile mortar we unsuccessfully tried Superior Adhesvive and Chemicals Pro Bond Non Sag Thinset Mortar. This is a polymer modified thinset. We were having trouble with the bottom tile row and stopped. Removed bottom tile row and most of the mortar. Some of the tile did not want to stick. I believe this had more to do with our technique and the thick tile we selected 1/4″ or so, 1 1/2″ x 3″ subway tile, than the mortar type. But now I have two different types of mortars on the backer board, one pre mixed, unmodified (used to tape seams and screws holes) ,the other modified (started to use on for tiles, but was removed. Just a residual layer on the bottom row shows). Will this be a problem? What are my choices going forward? Thanks, D

    Reply

    • No. Those aren’t a problem and it was a good choice to move on from the premixed SimpleSet.

      I’m surprised that the other mortar didn’t work, though. Although I don’t know anything about that brand it sounds like the kind of mortar that would work well for what it is that you are doing.

      If the problem that you had was that the tile was sliding down then you might try to mix it a little thicker.

      If the problem was that the thinset was coming through the joints then you might try a smaller trowel.

      1/4″ x 1/4″ square notch would be what I would try first but you may have to go with a 1/4″ v-notch instead.

      Reply

      • We were using a 1/4″X 1/4″ square trowel. The problem was with the wet saw, cutting tiles. I did not know to dry off the tiles before putting them on the wall. The wet tiles was messing up the consistency of the mortar.

        Thankful for the quick reply.

        Reply

  25. Kitchen backsplash substrate. After scraping a bunch of old stuff off of the wall I have a mix of old oil-based paint (probably has lead in it – I plan on testing), old plaster (original to 1948 house – brown layer with white layer on top), new plaster patches (from kitchen reno in 2014) and a small area of newer latex paint. Everything that is remaining seems pretty solid. I also plan on using Durabond 90 and Fibafuse tape to fix a couple of drywall patches. I was thinking of using a de-glosser on the paints, then priming everything with CBP MBP primer. My biggest question is – is priming really necessary given all of the different things going on? Does thinset stick to EVERYTHING, or will the plaster and Durabond dry out the thinset and make it fail? I have researched this and cannot find a consistent answer. My tiles are 3×6 ceramic and I plan on using Versabond or Versabond Flex with a 1/4 x 1/4 trowel. I am also considering using a non-sag thinset because I am a bit of a newbie at this.

    Reply

    • You need some sort of primer over any areas where bare drywall compound if exposed. The primer can simply be paint primer it doesn’t need to be a multi surface primer.

      But there’s nothing wrong with overkill either. Make sure to clean the painted areas so there’s no oil or grease left on them and you should be ok.

      Lightweight non-sag mortars are nice but if you are stacking the subway tile on top of each other then it may not be necessary.

      Reply

  26. Doing 6″x36″ on the floor and 12″x12″ (11.5×11.5 real size) on the walls. CBP materials are readily available here (HD) so I’m looking at their thinsets. The bathroom is pretty small so I’d rather pay a bit more for the better material. Sounds like I’ll need CBP Natural Stone and Large Tile (used to be called Marble, Granite & Travertine) for the floor. Was considering CBP FlexBond for the walls but could use Natural Stone and Large Tile mortar for the walls as well: a choice between crack protection and sag resistance.

    Do you have any opinions on CBP FlexBond? Would it have much benefit for walls in a small bathroom? Is the sag resistance worth it for 12×12 porcelain tile? I understand that the large tile mortar is actually medium-set. Is it less effective when used in thin-set applications (in a thinner layer)?

    Thank you

    Reply

    • I don’t know that Flexbond is advertised as being a non-sag mortar. Maybe it is. But I think if HD has Prolite (my local HD carries it) that would be the mortar to get for both walls and floor. It’s an LFT that, because it’s lightweight, will help with keeping tiles from sagging. Note: results may vary.

      Flexbond is fine on the walls but the Large Tile mortar is what you would want for the floor. Nothing wrong with using it on walls though.

      Reply

      • Sorry, poor wording on my part. Flexbond isn’t billed as non-sag. I was trying to ask if it’s worth using non-sag (CBP NS&LT or Prolite) for 12×12 wall tile or if flexbond’s crack resistance is more beneficial.

        Reply

  27. Hello I am planning on installing tile over sheet vinyl flooring. The vinyl is in good shape but is all glued to plywood. It is glued to 1/4 inch plywood which is nailed to 3/4 inch subfloor. Is it possible to install tile over this type flooring without removing the vinyl flooring. Thanks

    Reply

  28. Do you have any opinions on drywall joint compound for use in a bathroom? Do you use anything special to join backer board to drywall or do you use something mold/moisture resistant? I was hoping to use mold resistant compound on all the drywall in the bathroom but it seems hard to find. Especially concerned about the ceiling above the tub surround.

    Reply

    • I think drywall guys just use normal compound that gets mixed together with water. USG Silver it’s one of the products that I’ve seen used. It’s probably best to get other opinions on that.

      But if you are taping from drywall to backer board I would use thinset as that joint will be covered with tile- usually anyways.

      Although if you’re talking about ceiling drywall to backer board walls then you probably would want to do that inside corner with wall compound.

      Reply

      • If I use joint compound in the corner between CBU wall and drywall ceiling but I use thinset on the vertical corner between two CBU walls, then how do I handle the 3-way corner between the 2 walls and the ceiling where the two types of joint finish meet? Should I finish the vertical CBU corner with thinset, let that dry, then go across that with the drywall tape (fibafuse) and joint compound? The drywall tape isn’t alkaline resistant, will it deteriorate just from being on top of the thinset?

        Reply

        • I think what I would do is run the alkaline resistant tape vertically up the cbu to cbu corner. The leave the thinset (used for the corner tape) shy of the ceiling by maybe 1-2 inches. Then tape the ceiling with the drywall tape and include the very top of the vertical joint when you apply the drywall compound.

          The tile will cover the cbu tape up to the ceiling. But I think you definitely want to use the drywall tape at that top cbu to drywall joint.

          That’s just my opinion. There might be a better way.

          Reply

          • Sorry to revive an old post but I wanted to get everything straight as far as what types of joints get what.

            I have 3 types of surfaces: gypsum ceiling, gypsum wall, and CBU wall. Gypsum-to-gypsum, wall or ceiling, gets drywall compound. CBU-to-CBU gets thinset. CBU wall to gypsum wall seam gets thinset (same as CBU-to-CBU) where it’s covered by the bullnose border tile. These joints will be 2-3″ from the edge of the tile and will be covered by redgard. There will be one CBU-to-gypsum wall joint at an outside corner which gets a corner bead and joint compound because half the joint is not covered by tile and it is in a relatively dry area. Does this sound right?

