There are some aspects of tile installation that seem small or insignificant but they aren’t. They really have a big impact.
The way you treat your backer board seams is one of them. Doing them improperly can lead to big problems down the road. But these problems can be avoided by this one simple step.
Estimated reading time: 4 minutes
Alkali-Resistant Mesh Tape
For tile backer boards such as Durock, Wonderboard, Hardiebacker, Permabase, and others the seams between the board need to be treated with 2-inch alkali-resistant mesh tape.
Then a coat of thinset gets flat troweled over the seam.
Additionally, if you are tiling over drywall it’s perfectly OK to tape the drywall seams this way instead of using joint compound.
What this does is tie the two boards together and help prevent flexing. It helps prevent one board from flexing in a different way than the other board. It helps to make the walls that are to be tile more monolithic.
What happens if you don’t use mesh tape?
Sometimes nothing happens.
But I’ve walked into bathrooms where all the walls have cracks in them that follow the backer board joints.
Sometimes tiles will pop loose where there’s movement. Sometimes it allows an unimpeded way for water to get behind the board and into the wall.
It doesn’t cost very much extra to carry out this step. It doesn’t take very much more time. But it’s a necessary part of a successful tile installation.
What exactly needs to be taped and mudded?
Basically, a good rule of thumb is to tape anywhere two panels come together. In the photo above you can see that I’ve taped between the panels but also in the corners.
You can sort of fold and squeeze the tape into the corner so that there is still one inch on each side. Make sure the tape is tight into the corner. Otherwise, that can cause problems later.
You’ll want to tape where the cement board backer board meets the sheetrock wallboard. You can see in the photo that I even installed some around the plumbing fixtures where the cut left a gap.
For the thinset step, you should look up the instructions for whichever backer board that you are using. Typically, almost any modified mortar will work. To install the thinset you can use the backside (flat side) of a notched trowel for tile.
One downside to this is that sometimes the notches will catch the tape in the corners so you’ll just have to be careful. Personally, I’ve found that a 4-6 inch flat putty knife works great for working the thinset into the mesh taped seams.
If you are going to be applying a liquid waterproofing membrane over the wall then you’ll put some thinset over the screw heads also and flat trowel it flat with the wall. You don’t need to use mesh tape over the screw heads though.
Outside Corners
Outside corners can be difficult with 2-inch mesh tape. It’s hard to get the tape to fold over the corner and stay long enough for the thinset to set up.
They make 4-inch alkali-resistant mesh tape and this stuff works great. If you have outside corners to do then you may decide to just get the 4-inch mesh tape only and use it anywhere you would use the 2-inch.
If you can’t get your hands on the 4-inch stuff I’ve had success using two layers of 2-inch mesh tape for an outside corner.
I’ve done this by overlapping them maybe 3/4 of an inch so the tape ends up being about 3 1/4 inch wide total. It’s not as easy as one layer of 4-inch but it works if it’s your only option.
I felt that this was a simple thing but it’s important enough to warrant its own post. By skipping this step one could really mess up an otherwise good installation. I’ll have more of these types of posts down the road.
Cement Board installed on Floors
For floor applications where cement board is installed over a wood subfloor with a crawl space underneath please refer to this post.
Sealing a bathtub to the backer board
For information on how to treat the joint between a bathtub or shower and backer board please see this post.
I’m using hardiebacker and kerdi membrane for an upcoming DIY project. Will taping the seams under the kerdi leave bumps, or is the tape thin enough that it won’t have an impact? I’ll be using 12×12″ tile on the walls.
It could leave bumps and some of that would depend on how well you smooth the Thinset out.
The exact proper way to go about what you’re doing is to tape and mud the Hardibacker seams and then apply the Kerdi membrane. Many installers will choose to forego the mesh tape on the backer board because they feel the Kerdi membrane does this task also.
Do I need to tape and thinset where floor and hardiboard meet (floor is new pitched dry pack shower pan)
Thanks
Is it required? Probably not. But I think it’s a good idea. I started putting it in on all of my showers and it’s helped that joint to not crack.
Does cement board undergo thermal expansion? Is it wise to install the cement board with gaps in between, say 1/8 inch?
If this is the same stove pad that you mentioned before them you may not want to use cement board.
