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Unread 10-26-2021, 12:09 PM   #8
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Join Date: Jul 2001
Location: Boerne, Texas
Posts: 94,455
Mock-up is a very good idea, Randy.

You wanna determine whether your code compliance inspector will accept drywall as a backing material for your mud walls. There is a lot of misunderstanding around the use of gypsum wallboard as a backing for mortar walls in a wet area. I don't believe that was intended to be excluded when the industry banned the use of drywall as a tile backing in such areas, but I'm told there are jurisdictions where you cannot even use it behind one-coat mortar. In unincorporated areas I'm perfectly comfortable with that application.

Stapling the metal lath to CBU doesn't work well in my experience. I generally used a slap-hammer to install my lath and when I tried that as a test on a couple brands of CBU I was not too successful. One more reason to use drywall. The "special" gypsum boards, such as your DensShield, I've never tried.

You're correct that your mud wall will be proud of your backing material. I learned to cut wood strips, usually rips of about 1/2" from 3/4" boards. Those would be tacked to the wall as a stop for the mortar wall and was used as the "float strip" in that area. Leaves you with a sharp, straight edge on your new wall. This, in the days mostly before my time, was covered with a "mud cap" or "radius bullnose" or "quarter round" tile, which was a commonly available trim for Glazed Wall Tiles. They're still available, but you don't see many folks using the style of tile that they go with these days. Google up A-4200 tile and you'll see what they look like.

The alternative is to use some sort of ceramic or stone trim piece to cover the edge of the tile and mortar.

My opinion; worth price charged.

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