            The last case is what I was asking about above: the CBU wall to gypsum ceiling joint. If I finish it, it has to be filled with joint compound because half of it is exposed. The ceiling is painted and the wall is covered with tile all the way to the top. If I was to treat this case as a regular drywall wall to ceiling joint, the wall board butts up against the ceiling board and helps support it. Does it make more sense to treat this more like an upside-down wallboard to tub joint? By this I mean leave a small gap between wall and ceiling, apply redgard up to the top, fill the gap with silicone, tile to the top, and caulk the wall-ceiling corner.

          • Yes, that’s fine. What you’ll need to watch out for is the silicone on the ceiling since that gets painted and paint won’t stick to silicone.

            So you might try: silicone at the wallboard/ceiling joint–>tile–>paint the ceiling–>then carefully caulk with silicone the tile/ceiling joint.

            (Tile and paint can be switched in the above scenario)

            Even doing this can cause some issues with silicone and new paint. When you clean the silicone it damages the paint them it’s difficult to touch up because it’s silicone.

            But there’s no way you’ll get a clean line if it’s silicone before paint.

          • Wouldn’t that paint/silicone interface be an issue regardless of how I finished that joint? If the tile goes up to the ceiling, the wall/ceiling corner gets silicone because it’s a change of plane. Or would you normally go with grout there?

            I was thinking redgard on CBU then primer on ceiling (vapor barrier primer) then caulk the gap then tile then grout then paint ceiling then caulk the corner. First caulking is probably clear or white silicone, fills the gap, and supports the ceiling. Adheres to the redgard coat on the CBU at the bottom and the edge of the primer coat at the top. Second caulking is cosmetic, uses color-matched caulk, and adheres to tile at the bottom and edge of the ceiling paint at the top. I’ll mask with painters tape before I apply it so it doesn’t go too far out. When I have to redo it, taking the old caulk out will probably remove some paint which will have to be touched up before the new caulk is applied. Sound like a good plan?

            If you’re wondering, I’m an engineer, I do test planning, and I bring my work home with me. And, yes, I am crazy. 🙂 Thank you for you help.

          • Again I think I need to work on my reading comprehension and I wish I could edit my posts. I think we’re on the same page with order of paint/tail/caulk procedure and that long paragraph is just wasting your time but now I’m wondering if people avoid tiling all the way to a painted ceiling because of the silicone/paint issue.

          • Your plan is sound and my comments were probably getting too far ahead anyway.

            Most every bathroom I do goes to the ceiling. It seems the only exceptions in recent memory have been homes that were trying to keep in the period and style of an older home.

            I think most people don’t caulk where they are supposed to and aren’t even aware that silicone and paint don’t mix.

          • One case I’m still not sure about: the vertical seam between CBU and drywall where the tile ends at the edge of the tub. There is a radiator enclosure right next to the tub and I only have 4-3/4″ to work with. I can’t really space the vertical 2-3/4″ bullnose row away from the tub with regular tile without it looking strange. So tentative plan is CBU directly above the tub and gypsum directly adjacent to it along the wall, finish that joint with mesh+thinset, and redgard over the joint and gypsum as far as the bullnose reaches.

            This makes me uneasy since I’ll be putting redgard and tiling over gypsum and that corner on the outside of the tub is gypsum, not CBU. That seems like a problematic area because of water that drips over the edge. Is the right way to go? At least it is only this way for the side of the tub opposite the shower: the plumbing side has wainscot so it’ll be CBU up to 4 feet above the floor.

          • If that’s the best solution then that will work. I would make sure that there is a gap between the drywall and the tub that can be filled with silicone. Otherwise, it’s a sounds plan.

  29. I am using 1/2″ USG ultralight foam backer board for shower walls and will be installing 12×24 in. porceleain tiles. I called USG today to find out what type of thinset to use and he showed me on their website where instructions issued 2017 state to use thinset that meets 118.1 (unmodified) or 118.4 (modified). After I arrived home from work today, I noticed that instruction sheet is no longer on their web-site. It doesn’t seem logical that either type of thinset is suitable for their backer board…one has to be the best type of thinset. The instructions on their website for the board from 2015 state to use unmodified thinset for installling the USG 5″ band over the seams, but no mention of what type of thinset for the tiles…so which is best type of thinset in this situation for foam board with large format tiles? I could not tell from your flow chart.

    Reply

    • I took a look at the information and there are two different sheets: the installation instructions and the technical data sheet (submittal sheet). The data sheet has a 2017 date and under “standards” lists 4 different mortar types. Personally, I wouldn’t use a A118.1 and would use a minimum 118.4 for the bonding of the sheet and an LFT for installing the tile.

      Reply

  30. If I’m putting up 12″x12″ wall tile over RedGard on cement board, is there any reason why I shouldn’t use a cheaper thinset to finish the cement board seams and then use something nice like prolite to actually put up the tile? I thought I’d get some more affordable latex-modified thinset to do that and attach Ditra to the floor. Are there any mortars that are too crappy to finish cement board seams with?

    Reply

    • That’s fine. I don’t know if there are mortars that are not recommended for cement board seams. But for Ditra you’ll want to use an A118.11 mortar. If it has that stamp on it then it’s OK for installing over plywood. This is assuming that you are installing over a plywood subfloor. If it’s concrete then you could use an unmodified, if you want.

      Reply

  31. i am installing a slate tile over concrete backer board around my fire place. The largest tiles are approximately 6×8 inches. The area gets pretty hot after the gas logs are on for some time. What is the best product to apply to the tiles with in an area with extreme temperatures and what kind of grout to use?

    Reply

    • I think it depends on how hot you’re talking about. Slate and other tiles are installed around fireplaces all the time and a lot of them aren’t installed with premium mortars.

      If you think that your fireplace will get hotter than normal then it’s probably best to call the tech line of one of the manufacturers to see if they will spec a particular kind of mortar.

      I like the high-performance type of cement grouts for this type of application. Epoxy would probably be fine in higher than normal heat also and I don’t see anything on the data sheets that say that it shouldn’t be used for this type of application.

      Reply

  32. You really should update the leading text information on your web page to correct the current Schluter recommendations for unmodified vs modified thinset.

    Reply

  33. Hi. Installing 12″ marble tile on floor, counter, and shower walls over GoBoard. Any recommendations on the thinset to use?