If your subfloor is concrete then you might look into a product like Ditra or Redgard uncoupling membrane. Or you can simply install directly to the concrete if there’s no cracks where your installing.
If it’s a wood subfloor then you can use any of the products mentioned: Ditra, Redgard uncoupling, or cement board. But you will definitely have to use one of them and not stick directly to the wood.
The stove pad I am applying the tile directly to the concrete, which is brand-new, small, and uncracked. The rest of the floor will be adobe. This is a straw bale house, of which there are quite a few around here in the Utah desert, and adobe floors are common. Do you have any experience with tile and adobe? I will be tiling over adobe in the kitchen.
My cement board question was actually in relation to a tub surround and bathroom wall. It’s more of a general question about installing cement board — should a little gap be left for expansion? Maybe it’s mentioned elsewhere in your blog, which I am working my way through but have not yet read all of it.
Thanks for your advice! Is there a way to get email notification of comments and replies?
It depends on the brand of cement board. One brand says to leave 1/8 inch gaps and another says to lightly butt the sheets together. I usually put a small gap in when I install cement board on walls.
And I don’t know anything about tiling over Adobe. If you find out what the proper way to handle it is if be interested to know.
Really appreciate your mesh tape information. I’m using Denshield in my shower and they call for mesh tape with thinset on seams and corners. My understanding is that this is for strength. In lieu of the thinset/mesh tape, can I use a membrane seam tape such as redgard or kerdi band with thinset? Or should I use both, one for strength and one for protection? Thanks
If you want to be safe then they way to go would be to use both mesh tape and then the waterproof seam tape. But I would think the waterproof seam tape would be fine by itself and would accomplish both tasks.
I’m intending to use Redgard on the cbu of my tub surround, but this comment about using waterproof seam tape, specifically kerdi band instead of mesh tape is something I was considering, but how would this hold up under the Redgard?
Would thinset have to be applied over the kerdi band after installation to ensure proper adhesion of the Redgard, or is adhesion of Redgard onto kerdi not a problem?
Also what would be the modified/unmodified thinset requirements for this application?
I’m asking as I was considering this combination of kerdi band and Redgard when I came across this thread, but haven’t really found anything in blogs regarding the combining of systems for waterproofing solutions.
Am i overthinking this? lol
Thanks!
I’m not crazy about the idea of using Kerdi Band over cement board seams with Redgard.
What I like about mesh tape is that you are following the manufacturer’s instructions on how to treat the seam. Also, mesh tape is completely encased in thinset making the cement board sort of monolithic. At this point, Redgard can be installed without interruption.
With Kerdi band, you’d be bringing in yet another manufacturer with another set of instructions. I’m not saying that it wouldn’t, or couldn’t, work but I guess that I just don’t see the upside.
I believe Custom Building Products has their own Redgard seam tape which is like red Kerdi band. At least they used to have this product. I’m pretty sure the instructions were to Redgard the walls first- then install the banding. I don’t see any advantage to putting Redgard on the outside of the already waterproof banding.
Just an opinion.
For wall installation, if leaving 1/8” gap between hardie backer boards, would it be better to
1. fill then gap with thinset
2. Tape the seam with alkaline resistant mesh tape (either right after thinsetting the gap or wait till it dried)
3. Work thinset onto the mesh tape.
4. Apply red Gard or hydroban on the entire wall. 2 coats.
5. Wait few days for waterproofing paint to fully cured before tile installation.
Let me know if this is the right approach.
Thanks again for your useful posts. Much appreciated your time.
Oops. After step 3. Need to wait for thinset to dry before applying Red Gard or Hydroban.
Yes in everything except that I don’t think it’s required to wait multiple days for the waterproofing to cure. Once it’s completely dry it’s ok to tile over.
Completely dry is indicated by the color changing
How long do you need to wait for the thinset to dry before applying Redgard?
I think you want to see the surface of it completely dry. So if there are any areas that are dark then it wouldn’t be ready. It’s usually the corners that take the longest to dry but that’s not a rule.
But once thinset has all turned the lighter color then it’s ready. That’s my understanding anyway.
Did you have to wait for the backer board-to-wall adherent to dry before you applied the tape and thinset? Or can you adhere the backer board to wall and then immediately tape and thinset the seams?
I’m not sure what you mean by adhere the backer board? If you have a foam backer board then those can adhere to a wall but I’m not sure that’s what you mean?
