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Thinset Decoded: Which Thinset to use | Infographic

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’s 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 that I am the most familiar with. 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.

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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 $30/ bag and should have ANSI 118.15 stamped on it. 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 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 nails. The nails 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. 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. My favorite is Prolite from Custom Building Products.

 

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

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75 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.

    • 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.

  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.

  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?

  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?

  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

    • 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.

  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

    • 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.

      • 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?

  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

    • 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.

  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

  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,

    • 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.

      Greenskin: http://amzn.to/2mvpp8x
      Eco Prim Grip: http://amzn.to/2lVDNFp

  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?

    • 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.

  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?

    • 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.

      http://www.custombuildingproducts.com/products/surface-preparation/surface-primers/mbp.aspx

      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.

  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?

  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.

    • 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.

  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

    • it was quickrete all purpose sand

    • 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.

      • 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

  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

    • 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.

  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?

    • 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.

  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

    • 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. 🙂

  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?

    • 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.

  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

    • 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.

  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

    • 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.

  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.

  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?

    • 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.

  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.

    • 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.

      https://laticrete.com/en/our-products/tile-and-stone-installation/anti-fracture/125-sound-crack-adhesive

      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.

      http://noblecompany.com/products/nobleseal-cis/

      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.

      https://www.diytileguy.com/movement-joints/

  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

    • 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.

      • 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.

  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.

    • 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.

  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

    • 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.

      • 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.

  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

  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.

    • 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.

      • 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?

        • 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.

  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.

    • 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.

  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?

    • 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.

  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?

    • 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.

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