    Reply

  34. I bought a durock shower system. When I got it all it talked about was unmodified thinset. After I installed it. I went back on the website and now they they are saying that you can use just about any thinset. I want to install cream marble on top of the system. Should I stay with the unmodified thinset or should I use another??

    Reply

    • I very much like modified over non-modified for most things but specifically for sticking to porcelain tile.

      Since you’re installing marble I don’t see an issue with using a quality white unmodified mortar.

      Reply

  35. As a general question, if you have a row of bullnose tiles over the CBU-to-gypsum transition, where do you have the seam between CBU and gypsum relative to the bullnose edge and do you finish it with thinset or drywall compound? If the thinset is used to finish the seam and gets feathered out over the gypsum beyond where tile covers it, does it become a problem or would you just avoid feathering it out that far?

    Reply

    • Don’t let thinset get past the end of the tile. Tape it off if you need to.

      It’s only going to cause problems for the drywall finishing if it’s outside.

      Reply

      • How close to the outer edge of bullnose tile do you feel comfortable placing the seam?

        Also at this point, I’ve asked you for enough help that I think I should give something in return. If you tell me where you eat lunch, I’ll call them up and cover a meal. 🙂

        Reply

        • Ideally, I guess you would want it 2-3 inches in from the edge but you also want the seam outside of the shower.

          So the bottom line is that it just needs to cover. I did one just recently that the tile only covered by about 0.5 inches.
          I still got mesh tape on there and cut the excess tape off that stuck out past the tile but the wall didn’t have to be repaired.

          Reply

        • Also, you don’t owe me anything. The questions that you’re asking are helpful to other people and every blog needs active community members.

          Thanks for participating and I’m glad that you are getting value of my blog. ?

          Reply

  36. Great site – very helpful information – thank you!
    I am putting glass tile on a concrete wall (interior, but it will be humid). Should I use glass tile adhesive, or would prolite work for glass on a wall?
    Thank you!

    Reply

    • See if the glass tile manufacturer has a recommendation first. Otherwise, I think either mortar will work. I might lean towards the glass specific aggressive if it were me.

      Reply

  37. I’m putting some woodgrain tile on a wall. I know, technically it’s “large”, but barely — the tiles are only 3″ X 15.75″. Would you still use the large tile thinset? Or can I use Mapei Porcelain Tile Mortar? Thank you for the time you spend helping us poor DIYers!

    Reply

  38. Great chart! Note that if you’re installing Durock membrane or band USG wants you to use unmodified thinset just like Kerdi. I don’t know about other membranes…

    Reply

  39. Whoops! As Ronaldo noted above USG have changed their tune and now allow almost any type of thinset (“A118.1, A118.4, A118.11 or A118.15”). Never mind…

    Reply

  40. Hello. First of all, thank you for posting this article/website. Secondly, I have a question for a project I’m trying to have done soon. Which of mortar(s) do you recommend I use to cover 700 Sq. Ft. with Travertine Stone Tile (18×18)? It’s for an indoor residential job.

    Reply

  41. Hi-
    I am installing 8×18 stacked travertine sections as backsplash. After reading your site and many comments, it seems I should use a white large tile mortar. My question is, should it be unmodified or modified because of the travertine?
    Also, should I use a 1/2″ x 1/2″ trowel since the travertine is so thick?
    Lastly- since the actual pieces are so small, what do you think about using a dremmel wheel to cut them instead of a tile saw?
    Thank you!

    Reply

    • Correct on the mortar: white and LFT. I prefer modified but either would be OK. 1/2 inch trowel is good.

      A dremel might work ok. Travertine is soft and it’s worth a try if that’s what you have.

      Reply

  42. Hello, Thanks for the informative article. 3 different questions: #1 wanted to verify that “large format” mortar is also acceptable to use with mosaic tile (shower floor). #2 we have a bathroom remodel to do that we want to do the walls floor to ceiling with tile. One of the walls has a pocket door. Plan was to remove the sheetrock and install 1/2″ cement board, then tile. Any special advise concerning the wall with the pocket door? #3 Lastly – I’m reading conflicting information regarding cement board under floor tile – one says just screw down (i.e. if ever want to change floor can get up easier?) other says always use thinset and fasten? Preferred fastener – screw or nail (have to be galvanized?)?
    Thanks.

    Reply

    • Most large format mortars are ok for mosaic tiles. Typically, it will say “up to 1/2 inch” or some sort of language of that sort.

      For the pocket door you’ll probably want to add additional supports on that wall, especially on the cement board seams. I know some builders will install plywood on that wall to stiffen things up. Be careful of screw length on that wall- you don’t want screws to penetrate into the path of the sliding door.

      Cement board should be thinset and fastened- it’s on the instructions of the board. Either screws or nails are fine. My personal preference is for galvanized roofing nails on floors but cement board screws are perfectly ok.

      Reply

        • I don’t think you’ll find 1/4 inch exterior ply and if you do it won’t be stiff enough. You might try 1/2 inch exterior plywood and use a product like Kerdi over the face of it to waterproof?

          Reply

          • ok, that’s an idea. I appreciate your advice. Could I ask another? We will be putting floor tile in kitchen and dining room. The floor system is wood (2×10 joist, max span 8ft). The original floor was 1/2 plywood with 3/4 pressboard on top. We will be replacing the pressboard with either T&G ply or EdgeGold OSB. I have read mixed opinions on if with that much ply subfloor and additional 1/4 of cement board is necessary, or just use a flexible grout and put the tile right on top of the ply subfloor. What’s your opinion? Thanks.

          • Technically you can install over tile over a second layer of plywood underlayment over proper T&G subfloor. It’s not something that I think is a good idea. Additionally, if the second layer of underlayment is OSB then it has to be covered.

            I would definitely use 1/4 inch cement board or fiber cement board or if height is a concern, a thinner uncoupling membrane such as Ditra or Redgard uncoupling membrane.

          • Bathroom has been gutted. Will use 1/2 ext. ply over the pocket door with membrane or 1/4 cement board over ply. Rest of walls will be 1/2″ cement screwed to studs. (Correct if wrong)

            #1 – Do I put plastic between the cement board and studs – as a vapor barrier?
            #2 – Which go on first? Wall or floor tiles (walls will be tile floor to ceiling)

            Thanks

  43. I am moving along on my tile project, thanks to your answers to previous questions.

    My shower stall has two sides each with 1/2″ USG ultralight backer board installed. Each wall will have 2 rows of 1/2″ thick, 12″ x 12″onyx mosaic tile in center with 1/2″ porcelain on each side of the mosaic tiles. The mosaic tiles have 1″ x 1″ pieces within each tile and each has a mesh backing and rows can be flexed open in either direction.

