The Waterproofing Secret Every Homeowner Should Know Before Tiling a Bathroom

Most bathroom failures trace back to one moment: whoever tiled the shower didn't waterproof it correctly first. Here's what correct looks like.

The single most important step in any bathroom renovation is the one you'll never see when it's done: waterproofing. It goes in before the tile. It's hidden behind every surface. And it's the difference between a shower that lasts 25 years and one that develops mold, structural damage, and requires a full gut in 7.

I've opened bathroom walls that were tiled without any waterproofing. The tile looked fine from the outside. Behind it was black mold growing through rotted studs into the subfloor. The repair cost more than the original renovation.

Here is exactly what you should expect — and demand — from anyone you hire to tile your bathroom.

Contractor Tips

• Ask specifically: 'What waterproofing system will you use?' The answer should be a brand name — Schluter KERDI, RedGard, Wedi, or similar. 'We use the standard method' is not an answer.
• No drywall of any kind should exist in a wet area. Not moisture-resistant drywall (greenboard), not purple board. Cement board or a foam tile backer only.
• The shower pan (floor) is the most critical area. It must be sloped toward the drain at minimum 1/4 inch per foot and completely waterproofed including the curb.