But as long as the backer board is in place then the seams can be filled with thinset and mesh tape.
Not sure if that’s helpful, or not.
I am laying down Durock cement backer board over plywood – Durock instructs to trowel thinset over the plywood, then place the Durock on it. I am wondering if I need to wait for the thinset under the Durock to dry before I tape and thinset the seams where the Durock meets. I’m wondering because I don’t want to wait 2 days to set my tile (one day for thinset under Durock to dry, one day for taped and thinset seams to dry). Sorry my question was confusing – hope this makes sense? Thank you!
Over a floor, there is no reason to let the thinset dry. It should be nailed along with thinset so there’s no danger of the board moving.
Just to clarify….. In my shower, I’ve used Durock and followed with mesh tape and thinset on all edges. Everything is solid. Once dry, can I just coat everything with two coats of RedGard, or should I also use membrane tape with the RedGard? (I have purchased Laticrete Waterproofing Membrane Fabric, but wondering if it’s overkill)
Thanks!
If the seams are taped as you described then I don’t see a reason for the fabric.
Unless you are waterproofing the pan with liquid also. Then I highly recommend using the fabric in the corners around the bottom of the pan and where it ties into the drain.
Not a bad idea to use the fabric around the whole pan and flash it up the sides if using liquid waterproofing for a shower pan.
You need to use a bspor barfier over adobe walls, then wite and apply a mortar bed . Then tile. I live here in new mexico and some cheapos havr the plasterers apply plaster then tile
That fails, the plaster breaks fown when wet, sfones melt when wet
Good input!
I taped the seams on my permabase walls and of course the first corner I did is too thick. I sanded it down some and the worst part is going to be behind a vanity, plus I have 2 bags of planitop 330, so it’s not seppuku time yet but it did get me thinking. I can shim and trim so the cement board is perfectly flat. Then I put tape on the seams and thinset over it which hopefully only adds a 1/32″. Trim around the window gets double layers of tape so maybe a bit more. Then I put fabric and redgard on the same corners which maybe ads another 1/32″. So now the edge regions of all the CBU boards are raised by 1/16″ or more. I found an ANSI standard (A108.02-4.1.4.3.1) that specifies substrate to be no more than 1/8″ out of plane in 10′ and 1/16″ in 2′ for large format tile (15″ or more). I’m doing 12″x12″ tiles so that sounds like my tolerance right there.
How flat do you realistically need walls to be for 12×12 tiles? Do I just find 1/8″ or more low spots with a 4′ straight-edge and bring them out with planitop? Use a thick layer of mortar to give tiles adjustability and rely on leveling system clips to keep them in line? I’m afraid I’ll have to planitop out most of a wall to match the embedded tape margins.
There can be a small amount of build up with taping the seams especially around the window, like you mentioned.
Industry standards for 12×12 tile is 1/4 inch in 10ft and 1/16 in 12 inches. So a little more leeway than with bigger tiles.
You’re probably ok to proceed with the amount of inconsistency that you’ve mentioned.
Two tips: mud a wider seam around the window. So instead of 2 inches wide to cover the tape maybe used a 6 inch trowel and feather it over a wider area.
Another tip is to use a damp sponge and wipe the thinset with it. Not immediately after but maybe 15-20 minutes when it starts to dry. That will really help to feather and thin the end of the seam.
Ok, thank you. What’s the standard for 6″x36″ plank tiles?
Also, I only have a 4′ and 6′ straight edges to work with. How does that 10′ requirement translate into that span?
Planks take kick it up to large format which is 1/8 inch in 10 ft.
Just do the best that you can. As you get things flattened out you can slide the straight edge over the floor and see how flat it is.
Personally, I don’t even own a 10ft straight edge. The biggest I have is 8ft and it rarely appears on the job. Most of what I do are bathrooms and the floor space may not even be 10ft. Plus, trying to navigate a 10 ft straight edge through someone’s home isn’t always a good idea either.
If you are flat in 6 ft and can move that back and forth and still be flat then you’re OK.
I have read multiple sites that recommend leaving a gap between the tub lip and where it meets the backer board. What they don’t show is what you do with this gap. Is it recommended to tape the seam between the tub lip and backerboard or just fill this area with thinset or silicone without tape?