    I plan on using Laticrete 254 Platinum thinset because the onyx is porous and because water can get between the rows of the tiles since there is no room to put grout. The 254 thinset is made for use in swimming pools so I’m not concerned with water getting through the tile and because the backer board is waterproof. But to be precautious, I will put a sealer over the mosaic tiles.

    I put a piece of the mosaic on the ultralight using 254 thinset and soaked in water to test, and there were no problems with it separating.

    Each side of the porcelain where the mosaic butts against the porcelain will have a bead of the 254 thinset so doesn’t affect the mortar used for the porcelain (Laticrete XLT large format tile).

    I have the first row of porcelain installed and now I’m ready to install the first row of mosaic tile. I plan applying the thinset with a trowel with 1/16″ teeth and then spreading flat with other side of trowel to help prevent the thinset from oozing through the rows.

    I have 8 of the mosaic tiles to install for each row. My concerns are:
    1) If I install a few pieces of the mosaic and wait until next day to install additional tiles, the individual tiles may spread apart if some thinset oozes through the rows, which will result in problems with subsequent rows fitting together. This is because each tile has “teeth” that interlock with each other.

    2) If I mix enough thinset to do all 8 tiles the row at once to prevent #1 above from happening, the thinset may dry before I can lay all of them as the 254 dries very fast.

    Suggestions?

    Reply

    • Hopefully, I’m not too late on this. The mosaics are going to want to sit “below” the height of the larger porcelain tiles. What I would do is install all the wall tile first and do the mosaic tile last. You’ll probably need to use a method similar to the one I talked about in this post:

      https://www.diytileguy.com/tile-accent-strip/

      You’ll have to rig up some sort of “trowel” that will spread the thinset to the proper depth. A big, wide putty knife or maybe a piece of plywood.

      Finally, after all of that, I feel I should caution you about onyx tile in a wet area. Onxy is very sensitive and is no stranger to problems whether that be from moisture darkening or scratching. Although I can’t fault your taste, I would highly encourage a different choice for the accent.

      Reply

      • I haven’t started laying the mosaics yet.

        I will be using a 1/8″ thick orange schluter underlayment behind the mosaics but after putting the thinset between it and the backer board, the mosaics will be about flush with the porcelain tile.

        In order to help keep the schluter affixed to the backer, I’ll drill in some screws. I’m considering cutting a sheet of plywood 12″ wide x 8′ tall and screwing over the schulter in order to keep it flat/smooth until thinset dries- good idea?

        I started the porcelain tile up the wall to the right of the shower pan with 1st row of 12 x 24 tile installed, and I’m working to the left towards the corner of the shower stall. Beside the 1st row of porcelain, I will be installing the row of mosaics and after that I will install the last row of porcelain to the corner. Then I will finish the adjacent wall the same way but working from the corner to the other side.

        I decided not to install the 2nd row of porcelain in the corner then installing the mosaic between it and the 1st row of porcelain in order to avoid any chance that the mosaic may not fit perfectly between the two rows of porcelain. The way I plan on doing it, I know the mosaics will be installed perfectly between the porcelain.

        In order to install the left side of the rows of mosaic so they will be flush with the 2nd row of porcelain, I will screw in a strip of wood (with a piece of the schluter taped behind it) so it’s the same width as the porcelain and remove it after mosaics are installed.

        Regarding the mosaics, shouldn’t the sealer (511 impregnator) keep them from discoloring and help prevent scratches?

        Reply

        • I think I understand but I’m not 100% sure but the plywood trick should work and it seems like a decent way of getting there.

          Sealing stone is a good idea but it’s not a miracle product. I usually tell people to think of sealer like Scotchguard. I think that’s a reasonable way of setting expectations.

          Reply

  44. I would like to send you pics of the project and a pic of the onyx to help you better understand the comments/questions in my previous post – what email address can I send them to?

    Reply

    • Looks like this post got caught in the spam filter. To be honest, that onyx is worse than what I was expecting. I don’t think there’s a way to grout it, is there? You can install it in your shower if you want but I don’t see a way to keep moisture from getting behind it.

      It wouldn’t be something that I would recommend and I would check with the seller and/or manufacturer to see how they feel about that product being installed in a wet area. I hate to be negative on it but I just think there’s a good chance that it won’t age well.

      Reply

      • There is not enough space between the rows to grout from outside of tile One possibility is to grout by spreading open each row and put in mapei flexcolor grout and squeeze rows together then wipe off excess on face of tile – would that work?

        If it would not work and water gets behind the tile, what problems would it cause? I am asking because:
        1) I’m using USG ultralight foam board which is waterproof.
        2) The thinset I will be using is laticrete 254 platinum and is waterproof because it’s used for mosaic tile in swimming pools.
        3) In order to install the mosaic flush with the porcelain, I will be installing 12″ wide row of 1/8″ wide Schluter ditra between the tile and the foam board using the 254 thinset- the ditra is waterproof.

        Shouldn’t any water that gets between the mosaic rows flow down between them to the bottom ledge of the shower pan?

        Reply

        • So I should have clarified that water getting behind the mosaic doesn’t meant that water will get behind the wall. If everything is done with USG Durock foam board and sealed properly then water won’t get behind that layer.

          Water will get behind the mosaic piece though. Because of the shape, design, and type of material that the mosaic piece is. Water getting behind the mosaic will darken it unevenly, make it difficult to clean, and could mold behind it where you can’t clean it.

          One thing about onyx is that you have to be very fussy with what you choose to clean it with as it’s very vulnerable to etching and staining.

          So I’m not saying that you can’t do what you want to do but I just want you to be aware of the consequences.

          Reply

          • One possible way I thought of to keep water from getting between the rows is to spread open each row and put in mapei flexcolor grout and squeeze rows together then wipe off excess on face of tile – would that work?

          • It’s hard to say but I think it would be difficult to completely waterproof. Especially with the material itself bring porous. But if you do a good job I think it would definitely help.

        • If I’m not able to get the grout between the rows successfully after opening them up, I plan on putting a test piece of the mosaic on USB foam board using the 254 laticrete then applying a sealer and soak in a bucket. Approx. how long should I wait to see if any problems with discoloration?

          Reply

          • In my previous post I meant to say from last sentence: Approx. how long should I wait to see if any problems with discoloration or mold?

