When a bathroom renovation fails, it almost never fails at the surface. The grout cracks, the tile lifts, or water finds its way into the subfloor, and by the time you notice, the damage is already done. In almost every case, the root cause is inadequate waterproofing behind the tile. This article explains what proper waterproofing involves and why it is worth paying attention to.
The two main waterproofing systems ¶
There are two approaches used in residential bathroom renovation: sheet membrane systems and liquid-applied systems. Sheet membranes, like the Schluter Kerdi system, are bonded directly to the substrate and provide a continuous waterproof layer under the tile. Liquid-applied systems, like Mapei Mapelastic, are rolled or troweled onto the substrate and cure to form a flexible membrane. Both work well when installed correctly. The key word is correctly: lapped seams, proper corner treatment, and full coverage are all critical.
Where waterproofing most often fails ¶
The corners are where most waterproofing failures happen. The joint between the floor and the wall, and between two walls, is where movement occurs and where water finds gaps. A proper installation uses pre-formed corner pieces or fabric tape embedded in the membrane at every inside and outside corner. Penetrations for drains and fixtures also need to be sealed carefully. These are not difficult steps, but they are easy to skip when a crew is moving fast.
Cement board versus drywall in wet areas ¶
Standard drywall should never be used as a substrate in a shower or wet area. Cement board (like Hardiebacker or Durock) or foam tile backer (like Schluter Kerdi-Board) are the appropriate substrates. Cement board is water-resistant but not waterproof on its own, which is why the membrane goes over it. We see a lot of renovation failures that trace back to greenboard drywall used in a shower, which holds moisture and eventually fails.
How long a properly waterproofed bathroom should last ¶
A bathroom tiled over a properly installed waterproofing membrane should last fifteen to twenty years without issues, assuming the grout is maintained and resealed periodically. Grout is not waterproof. It needs to be sealed every two to three years in a shower, and any cracked grout should be repaired promptly before water gets behind it. The tile and membrane underneath will outlast the grout by a significant margin if the installation was done correctly.
If you are planning a bathroom renovation and want to understand what our installation process looks like in detail, take a look at photos of recent work in our gallery or get in touch about your project.