Do you apply thinset to all seams where the backerboards meet (gap) and then apply tape and cover with thinset, or apply tape first and then cover with thinset ? I have read where peolple have done it both ways and was wondering if one method is preferred over the other.
This post covers it. Also, my GoBoard video demonstrates the method if you want to see a demonstration of it.
https://www.diytileguy.com/tile-tub-flange-gap/
Hi, I did all my taping and used the modified thin set over. I thought the seams looked flat but some of them looked buckled. Do I have to sand these flat? I think that my thin set was a bit too thin. I am afraid to add the red guard to a surface that is not completely flat.
This can happen if the mortar is too thin but you’ll want to get it flat before moving forward with waterproofing. You can use a scraper to flatten it but a brick, or similar, works really well also.
First time shower DIYer. I made the mistake of using acrylic mastic instead of thinset when applying tape to the seams of my cbu. Is that a fatal mistake?
If it makes a difference, this is a basement shower so won’t be used much.
Ok, but do you have to wait for taped joint covering to dry smooth before using trowel to install tile on top?
I’m certainly not crazy about the mastic but read the instructions for the brand of cement board. If they allow mastic then maybe you’ll be ok on it.
It’s best but I don’t think it’s required. The problem is that the tape can come undone during the installation process if the mortar isn’t dry so that’s why I think it’s best to wait.
I didn’t mesh tape the joints of the 1/2″ cement backer boards in my shower stall, and now have a coat of thinset over all the joints and corners before I realized the severity of the mistake. Could I tape now and finish with more thinset or mabybe use Ditra and hope that provides sufficient decoupling? It is a 3′ X 3′ shower stall.
Following up on my previous question as I’ve tried to figure out how bad my problem is. Ditra and other decoupling membranes seem to be for floors only? I was planning on using Redgard as a waterproofer. I notice that they say it acts a s a crack preventer also when applied in a thicker coat. Also using mesh tape in the corners and joints with the first coat of Redgard. Would this be a sufficient fix? Thank you.
I don’t know if mesh tape works the same at this point. It’s be a good question for the backer board manufacturer. I think it would since they encourage prefill prior to applying the tape.
But applying a product like Kerdi, not Ditra, would solve your problem and also waterproof your shower.
I would think this would work ok. The have a waterproofing fabric that would be good to use over the seams and in the corners. But mesh tape then Redgard should work fine.
With a dark background and black text makes it almost impossible to read this page.
I just had two big updates but I still see a white background. Can you give a little more info about what browser and device you are using?
Hi! I have durock in shower. I am going to use thinset Kerdi band for all joints. Can I skip the cement board tape and just use Kerdi band? I am using Redguard after.
Kerdi tape will perform the function of mesh tape so you should be fine.
Have 1/2 existing gypboard on walls, do I need to replace with green board or can I prime existing cover with 15lb felt and then use cement board for shower enclosure?
You can check with the cement board manufacturer but I don’t think they want that installed over gypsum. Rather, remove the gypsum walls and shim out the studs, if necessary. Then tar paper. Then cement board.
I have installed a Kohler cast iron tub and installed 1/2” Durock surround. In the tub instructions it says butt Durock to the flang and silicone it. And in the Durock it says leave a 1/4 inch gap so I left it. I am going to use Thinset and mesh tape the joints, then follow up with Redguard for waterproofing. Is it ok to silicone that gap between the tub and Durock then waterproof over it? Also if you mesh tape and Thinset is it Best to use seem tape in the waterproofing step as well?
Thanks
Yes, you can silicone the gap between Durock and the tub flange but I recommend that you waterproof first, then caulk.
If you tape all the seams and corners with thinset mortar as part of the Durock installation step then I don’t think you need to do it again during the waterproofing step.
I’m doing a shower stall which will have Kerdi as the membrane. Can I use modified thinset over the mesh tape — let it dry completely — then use unmodified thinset for the membrane. My question is if you can use unmodified thinset over the modified thinset for the Kerdi installation and have everything work.
Yes. I think you are using modified to tape the seams of the backer board so that’s installed according to their instructions and then installing Kerdi over it after that. That’s perfectly fine. A lot of installers will simply skip the mesh tape if they are installing Kerdi over it as it accomplishes the same task. But there’s nothing wrong with following the instructions to the letter and there’s no downside to doing what you are doing.