          • Oh. That’s tough to guess. You might try it for a week and see what happens. But it would be hard to give a timeframe problems to develop.

            Worst case would be that you replace the accent down the road if you really are unhappy with it?

          • It’s hard to say because I’ve tried to replicate staining myself and haven’t always been successful.

            I think some of it has to do with warm water and repeatedly drying out. I also think shampoo and grooming products play a part.

            But I think if you do what you are talking about I would say maybe soak it for a day then dry it out and repeat a few times. Maybe over the course of a week?

            Testing is a good idea though and I’d be interested in hearing about the results.

  47. what is the best thinset for shower wall using 12×12 porcelain tile on durock backer board treated with redguard. Thanks

    Reply

  48. I haven’t done the testing yet on the mosaic, but if goes ok, I thought of 2 options for installing the Ditra:

    1) Drill small holes in each square so if water gets in, there will be way for water to drain out at bottom (there will be 1/8 gap between last tile and ledge at bottom).

    2) Install the Ditra backwards since the white mesh is porous and if water gets to that area can drain to bottom.

    Which of two options is best?

    I was at tile store today and there is a new underlayment by Mapei called Mapeguard that’s same thickness as the Ditra. Have you heard of it and do you think it would be better to use than the Ditra behind the mosaic tiles?

    Reply

    • I’ve heard of Mapeguard but don’t have any experience with it. But I would assume it’s a quality product.

      I understand what you are saying about the direction of Ditra. If you want to reverse it you would have to completely prefill the waffles. That’s why they want that side up because it can be filled more easily.

      I can see how the waffles would trap water and the smooth side it being an advantage. I suppose you could Kerdi over the waffles also.

      Reply

  49. I applied Mapei Flexcolor CQ (a premixed grout) between the edges of a test piece of the mosaic /squeezed together and wiped of the excess. I let dry for 24 hours and worked perfect. Will be a lot of work doing that but will be worth it. Thanks for your advice

    Reply

      • I tried using the Mapei Flexcolor CQ grout on a full sq/ft of the onyx mosaic and turns out will be much more work than I expected trying to get the excess grout removed. Therefore, I decided to abandon using the mosaic tile and instead use solid 12 x 12 honey onyx. For every odd row, I plan to cut in half the 12 x 12 onyx and install a 12″ black pencil tile in middle. For every even row, I plan to cut in thirds the 12 x 12 onyx and install a 12″ black pencil tile between. I will use 1/16″ spacers between the onyx and the pencil tile for space for the grout. Questions:

        1) The original mosaic I was going to use had approx 1/4″ wide, 12″ long black wavy marble tile between each row of honey onyx, and each piece of the marble is about 1″ long and there is little, if any, room for grout between each piece. If I cut the black marble from the mosaic tiles, would there be any issues with using this as the pencil tile between the solid sheets of onyx since grout would be between the sides of the onyx and the sides of the black marble? If any water penetrated between the black marble pieces it would not go past the 254 platinum thinset behind it. As I said before, the 254 platinum is waterproof. My thinking is that water would not leech to the onyx on the sides since there would be grout between them and any water between the black marble would evaporate before mold could form. Is my thinking correct? I would like to use this wavy shaped black marble because it looks nicer than flat pencil tile I could buy.

        2) If I put a bead of clear silicone between joints of black wavy marble tile, would that prevent water from penetrating between the pieces? I’ve read that DSR-5 is good to remove silicone residue. Is that the best or is there better product to use? If you do not recommend silicone to fill the gaps, any suggestions what to use?

        3) I plan on using charcoal Mapei Flexcolor CQ grout between the porcelain tiles on each side of the onyx that will be installed in the center. I was considering using a Mapei flex color grout about the same color as the honey onyx between the onyx and the thin black marble pieces. Is it ok to use different grout color in center accent row than the color of the grout used on the porcelain on the sides?

        3) I installed a piece of schulter trim on side of porcelain tile intended to be used as trim between it and the mosaic accent in the center. I installed flat against the porcelain using 254 platinum thinset. No part of the trim installed behind the porcelain. I am considering removing the trim. Any suggestions how to remove it without damaging the porcelain?

        Reply

        • It’s my belief that honey onyx tile, in any shape or form, is a bad idea in a shower. But we’ve talked about this and I understand that it’s important to you and that you are really trying to come up with a way to move forward with it. Additionally, no matter what tile is chosen, any water that may, or may not, get behind the tile shouldn’t penetrate into the wall cavity assuming the walls are properly built and waterproof.

          With that in mind, I think grouting with Flexcolor would be the simpler, more effective, and give a better appearance than using silicone. However, I believe either would work. The best product I have found for cleaning silicone is denatured alcohol but you have to use it while it’s still wet. But I’ve never used, nor heard of DSR-5 and don’t know how that would work.

          But grouting with a non-cement grout like Flexcolor and using a good sealer is probably going to be your best bet. The best stone sealer that I know of is Stain-Proof by Drytreat (affiliate link). Judging by the price tag it had better be good. 😉 https://amzn.to/2NdwYuV

          With non-cement grouts I don’t think you’ll have any issues with the color being different. They don’t bleed like cement-based grouts do. But, as always, testing beforehand is your best bet.

          For the Schluter trim, it sounds like you installed it so that it tucks behind the center mosaic as opposed to tucking behind the porcelain tile? As long as you have access to the center mosaic part of the wall then you should be able to pull it straight out. I would start with getting a putty knife behind it and loosening it from one end. I would not expect to save the Schluter strip. Hopefully, I understand this but I’m not sure that I do.

          If the flange is tucked behind a tile and it’s installed with 254 then I wouldn’t expect to be able to remove it without damaging something (possibly everything it’s touching). I’m sure you’re aware, but 254 is really strong mortar.

          Reply

          • Since I submitted previous post, I called Miracle Sealants technical help desk and asked if any of their products would prevent water from seeping into groutless mosaics and the rep. said their H20 plus sealer would do that because it’s water based. I couldn’t tell from google search if Dry Treat is water or solvent based. I’d prefer to use sealer only without grout because if I don’t get all grout removed from the black marble trim will be very difficult to remove after it dries.because of the wavy shape of it. Do you think rep. is correct that water based sealer without grout will keep water from seeping in between the tiles? If you don’t agree, then I’ll buy solid pencil tiles to use for the trim. Thanks.

          • Essentially, the purpose of the sealer would be to take the place of grout or another kind of sealant. This isn’t what sealers are designed for but I’m not going to outright say that it wouldn’t work. If it was in there thick enough then it could.

