Guides · Building science
Bathroom Waterproofing in South Florida
Tile and grout are not waterproof. In a South Florida shower, the waterproofing is a continuous membrane behind and under the tile, tied into a correctly sloped floor and drain, and tested with standing water before any tile is set.
Why it matters more here
Water gets behind tile in every climate. What is different in South Florida is that the wall never gets a dry season to recover. Indoor humidity stays high for much of the year, many homes are built of concrete block that wicks moisture, and bathrooms often have modest ventilation. A small leak that might dry out between showers elsewhere can stay damp here for months, which is how mold and failing substrates start.
The three layers that keep a shower dry
Layer 1
Sloped base
The floor under the membrane falls toward the drain, usually at 1/4 inch per foot, so water never sits.
Layer 2
Membrane
A continuous waterproof layer on the floor and walls, lapped at every seam and corner.
Layer 3
Drain connection
A drain designed to bond or clamp to the membrane, so the water on the membrane has somewhere to go.
If any one of the three is missing, the other two are working against the odds.
Membrane types
Most modern showers use a surface-applied membrane directly behind the tile. Look for products that meet ANSI A118.10, the standard for load-bearing, bonded waterproof membranes for thin-set tile.
| Type | How it works | Good for | Watch for |
|---|---|---|---|
| Liquid-applied | Rolled or brushed on in coats, with fabric reinforcement at corners and seams | Complex shapes, niches, benches | Film thickness must meet the manufacturer's spec, usually checked with a wet-film gauge |
| Sheet membrane | Bonded to the wall with thin-set, seams overlapped and sealed | Consistent thickness, flat walls | Every seam and inside corner is a potential weak point if not lapped correctly |
| Foam board systems | Waterproof foam panels with sealed joints, used in place of cement board | Lightweight builds, fast installs | Joints and fasteners must be sealed with the system's own products |
| Traditional liner | PVC or CPE liner under a mortar bed, with a pre-slope beneath | Older method still used by some installers | The mortar above the liner stays wet; needs a working weep system at the drain |
We favour a bonded surface membrane in this climate because it keeps water out of the mortar bed entirely, so there is less material staying damp under the tile.
The details where showers actually fail
Niches
A recessed niche is a box cut into the wall, with four inside corners and a sill. The sill must slope into the shower, and every corner needs reinforcement. A flat niche sill that holds water is one of the most common failure points we see when opening old showers.
Benches
Built-in benches need to be waterproofed on every face, with the seat sloped toward the shower. Solid block or foam bench forms are preferable to framed wood in a wet area.
Valve and shower head penetrations
Every pipe that comes through the membrane needs a gasket or sealant collar designed for the membrane system. A bead of caulk around the trim plate is not waterproofing.
The curb and the door
The membrane has to wrap over the curb and continue down the outside face. With curbless showers, it extends out into the bathroom floor. Our walk-in shower installations carry the membrane well past the wet zone for that reason.
Glass fastening
Glass clips and hinges are screwed through the tile. Holes should avoid the lowest parts of the wall where water collects, and each one should be sealed.
The flood test
Before tile, the drain is plugged and the shower floor is filled with water to just below the top of the curb. It is left, typically for a day, and checked for any drop in level or damp patches outside the shower. It is cheap insurance: a failed test costs an afternoon, while a leak found after tiling costs a new shower. Ask any contractor whether they flood test, and whether you can see it.
Materials around the membrane
Waterproofing works best combined with materials that do not feed mold if moisture does get through. Our guide to mold-resistant bathroom materials covers boards, grouts and sealants, and the right tile choice matters too; dense porcelain absorbs almost nothing.
Common questions
Can you waterproof over existing tile?
Some coatings are sold for that purpose, but they do not address what is behind the old tile. If the existing shower is leaking or the backer is damaged, the reliable fix is to remove it back to the framing or block and build a new assembly.
Does the whole bathroom floor need a membrane?
Not always. The shower area always does. Extending the membrane across the bathroom floor makes sense for curbless showers, wet rooms and upstairs or condo bathrooms where a leak affects a neighbour.
How long should a flood test run?
Membrane manufacturers and local practice vary, but a flood test is commonly left for at least 24 hours with the drain plugged, then checked for any drop in water level or dampness outside the shower.
If your current shower has soft grout, loose tiles or a musty smell that returns after cleaning, it is worth having it opened up. See how we approach rebuilding a shower in Miami, from demolition to the flood test.