Tile is the visible part of a shower renovation. Waterproofing is the part that determines whether the tile is still in good shape in ten years. The two are related, but they're not the same thing, and a lot of shower failures we've been called in to assess trace back to inadequate waterproofing rather than any problem with the tile itself.
What waterproofing actually does ¶
A shower or tub surround is a wet environment by definition. Water gets behind grout joints, especially in steam showers or showers used multiple times a day. The waterproofing layer, installed behind the tile substrate, is what prevents that water from reaching the framing and subfloor. Without it, or with a compromised version of it, water migrates into the wall cavity and floor assembly over time, producing mold, rot, and eventually structural damage.
TCNA standards and what they require ¶
The Tile Council of North America publishes installation handbooks that define best practices for tile installation in wet areas. TCNA-compliant waterproofing for a shower typically involves a sheet membrane or liquid-applied membrane over the substrate, with fabric reinforcement at corners and seams. The membrane is flood-tested before tile is installed. We follow TCNA standards on every shower and tub surround we build. It adds a day to the schedule and a modest cost to the project, and it's not optional.
Common shortcuts and what they cost ¶
The most common shortcut is using standard cement board as the substrate without a separate waterproofing membrane, relying on the cement board's moisture resistance rather than a true waterproof layer. Cement board resists moisture but is not waterproof. Over time, water migrates through grout joints and into the board, which can cause the tile to delaminate and the substrate to degrade. We've removed tile surrounds where the cement board was saturated and the framing behind it was beginning to soften.
What to ask your contractor ¶
If you're getting estimates for a bathroom renovation that includes a new shower, ask specifically what waterproofing system will be used and whether it will be flood-tested before tile installation. A contractor who can't answer that question specifically, or who says the cement board is sufficient, is worth pressing further. The waterproofing system should be named in the written estimate.
Waterproofing is one of those things that's easy to skip because no one sees it. We include it on every shower and tub surround we build, and we're happy to walk through the process at the initial estimate visit. Contact us to schedule a walkthrough.