            Additionally, I don’t know why a water based sealer would work better than a solvent based. I’m not sure if it has something to do with the consistency or with the clean up of it?

            So I would be skeptical of this method but real world testing is your best bet. I just can’t say that a sealer will do what you want. It would just be speculation on my part.

            One additional thought, solvent based sealers usually aren’t recommended with single component grouts like Fusion and Flexcolor. I know that Custom Building Products recommends their Sealer’s Choice Gold, which is water based, if used with their Fusion grout. I would guess that Flexcolor CQ is the same.

            So that’s something to keep in mind when figuring out which combination of products that you end up using. Drytreat Stain-Proof is definitely a solvent based sealer and has the smell to prove it.

  50. So, I’ve installed GoBoard around my tub per your YouTube video even using the mesh tape along the tub/backer joint. I sealed all of the screws and gaps using OSI QuadMax per Johns Manville approved sealant list. My main question is will the thinset stick to the sealant in the joints? Do I have to make sure I have a certain amount of each tile actually on the bare backer board vs over the sealant?

    I had read good things about Ardex X77 thinset but that may be overkill for a simple shower. Looks like if I go with any of your listed LFT thinsets I should be covered for anything large or small correct? We haven’t decided on 6×12 or 12×24 tiles yet.

    Thanks

    Reply

    • You absorbed a lot of the information and that’s a good thing!

      I’ve asked about this before with different manufacturers and they all say that it’s OK. As far as thinset, Ardex X77 is a great thinset mortar but I would agree that it’s overkill for normal porcelain tiles. If you are looking for an Ardex mortar I use X5 quite frequently and think it’s a great product. But I certainly wouldn’t steer you away from X77 if that’s what you want to use.

      Reply

  51. I’m repairing the bottom half of a 3’ x 4’ shower with 1’ bench. There is now Wedi board and I will reset the 4-1/4” x 4-1/4” white ceramic tile to align with the upper pattern (simple square grid). The tiles have been thoroughly cleaned of old mastic and grout. This is the first time I’m doing this, so I will be slow and meticulous. What thinset, trowel and procedure do you recommend?Thanks!

    Reply

  52. Hello Tile Guy,

    We’ve admired you, your patience, and dedication from afar for quite a while and now it’s getting closer to the beginning of our planned project — we wanted to check with you to see what you think about our thoughts on the types of setting materials and grouts that may be used to better ensure a good outcome.

    We’ll be using the large format 12″ x 24″ rectified porcelain tiles at two bathroom floors as well as at shower and shower over tub walls. We’ll also be using 4″ x 4″ tumbled travertine wall tiles at a kitchen backsplash. From speaking with a few retailers and reading through comments on your site, we ‘re thinking that Mapei Ultraflex LFT white thinset and Mapei Flexcolor CQ would be good setting and grout products to use at all floor and wall locations, possibly with 1/8″ grout joints for all as well.

    Do you think our inclinations are pointing us in the right direction for a successful install?

    We’re looking at Mapei products because the grout colors we’ve chosen happen to be from Mapei. Do you think unsanded Flexcolor CQ would be better to be used with the rectified porcelain floor and wall tiles, and that _either_ sanded or unsanded would be recommended for the Flexcolor CQ grout used with the tumbled travertine?

    We’re also wondering what type of leveling materials would be recommended for the rather new concrete slab at all of the locations.

    Also would Hardie backerboard be recommended at the shower wall and shower over tub wall locations?

    Is there anything else you might think of mentioning or advising us about to better ensure that the installation may be a quality, long-lasting one?

    Thank you again for all that you do for people who wish they had your experience!

    Kelly

    Reply

    • Yes, both Mapei Ultraflex LFT and and Mapei Flexcolor CQ would be good choices. You’ll want to use white mortar for at least the travertine.

      I’m not familiar with sanded and unsanded Flexcolor. I thought there was only one choice which was (sort-of) sanded. But I don’t see a problem with using Flexcolor for everything although you may want to use a sealer (water-based) or grout release on the travertine.

      For leveling products, it depends on how much you need to level and how deep but a self-leveling product from Mapei would work well along with Planipatch for smaller areas. Oftentimes, you start with the self-leveling product (with primer) and then fine-tune it with Planipatch.

      You’ll need a crack isolation membrane for any cracks in the concrete. Aquadefense is economical but Mapei has a sheet membrane that would work well also.

      Additionally, Hardibacker is fine and I’m assuming you’ll be waterproofing it with something. Aquadefense would work for this also.

      Thanks for your comments!

      Reply

  53. Greetings, Tile Guy,
    The chart is very helpful. I do have a question about thin set over a wedi shower pan when using glass tiles on the pan. Glass tiles are 1×2 on a mesh backing. The shower walls are a 4×12 subway tile. My question is should I use a glass thin set on the pan and a different modified thin set on the walls. It’s a very small shower area, 30×60. I also will be tiling the bathroom floor with a 6×24 porcelain over Shuluter-Ditra. I hope to use the allset thin set there, if I can find it locally. Which, it sounds like I might need 3 different thin sets, if the glass & subways need different thin set. Suggestions on thin set would be appreciated. Tile is bought, no turning back there.
    thank you so much.

    Reply

    • I don’t like glass tiles on a shower pan and I refuse to install them in this way for my own projects that I contract. There are too many potential problems for my tastes from semi-permanent darkening, mold, to safety issues (it is glass and they can chip and crack).

      In addition to this, I believe Wedi has a minimum tile size requirement of 2×2 inches. The reason for the requirement has to do with their point-load testing (too much pressure over too little space).

      So the tile may be purchased but it’s not installed yet. It’s not too late to cut your losses.

      But, to answer your question, you can use the glass tile adhesive on the shower walls if you wish. It’s more expensive to do it that way but if you have mortar left over then that would be a way to use it up. Also, you can use Allset on the shower walls.

      Reply

  54. Hello Tile Guy, thank you for the chart and responses over time – truly appreciated! Having trouble getting a concise response from stores and installers on how to install 16×16 tile outdoors on a fiberglass finished balcony that is over a living area. Do I have to coat with an epoxy adhesive of some type first or is there a thin set that will send ick to the fiberglass? Thank you!

    Reply

    • This is something that I don’t know the answer to. Your best bet is going to be to call the tech lines of thinset manufacturers and see if they have a product that will do what you want.

      You may want to look into the loose lay tile systems with adjustable pedestals.

