Tile is the finish, the barrier sits underneath
Grout and tile are what you see, but what keeps water out of the framing and away from the ceiling below is everything we build under them. The Florida Building Code sets rules for the floor slope, the pan liner, the board behind the tile and a water test, and we treat each of those as a checkpoint before the next step starts. Nothing that ends up buried behind the walls gets covered before it passes its test and its inspection.
Slope: water has to reach the drain on its own
Your finished shower floor has to fall toward the drain at ¼ in to ½ in per foot, which the code writes as 2 % to 4 %. Across 4 ft of floor that is a drop of 1 to 2 in. With a curb, its top stays at least 1 in lower than the sides and back of the pan, so an overflow spills toward the bathroom where you can see it, not into a wall cavity. The code also keeps the top of the curb between 2 and 9 in above the top of the drain.
A curbless floor needs that same fall, so we lower or rebuild the subfloor to get it, and that takes more labor than a pan behind a curb. Low-curb and zero-entry layouts are covered on our walk-in and curbless shower page.
Liner or bonded membrane
Under the tile we use one of two barriers the code accepts. One is a sheet liner of PVC or CPE under a mortar bed. The other is a waterproofing membrane bonded to the backer and rated to ANSI A118.10. Whichever one goes in, it turns up at least 2 in above the finished curb and runs at least 2 in past the door jambs. Nobody nails or drills through it within 1 in above the curb, since one fastener there becomes a path for water.
On our jobs the floor and curb plus the walls get a bonded or liquid-applied membrane rated for tile, so the whole stall is sealed as one piece before any tile goes on. Inside corners, the valve opening and the niche get extra reinforcement, because seams and holes are where a membrane is thinnest.
What goes behind the tile on the walls
Behind shower tile we hang cement backer board or fiber-cement board; glass-mat gypsum panels listed for wet areas are allowed too. Regular drywall is out. So is green board, since water-resistant gypsum is still not permitted where the shower sprays it directly.
The code also wants a non-absorbent surface at least 6 ft up the walls of any shower or tub. When we are turning an old tub into a tiled shower, the membrane and the tile run to the ceiling, which clears that height with room to spare.
The flood test, before a single tile
We plug the drain, fill the pan and look for a drop in the water line, all before tile, because once the floor is tiled a leak only shows up as a stain in the next room or on the unit below.
Manufacturers also suggest letting a bonded membrane set for about 24 hours before the water goes in, since the seams are glued with thinset. The building official can ask to see the test.
Curing before the first shower
Plan on 3 to 7 days between grouting and the first shower, depending on the grout and setting materials we use. Miami humidity slows the cure, so we keep air moving in the bathroom and do not open the water early.
Where it fits in the whole job
Waterproofing lands in the middle of a remodel: after the plumbing rough-in and the backer board, before tile and glass. Our step-by-step remodel sequence shows where each inspection falls around it.
Frequently asked questions
Can you waterproof over my old shower tile?
No. A membrane needs a clean, flat backer, so we demo the stall to the studs or block, hang new board and build a new pan. Covering old tile would leave the original pan and liner in place where nobody can test or see them.
Is green board OK inside a shower?
Not where water hits it. Florida code rules out water-resistant gypsum in direct-spray areas, so cement board, fiber-cement or a listed glass-mat panel goes there instead.
How long does a shower flood test take?
The code test is 15 minutes with 2 in of standing water at the threshold. We usually leave the water in overnight, closer to the 24 hours membrane makers suggest, and check our mark the next morning.
How much slope does a shower floor need?
Between ¼ in and ½ in per foot toward the drain. Too flat and water sits by the glass, so we check the pitch with a level before the membrane goes on.
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