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Mesh Tape: Don’t skip this step

2 inch mesh tape
2 inch alkali resistant mesh tape is applied at every backer board seam and corner

Mesh Tape: Don’t skip this step

 

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.

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Alkali Resistant Mesh Tape

For tile backer board 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. What this does is tie the two boards together and help prevent flexing. It helps prevent one board 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.

4 inch mesh tape
4 inch and 2-inch alkali resistant mesh tape

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.

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For the thinset step, you should look up the instructions for whichever backer board that you are using. Typically, most any modified mortar will work. To install the thinset you can use the back side (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 tape 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.

4 inch mesh tape
4-inch mesh tape was used on the outside corners of these recessed boxes

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.

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8 comments

  1. 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.

  2. Do I need to tape and thinset where floor and hardiboard meet (floor is new pitched dry pack shower pan)
    Thanks

  3. 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.

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