So, it’s critical that the shower be waterproof.
Wheneverinstalling tilein any area of your house, you need a specialsubstrateor base layer.
Cement board comes both in 1/4-inch-thick and 1/2-inch-thick versions.
The Spruce / Liz Moskowitz
Even the slightest amount of movement in a building structure can telegraph to the tile and crack it.
When water leaks behind shower tile, the results can be devastating.
Best Cement Boards and Applications
There are several acceptable applications of cement board in the shower.
Then, the cement board is installed on top of the plastic sheeting.
Tile is laid onto the cement board with thinset mortar or mastic.
Fifteen-pound felt tar paper is sometimes used in place of a plastic moisture barrier.
No plastic sheeting goes behind the cement board.
Then, tile is installed over the membrane.
Waterproof sheet membrane, also called uncoupling membrane, is applied to the cement board with thinset adhesive.
One such brand of sheet membrane is Schluter Kerdi.
After the thinset has dried, tile is applied to the sheet membrane with thinset.
Using cement board and a sheet membrane is one of the more expensive applications for waterproofing a shower.
Georgia-Pacific’s DensShield is one such product.
Other unacceptable applicationslike drywallwere never used in the first place by professional tilers and contractors.
They were mainly used improperly by do-it-yourselfers.
Drywall
It takes just a little moisture for drywall’s paper facing to disintegrate and turn moldy.
Because paper is an organic product, it will quickly become moldy.
The solid gypsum core will then begin to crumble.
Drywall has never been an acceptable backer board for shower tiles.
Greenboard
Greenboard’s acceptability as a shower backer board is debatable.
Greenboard is only slightly more water-resistant than plain drywall.
Greenboard has drywall’s same gypsum core and paper facing.
However, the facing is impregnated with waxes that shed water better than conventional drywall’s paper.
But with many non-organic shower backer boards available as alternatives, there is little reason to use greenboard.
Plywood
Plywoodon its own cannot be used as a substrate under tile in showers.
This is not true.
Mold Cleanup in Your Home,EPA