Hi,
I have a shower made of cement boards with two niches. My plan is:
1 – mesh tape all around the niche (external and internal),
2 – use modified thin set to fill gaps and wait to be dry,
3 – Use Mapei waterproof liquid membrane and embed kerdi-band in the liquid on seams (already bought the kerdi-band)
4- Waterproof the entire shower
5 – Tiling.
These steps make sense to you?
Thanks,
Sounds good to me. I’ve outlined those steps, with photos, in this post if you are interested:
Building a Custom Shower Niche from Scratch
On the outside corner, where the hardie backer board meets drywall, should I use regular metal corner bead? Or just try to wrap the mesh tape? Tile will end at the corner.
You want a metal drywall corner there.
Hi,
I have Hardiebacker on my shower walls and my entire floor. There is also Hardiebacker on the walls in the area where the freestanding tub will be (3ft up the wall). I would like to waterproof the area around the freestanding tub. So can I tape and thinset the joints between the walls and floor (all Hardiebacker)? And then apply Redguard? Is it even necessary to waterproof the walls and floor around a freestanding claw foot tub?
Thanks!
It shouldn’t be necessary to waterproof the freestanding tub if it will only be used as a tub. But you certainly could if you wanted to.
Hi. Do I need to tape the ceiling and wall joints before tile using new drywall and old ceiling?
If you’re not replacing the ceiling then I wouldn’t. It just makes for more work.
Thank you for this! I’m working on a spare bathroom ,and going though all motions,as I’ve read they should be done. I was unclear how many of these steps were actually necessary, vs which steps were overkill. You have helped me clear it up thank you.
Nine years ago we remodeled our bathroom. At some point (I can’t remember exactly when) the grout started to break up around the entryway, and it is now entirely gone around three 8”x8” tiles, which themselves have come completely loose.
I was able to see concrete board through the thinset and also could see an untaped seam that went directly under the loose tiles (with a corresponding crack through the thinset).
Is it possible to scrape the thinset off the exposed concrete board and tape the concrete board only where the tiles have come up? Would it matter if I did not tape the entire seam because it goes underneath the wall-hung vanity (which therefore can’t be walked on) and those tiles remain securely attached? Or should I pop them all up & retape the entire seam?
I’m trying to avoid pulling up the whole floor & subfloor because that’s above my ability level (I’m a DIY).
Thank you!
There’s nothing wrong with leaving the non-failing tiles alone. So, yes, you can do what you have outlined. I have a hunch the cement board probably isn’t mortared down and you’ll have to decide if pulling up a section of cement board is going too far. You might simply decide to add a couple of fasteners, tape the seam, and reinstall the tile.
Thank you!
And your hunch was right — once I got the dried thinset scraped off the cement board and could peer through the seam I could see the board hadn’t been mortared down. But I decided against pulling up the floor — I have neither the skills nor the tools for that kind of job (or the budget to hire someone right now). Instead I taped & mudded the two-foot long seam (the tiles are 11.5″ x 11.5″ — my eyeballing was way the hell off), and mortared the three loose tiles back in place.
My next question involves grout. I found the box of old grout originally used on this floor in the basement and saw it was unsanded, even though the grout lines are 1/2″, which could explain why so much of it failed even beyond the loose tiles. I dug out the old grout and, since it’s only a 5′ x 6′ floor, I replaced it with premixed Custom SimpleGrout to minimize waste.
Along one wall, there is a gap of 1/2″ to 3/4″ between the floor tile and wall tile. This gap had been filled with floor grout, which has cracked badly. I had planned to caulk that gap and had purchased Custom Sanded Tile Caulk color-matched to the new floor grout, but the more I read about caulking such a large gap, not to mention warnings about caulking over grout, I decided against it. But I still don’t know the best way to close such a large gap. Since I haven’t removed the existing grout in the gap, I couldn’t tell you what’s behind it.
Suggestions on how best to fill that gap?
Thank you!
The best way to fill that gap is to put a sliver of tile in there. Then grout the tile side and caulk the side with baseboards. The other products that you have aren’t really the best products. The acrylic grout will crack and is Simple Grout rated for 3/4 inch? You might try grouting it and see how that holds up. You might have to keep going over it until it looks OK.
