Waterproof substrate for tub deck
Posted by Sean Dawe, answer by Keith L. on November 01, 1998 at 12:44:55:
Thanks for the info on why to set the tub in mortar. (I must apologize for the use of improper terminology - I refer to drywall mud as "plaster")

Before I set the tub, though, I have to tile over the deck. The tub is a soaker style (5'x3' set in a 4'x7.5' deck) and I will be putting in a circular shower curtain. The deck substrate is plywood so do I need to somehow waterproof it? I read that you can cement a layer of tar paper to the deck and then put down thinset mortar as a bed. When set you would tile over as normal. I do not anticipate great amounts of standing water on the deck due to the use of the circualr shower curtain, so do I need to worry about making the substrate waterproof? Isn't it possible to make sure that the grout is more resistant to water movement by using epoxy grout?

(I must confess that I have already tried the tar paper/mortar combo and the tile bed is less than flat. It can easily be removed now but I am worried about what will happen in the future when removal is not so easy. Sean

This is what I did. I framed the tub deck out of 2X material, covered it with plywood, felt paper, then 1/2" cement board. Then I finished it off with tile set in thin set mortar mixed with latex admix (no water)on the horizontal surfaces and mastic on the vertical ones, and used unsanded grout. One other thing I did was insulated between the frame members with fiberglass to help hold in the heat and control the noise a little. Oh yeah I set the tub in mortar (portland, lime and sand) too, but I also cover the wet mortar with plastic so the tub wasn't stuck to the mortar so I can lift it out if I have to. Hope this helps. Keith L.

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