Steam-room grout passes vapor even when the glaze does not
Steam-room methods SR613 and SR614 in the Tile Council handbook list tile and setting materials that meet stated minimums. Ceramic tile used there should meet ANSI A137.1 and be recommended for steam rooms by its maker. After materials are chosen, the FAQ says to follow that maker's own procedure.
Why a membrane is in the assembly
Glazed tile is vapor-impermeable. Cement grout is not. It readily passes water and vapor, so vapor can move through the joints. The wall cavity may also need insulation because the two sides of the wall are at different temperatures and can condense. The membrane should meet ANSI A118.10 and be rated by its maker for a steam room. It bonds to the substrate, and tile can bond to it. It is not a coating made for foundations or wood decks.
Board and membrane order
For thin-set detail SR614 the FAQ says a waterproof membrane can go on top of cement board or behind it. Some manufacturers require one of those positions. Their instruction overrides a general reading of the detail.
Source
Fetched 2026-10-11 from Tile Council steam room FAQ. The sentences above follow that page. They are not a contractor promise.
Related notes
- Tile notes index
- Shower methods B421 and B422 leave the backing choice to the makers
- Exterior tile has to drain before water sits in the joints
- Shower photos
Send photos if you want another person to look at the area. This note does not set a response time.