Hi,
I just completed a bathroom tile project using 2 full sheets of 1/4 ” Hardie backer board. I only had one seam. I originally used thinset mortor with a mesh but removed the mesh. It created a hump
along the seam plus I had to sand down. This also created an uneven surface to lay the12″ x24″ tile
so I took the mesh out. This is a 5′ seam. Of course I filled the seam with thinset then sanded the
seam where it’s flat. Should I be concerned ? Thanks in advance.
It’ll probably be OK. Cutting out steps doesn’t guarantee a problem it simply increases the likelihood of them.
Hi,
I am a first time DYI-er planning to do a shower and tile project, and find all the info on your website great. I have a question similar to the one asked here. If I knew enough, your answers posted here may already answer my question too, but since I am a first time DYI-er, I can’t really be sure, so I hope you don’t mind my asking this similar question, which is, if I use durock backerboards in my shower, and if I want to use waterproofing fabric tape like this one
(https://www.amazon.com/XFasten-Fiberglass-Waterproofing-Anti-Fracture-Membrane/dp/B07BPH1Y3N/ref=sr_1_2?dchild=1&keywords=waterproofing%2Bfabric&qid=1591741931&s=hi&sr=1-2&th=1) with Mapei Aquadefense waterproofing membrane, will it be ok not to use mesh tape and thinset mortar between the boards and corners, etc? I’d greatly appreciate your response!
That looks like the kind where the waterproofing soaks through. If so, you’ll be fine without mesh tape as long as the seams are filled with thinset so there isn’t a void.
However, if you want to do everything to the letter, then you should install the backer board according to its instructions and the waterproofing to its manufacturer’s instructions. In that case, the manufacturer will usually want the seams in the cement board taped since that’s the instructions for their product.
I love your site! Keep up the good work!
I had a contractor who installed a ceramic floor on a cement board, did not tape the seams and did not use thinset on the seams. The mortar set in like a rock onto the cement board but all the ceramic came up with little to no mortar adhesion. I now have about 100sq meters of floor that has mortar stuck to it and I am wondering how to install the floor back in. This is a light frame structure with steal beams underneath. Removing the mortar is not really an option.
Wondering if you guys might have a good idea!
Thank you!!!
If you’re talking about reusing the tile the only way I’m aware of is to grind the mortar off of the back. It’s dusty and not fun but might save some money.
I had a question about taping backer board seams. I have my cement board glued down with thin set and used roofing nails. Now I see that I should tape the seams. Won’t taping the seams make the tile become unlevel?
Oftentimes the factory seams round down to help reduce any unevenness. Additionally, the amount of unevenness should be fairly insignificant as long as you trowel the mortar flat.
It was very helpful to find out I could use 2 layers of the 2″ mesh tape for the window as I could not get it to wrap around corner. A friend & I put the 3×5′ cement board vertically on the ends of the tub. What I removed was drywall installed horizontally to the back wall for the tile. At the edge where we plan to abut the cement board & drywall there is no upright. Would the 4″ mesh tape work there to prevent cracking or would silicone caulk?
FYI, my house was built in 1974 with less than quality construction.
I apologize, but I’ve read this several times and can’t understand what’s being asked. It’s this section in particular that I’m having trouble with “What I removed was drywall installed horizontally to the back wall for the tile. At the edge where we plan to abut the cement board & drywall there is no upright.”
Would you be able to reword it so that I might be able to understand the situation? Thanks
Thanks a lot for your post. Found it really helpful. Following you advice and putting the mesh tape to cover seams between cement boards and then applying a layer of a thinset (MAPEI Large Tile and Stone). Next, I am planning to apply MAPEI liquid membrane. How long should I wait for the thinset to dry before applying the membrane? I would appreciate your reply.
You want to wait until it’s completely dry which you’ll see by the color change. Wait until its all turned the lighter color. This is under 24 hours, btw.
I found your post very helpful but I have been having trouble finding a solution to my situation. I have a kerdi pan with cement board on the walls. Should I use mesh tape for the joint where the pan and cement board meets and then add the kerdi band over it. Or just use kerdi band and that’s it? Do I then use aquadefense only on the cement boards and not touch the kerdi at all?
Appreciate the help!
Just using the Kerdi band is fine. It’s not a huge deal if you get some Aquadefense on the Kerdi band.
Before you start taping, do you fill the 1/8″ gaps between cement board sheets with anything (caulk, thinset)?