      Reply

  55. I purchased dry treat for sealing the 12 x 12 honey onyx tiles. I thought they could be sealed on all sides, but the FAQ’s on their web-site says;

    “After a tile or paver is sprayed with one of our impregnating sealers on all sides, or dip-sealed (immersed in the sealer for a few seconds) it becomes water repellent. Therefore plain sand and cement mortar will have trouble sticking to it. There are polymer modified adhesives available which will work to over come this water repellency – and in fact benefit as mixing water loss due to capillary suction is effectively stopped. Dry-Treat have test results for 2 such sealers by popular brand Davco: 1) Davco SMP2010. 2) SE-7. An additive called Davelastic can be mixed with SE-7 for extra adhesion”

    I have already purchased use laticrete 254 platinum…does it have the same properties as Davco SMP2010 or SE-7, so it will stick to tiles with dry treat applied to the back, or should I only treat the front of the tiles?

    I plan to do the treatment with tiles laying flat before installing on the wall.

    Any other tips for using dry treat appreciated.

    Reply

      • I applied the drytreat last night to the onyx by dipping in a pan and wiping with a sponge. I should have read instructions on internet before using it. They say to apply a 2nd coat within 10 minutes, but I did not do that. Is it too late to apply a 2nd coat? If your answer is yes, I have a bottle of Miracle Sealants Impregnating Sealer…can that be used instead? I’m asking because I used up almost of the 16 oz. of drytreat on the 20 tiles, and that drytreat is expensive.

        Reply

        • I don’t see how a second coat a few days later is a bad thing. It might be ideal to do it within 10 minutes but applying it after that would still be a good thing, I would think.

          I would use up the Drytreat first before switching to the other sealer.

          Reply

  56. you know i use mortar all the time and in all that time i have been asked just what is Uncouplying ?
    Just what is ” uncoupling ? To me it almost means taking something apart but there is no info on what Uncoupling mean ?

    Reply

    • Great question! And I’d love to know the answer myself. This has been debated on the forums for a while. What exactly is “uncoupling” and why does one need it?

      There has been a lot of salesmanship with these membranes and a lot of people, pros included, misunderstand their capabilities. For me, uncoupling membranes are simply an underlayment for tile. Essentially, a substitute for cement board with some waterproofing capability as well.

      Reply

      • Here, I just dug out my Ditra manual, which explains :

        Uncoupling: tile has been successfully installed for thousands of years by incorporating an uncoupling layer, or forgiving shear interface, within the tile assembly. Ditra provides uncoupling through its open rib structure, which allows for in-plane movement that effectively neutralizes the differential movement stresses between the substrate and the tile, thus eliminating the major cause of cracking and delaminating of the tiled surface.

        Reply

  57. Any issue with using Schluter All Set over Goboard for the walls that will have 4×12 subway tile. I figured I was going to buy it for the ditra membrane on floor and if I can use if for the subway tiled walls too, that keeps things simple.

    Also would All Set work for 12×24 on the floor over ditra.

    Reply

  58. I installed a row of 5″ wide black porcelain tile at bottom edge of knee wall of my shower. The remainder of the 12″ tile is installed to top edge of knee wall. I noticed today that one edge of it is protruding out about 1/8″ due thinset uncoupling from the USG backer board. The other end of the tile appears to be adhered strong to the backer board. This piece of porcelain is 5″ x 12″. I haven’t installed the grout yet. It’s possible I could damage the surrounding tile if I tried to remove it, so would installing the grout (mapei ultraflex) be sufficient to keep the tile from coming loose (after I push it back flush with adjacent tile), or should I remove it and reapply with fresh coat of thinset? If your answer is to remove it, what is best way to do that without damaging surrounding tile?

    Reply

    • Typically, it’s best to remove it. If you tap on it- does it sound hollow? Can you push on it and get movement?

      The best way to remove is usually to sacrifice the tile that you are removing. Use a hammer and chisel and fracture the tile from the middle. If one end of it is loose then that end will likely come out easily.

      Reply

  59. MY contractor put in new plywood. I don’t know exactly what he did, but I do know that he used cement board and then used thinset to put in 48 by 48 porcelain tile. My grout is coming up and the tile is moving. My kitchen is an l shaped approx maybe 28 by 28 with tons of cabinets and Shaped island with granite. I called many tile stores and had 4 tile professionals inspect. All said that he should have done mud job. He wants to pull up and use epoxy and put back down. What do you think for now and long run? Did he do the right thing from the start and is this a good plan? TY! I am disperate!

    Reply

    • It’s hard to pitch a solution until you figure out the cause. So, simply suggesting epoxy mortar without knowing the problem doesn’t do anyone any good.

      The first thing to check is that your floor is capable of handling a tile load. If it can’t handle it then doing mud isn’t going to fix that problem.

      Over on the John Bridge Forum they have a Deflecto calculator. This will calculate the floor joists to make sure that isn’t a problem. You’ll probably need the help of your contractor to enter in the numbers that it needs.

      Next, is the floor joist spacing 16 inches? Is the plywood subfloor the proper type and thickness?

      If those things check out then it’s time to look at how the tile was installed. Was thinset put down underneath the cement board? Were the sheets staggered? Do the have enough nails? Are the seams taped with mesh tape?

      All these things are in the instructions for cement board which no one reads. I can tell you that not thinsetting down the cement board is one of the common mistakes people make and also one of the common causes of loose tiles.

      Lastly, would be the tile installation. Do the tiles have dust on the backs of them? Is the proper thinset used to install them (not the cheap stuff)? Is enough thinset being used? Is it spread on the floor too long prior to the tile being installed?

      So there is a lot of sleuthing to do but you should be able to build and tile a floor without having to use epoxy mortar or install a mud base. Those are solutions that are typically pitched by someone that doesn’t understand the cause of the failure.

      Reply

  60. I cut the first piece of honey onyx 12″ x 12″ tile for the shower project. Before I started cutting it, I wrapped a clear piece of waterproof tape on top and bottom of tile for location to be cut.

    After the cut the was made, the top and bottom surface on the side was chipped on the surface.

    I am using a new Kobalt 7″ wet saw blade.

    Would another brand blade be better to use? If so, which brand do you recommend? Any other suggestions to help prevent chipping?

    Reply

    • Chipping isn’t unusual per say and it’s hard to know if the chips are “normal”. It’s quite common to use sand paper or a diamond file to smooth the edges of the tile. I use diamond hand pads for this (affiliate link).

      You could also try changing the blade and with honey onyx you may even want to try a glass blade. Onyx is soft and the glass blade will cut it.

