Tile is not the waterproofing
Water gets through grout. It always has. Tile and grout are the wear surface, and what keeps the wall dry is the layer behind them. Cement board does not fall apart when wet, but water passes through it, so it still needs a membrane. Regular drywall and moisture-resistant green board do not belong in a shower at all.
The systems that work
| System | What it is | Watch for |
|---|---|---|
| Bonded sheet membrane | Waterproof sheet set over the backer, with a matching drain. Schluter Kerdi is the best-known brand | Seams must overlap and be fully bonded |
| Liquid-applied membrane | Rolled or troweled on in coats over cement board | Must reach the thickness the manufacturer requires; thin coats fail |
| Waterproof foam board | The board itself is waterproof | Every seam and screw has to be sealed |
| Traditional liner and mortar bed | Liner under a sloped mortar floor | Liner must sit on a slope, not flat. Not suited to curbless showers |
We use a bonded sheet system, Schluter or equal. Whatever the system, all parts should come from one manufacturer and be installed by its instructions. Mixing products is how warranties get voided.
Where showers actually leak
- The drain connection
- Inside corners and where the walls meet the pan
- Niches and benches
- The curb, especially where screws go through the top
- Around the valve and shower head openings
All of these are details, not big surfaces. A good installer spends most of the waterproofing time on them.
The flood test
Before tile, the drain is plugged and the pan is filled with water, then left for about 24 hours. If the level holds, the pan is tight. It costs a day and catches the one mistake that would otherwise mean tearing out a finished shower. Some cities inspect the pan or membrane on permitted jobs, so check with yours.
Questions to ask your contractor
- Which waterproofing system, by name?
- Does it cover the walls to full height, or only the pan?
- Do you flood-test, and can I see it?
- Are corners and changes of plane sealed with flexible sealant, not grout?
Phoenix homes sit on slabs, so a leak shows up as damaged walls and baseboards next to the shower, often long after the job is paid for. Waterproofing is included in every shower we build, from $7,900 conversions to $24,000 walk-in showers.
Key facts
- Required layer
- Continuous waterproof membrane
- Not waterproof alone
- Tile, grout, cement board
- Test before tile
- Flood test, about 24 hours
- Most common leak points
- Drain, corners, niches, curb
Related questions
Where we do this work
Services: Walk-In Shower Remodel · Tub-to-Shower Conversion
Bathroom remodeling in Phoenix, Mesa, Goodyear, and across the Valley.