Placing thinset mortar first, before tape, is technically the correct way. I find this method to be less user-friendly though because the tape will pull off of the joint easier. If you tape first, and then mortar, you do need to make sure that the mortar completely fills the joint. Good question.
Thanks! What about between the bottom edge of the cement board and the subfloor? I’m doing a mortar shower base and I thought I should fill the gap so the mortar doesn’t slide in the gap?
Yes, I think that would be a good idea to tape and fill also
Just so I’m certain on this. Embed mesh tape with thinset mortar in the joint between the shower wall cement board and the subfloor plywood?
No. You’d want to embed it between the cement board on the wall and the shower floor before it’s tiled. So, if you are doing a mud bed then I’d put the mesh tape right in the corner between the cement board and the top of the mud bed and mortar it in.
I’m using Hydroblok on my shower walls. Do I need to use mesh tape and thinset between the Hydroblok walls and my mortar shower pan? The original cement board was embeded in the shower pan, so now the new hydroblok with sit in the channel instead of on top of the mortar pan.
It sounds like you are embedding the Hydroblok panels into a mortar shower pan. If so, I wouldn’t think you would need mesh tape around the perimeter but I think it would be a good idea to add it. I add mesh tape around the perimeter to all of my showers that I build.
Is there anything wrong with filling the 1/8″ – 1/4″ gaps between cement board sheets with thinset and then taping and applying more thinset over the tape the next day? I’m not sure if the goal is to fill the gaps or just embed the tape to the two sheets.
That’s fine. The purpose of the tape is both of those things
Taping went really well!!! I took the thinset right down to the the tape, and feathered it out about 4 inches to either side of the tape. End result is you can clearly see the “grid” of the embedded mesh tape. I was going to put another thinset coat overtop and feather it out even more, but I’m now wondering if this is perhaps counter productive by adding to the buildup?
If it sticks out more than 1/16th inch, or so, then feathering it is probably a good idea.
hi my question is i have finished a shower in my basement walls with cement board also done the tapeing with fiberglass alkaline tape now i am ready to seal and cover the tape ,my problem is i have made several trips to home depot return product that was recommend by there staff and i got home read the label and some of the product would say to use on walls and floors in wet area in shower ,but when you get down to reading the fine print on the pail or bags it would give the type of material to be use on the ones that was recommend says does not bond to cement board to what i can see from hare is that most contractor and handy man is using the wrong product on customer project you might of seen lots of this with your experience so my question to you is what make or manufacture i should be looking for .thank you
Unfortunately, the wrong products are used all of the time. In this case, I’m not sure what your specific question is but normally you use thinset mortar, which is a dry good that is mixed with water, and you use that with the mesh tape and the cement board seams. You don’t want to use any premixed products that come in buckets and are ready to use for this step.
Why kerdi over hardie? Just use the kerdi tape. Or use drywall instead of hardie. That’s way over kill. Definitely don’t hardie, mesh, and kerdi. That would be insanity.
Tile industry standards call for a waterproof layer in addition to Hardibacker which will absorb water. Kerdi membrane is a nice way to waterproof over the Hardibacker
I am using hardibacker for our fireplace. I want to have a drywall smooth finish. What should I cover the corners and seams with (in addition to the alkaline resistant mesh tape)?
Can I put drywall compound on the hardibacker once I fill the seams and corners?
I would try to install drywall everywhere that will be painted and install Hardibacker underneath the tile portion only. It’s OK for the tile to lap onto the drywall so put the seam between drywall and Hardibacker underneath the tile.
I’m trying to figure out why the inside and outside corners need to be taped and mudded. Because there won’t be grout there anyway—you’re supposed to use silicone at plane changes instead of grout. (I do plan to use fabric and redgard in the corners, so I’m not talking about waterproofing, I’m talking about making it monolithic.) Sorry if this is a dumb question!
If you use the fabric seam tape in the backer board corners then you don’t need to use mesh tape. But silicone isn’t the right thing to use in the corners at the backer board level. It is the appropriate product to use once it’s tiled.
To be clear, when I say fabric I’m referring to either the seam tape, like Kerdi-band or other similar tape that is thinset on, or the thin mesh-type fabric that is designed to have liquid waterproofing soak through- similar to this Laticrete product.
Can mastic be used to fill the seams on backer boards with mesh tape?
Disregard…I used regular thinset mortar.