      Reply

  61. What grit# do you recommend?

    Also, to help prevent chips/cracking of the onyx tile after installed, would it look right or cause any problems if I installed a sheet of plexiglass over the honey onyx that will be installed in the center row of the shower wall? If your answer it would look ok and not cause any problems, would best way to seal it to the onyx is to use clear silicone? If not, what do you recommend?

    Reply

    • I typically have 100 grit as a standard and vary the pressure on it but, with as soft as onyx is, I think I would shoot for the 200-ish grit. You’ll probably still have to go lightly with it sometimes.

      For plexiglass, I really have no idea what that would look like. But I think clear silicone would be the way to go because it’ll match the best.

      Reply

  62. The reason I was going to cut the onyx tiles was to insert a piece of glass pencil tile between them. (2 cuts in each tile and a pencil tile between each piece), however, it’s too much work.

    A possible alternative I came up with: Glue 2 glass pencil tiles to each piece of onyx with clear silicone. How well do you think that would work in a shower? I do not expect any pieces would get knocked off or cracked due to minimal contact being in a shower, but if any did, they could be replaced/glued back on.

    If the above doesn’t work out, and I re-consider using the mosaic tile I was going to use originally (the ones with not enough room between them for grout)…would a sealer used for concrete sufficiently fill in the cracks between the 1/2″ tiles within the 12×12 tile?

    Reply

    • My experience with silicone is that the bond typically exceeds my expectations. This is assuming that I am compressing the materials together with little, or no, gap.

      However, concrete sealer isn’t something that I’ve worked with before and don’t know if it has a different consistancy or what it’s performance characteristics are so I don’t think I can be of much help with that product.

      I apologize for not responding sooner.

      Reply

  63. I’m a bit confused on which to buy still. I’m installing a 12×12 ceramic tile over Ditra, over wood. To bond the ditra to the wood, I’m supposed to use Mapei Porcelain Tile Mortar, and then to put the tile on top of the Ditra, I’ll need Mapei Uncoupling mortar, yes? Or would I use the Mapei uncoupling mortar for both applications?

    Reply

  64. Hi Just wondering if the Laticrete Glass Tile Adhesive will be OK to use for the taping part of the job over Hardiboard? or do I need to go purchase the Laticrete Gold? We will be installing ceramic floor tiles so I need to buy another thinset type for the flooring anyway.
    Any suggestions?
    Thank You so much. Your article really helped us in terms of when/where taping floating would be needed.

    Reply

  65. Hello, thank you so much for such a helpful post – first time attempting tile here and I have little knowledge of what is right and dont want to do something that will negatively affect the install down the road.

    I am writing about crack-isolation membrane used with premixed thin-set (MAPEI Premium Mortar Ceramic Tile Mastic (3.5-Gallon)). I installed this thinset and put the membrane on top of it, and then to my horror read that these two are NOT to be used together. It took several days to dry and I’m even concerned about the surface being level. I’m not at the point where I am ready to install tile over it – is that ok? What are the consequences you might foresee? This is in a bathroom.

    I’ve learned my lesson and for the 2 of 3 remaining bathrooms i’ll be mixing the thinset myself and using per your chart above. I’m just trying to figure out if I need to rectify the one I already started.

    Again, thank you in advance for your expertise. I have been pretty discouraged in the last week and felt at a loss for what to do – first time home renovations are not for the faint of heart!!

    Reply

    • I would remove the membrane and scrape up the mastic. Fortunately, you don’t have the tile installed yet and it’s only one room. That’s pretty fortunate! 🙂 The mastic shouldn’t be very difficult to remove.

      Reply

        • If you read the instructions for the products that you’ve selected they won’t list mastic as being suitable for that application. The mastic won’t dry properly and likely will mold. I’m sure there are other reasons as well. Feel free to reach out to the tech support of the products that you’ve selected and they can provide more information.

          Reply

  66. Wow! This is a popular and confusing topic.
    I cannot find the answer to my question.

    I needed to lighten gray mortar mix to repoint some cinder block fence joints. . I used 3 parts mortar mix and 1/4 part versabond thinset and it matched perfectly. Will this be a problem later or is it ok to mix thinset with mortar to tuck and point on a cinder block fence?

    Reply

  67. I am laying 1000’ of 24” X 48” porcelain tile in a new construction home. I have 1/4” Hardiebacker ready to lay down. The deflection rating of the floor is L/480. The floor appears to be very flat with a plywood subfloor.
    What would be best under the Hardiebacker and what would be the best mortar to use for my situation? What length and type nails should I use for this application?
    Thank you for all the great information.

    Reply

  68. I installed USG ultralight backer board in my walk-in shower. I seamed the joints good using the 5″ band USG sells. However, I did a terrible job on the inside corner because I could not get the band smooth when squeezing out the thinset underneath the band and had to remove it. I think I can do a better job if I used corner bead. Would vinyl or plastic corner bead be ok to use with USG ultra light backer board? If your answer is yes, Would it be better to use the kind with holes on the edges or without holes? Thanks.

    Reply

    • I don’t think it’s a good idea to use corner bead for the inside corner. The banding is how they want it done. I’ve seen it done with the sealant and mesh tape before but, as far as I know, that’s not an approved method by them.

      Reply

    • Great blog!! When I apply AquaDefense, is there a time limit as to when I need to tile? I thought I read some where it needs to be tiled w/i a few days. The mfg instructions has no details so I thought I would ask the pro!. I want to get the entire shower wall prepared then decide about tile, which now may be a few weeks considering we are all house-bound.

      Reply

  69. While removing ancient tile residue from cement backer board on the top of a tub surround, the board got gouged in spots. A small bit of wire shows in one place. I need to even off the surface before using AquaDefense, and then replacing the damaged area with porcelain tiles. What products would you recommend using under the moisture barrier and over it? I can order specialty items if necessary.

    I assume that I should use some mesh with thinset, but should this be modified or not? Do I need to use a band on the inside corners or would mesh be okay? This area gets light water exposure, but the previous PLASTIC tiles which I removed showed mold stains underneath.

    Reply

    • The gouging can be fixed with alkaline resistant mesh tape and a modified mortar. You can use the mesh for the inside corners, as well. Once everything is filled and flattened, you can paint on the AquaDefense over the cement board areas. Then install the tile with the same mortar that you’ve already used. If your porcelain tiles are 15-inches and under you can use a standard modified mortar like Versabond or porcelain tile mortar at Lowes. Otherwise, you’ll need an LFT mortar.

      Reply

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