Most homeowners focus on tile selection and fixture finishes when planning a bathroom renovation. Those choices matter, but the decision that determines whether the renovation holds up for five years or twenty-five is the waterproofing system installed behind the tile. This is the part of the project you will never see once the work is done.
What waterproofing actually does ¶
Tile is not waterproof. Grout is not waterproof. Water migrates through both materials over time, especially in a shower that is used daily. Without a continuous waterproofing membrane behind the tile, water reaches the substrate, which in most Toronto homes is cement board or drywall. Wet substrate leads to mould, structural damage to the framing, and eventually tile failure. A bathroom renovation that skips proper waterproofing will show problems within three to seven years. One that uses a proper system should last twenty years or more with normal maintenance.
The two systems we use most often ¶
The Schluter Kerdi system is a polyethylene sheet membrane bonded directly to the substrate with unmodified thinset. It is fast to install, easy to inspect, and compatible with large-format tile. We use it on most shower walls and floors. For shower floors specifically, we also use the Schluter Kerdi-Drain, which integrates the drain into the membrane system and eliminates the traditional mortar bed. The alternative is a liquid-applied membrane like Mapei Mapelastic or Laticrete Hydro Ban, which is brushed or rolled on and cures to a flexible waterproof layer. Liquid membranes are useful in complex geometries where sheet membrane is difficult to install without wrinkles.
What the building code requires in Ontario ¶
The Ontario Building Code requires waterproofing in wet areas including showers and tub surrounds. The code does not specify a particular product, but it does require that the waterproofing be continuous and extend a minimum of 150mm (6 inches) above the finished floor in wet areas. In practice, we waterproof the full shower enclosure from floor to ceiling, not just the lower portion, because water from a showerhead reaches every surface.
How to verify your contractor is doing it correctly ¶
Ask your contractor which waterproofing system they use and why. Ask to see the membrane before tile goes up. A reputable contractor will not object to this. If the answer is 'we use cement board and that is sufficient,' find a different contractor. Cement board is a stable substrate but it is not a waterproofing layer. The membrane is a separate step and it is not optional in a shower.
Waterproofing is not the glamorous part of a bathroom renovation, but it is the part that protects everything else. If you are planning a bathroom renovation and want to understand how we approach the waterproofing stage, reach us to schedule an estimate and we will walk through the details.