Shower tile failures are almost always waterproofing failures, not tile failures. The tile and grout you see are not waterproof — they’re decorative. The waterproofing membrane behind them is what keeps water out of your walls.
Why Shower Waterproofing Failed for Decades
Traditional shower construction used paper-faced gypsum backer (greenboard) covered with a plastic sheet vapor barrier, then tile with latex-modified thinset. This “wet area” construction was wrong in principle: water inevitably migrates through grout joints, behind the plastic barrier condensation forms, and the gypsum face paper deteriorates.
Walk behind any failed shower tile from the 1980s–1990s and you’ll see the evidence: black mould behind the tile, deteriorated paper-faced drywall, rotted framing.
Modern Waterproofing Systems
Schluter Kerdi System (most popular in GTA)
Kerdi membrane is a polyethylene fabric-reinforced sheet applied to cement board with unmodified thinset (critical: do NOT use latex-modified thinset with Kerdi). Applied to all surfaces that will be tiled, with Kerdi-Band at all corners and transitions.
Schluter also makes Kerdi Board (rigid foam substrate that replaces cement board entirely) and Kerdi Drain (matching drain for seamless membrane continuity).
Why it works: The membrane is on the face of the substrate — the tiled surface is the waterproofed surface. Water cannot reach the substrate or framing.
Wedi Board System
German-engineered rigid foam-core panels with integral cement-based face. Waterproof by itself (not just moisture-resistant). Joints taped with Wedi Jolly tape and Wedi Eck sealant. More expensive than Schluter Kerdi on cement board; less expensive than Kerdi Board.
RedGard (liquid-applied membrane)
Brush or roller-applied waterproofing. Applied to cement board before tile. Must achieve minimum 30 mil thickness (usually 2–3 coats). Labor-intensive to properly waterproof complex geometries (niches, benches, transitions). Budget option that works when applied correctly — many failed applications from rushed single-coat application.
What Toronto Building Inspectors Look For
Ontario inspectors on bathroom rough-in inspection check: cement board or equivalent in wet areas (not moisture-resistant gypsum in shower), proper membrane installation visible at inspection. Some inspectors ask for photo documentation of membrane application before tile is set.
Waterproofing system questions and contractor recommendations at home.renovation.reviews.
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