Is RedGard liquid membrane good enough for a shower floor, or should I use a sheet membrane like Kerdi for better protection?

Both RedGard and Schluter Kerdi are code-compliant waterproofing systems for shower floors — but they perform differently, and for a shower floor specifically, the choice matters more than most homeowners realize.

RedGard (manufactured by Custom Building Products) is a liquid-applied, roller-on membrane that cures to a flexible, rubber-like coating. Kerdi is a polyethylene sheet membrane bonded with thin-set mortar. Both are accepted under Ontario Building Code for shower waterproofing, and both work — but the execution requirements and failure modes are quite different.

The Case for RedGard

RedGard's biggest advantage is that it's forgiving on complex geometry. A shower floor has a sloped mortar bed, a drain assembly, corners, curbs, and transitions — all of which are difficult to detail with a sheet membrane. RedGard can be brushed into corners, rolled over the entire floor, and feathered around drain flanges in ways that a sheet membrane simply cannot match. For a DIY-inclined homeowner doing a straightforward shower floor, RedGard applied correctly (two full coats, minimum 30 mils dry film thickness, bright consistent pink colour indicating full coverage) provides solid waterproofing.

The critical word there is correctly. RedGard's weakness is that it's entirely dependent on application quality. Thin spots, pinholes, missed corners, or inadequate coverage around the drain flange are invisible once tile goes down — and those are exactly the spots where water finds its way through. RedGard also requires a clean, properly primed substrate. On a traditional mortar bed shower floor, the surface needs to be fully cured and dust-free before application. Many shower failures attributed to "waterproofing failure" are actually RedGard applied too thin, applied over a dusty surface, or not properly integrated with the drain assembly.

The Case for Kerdi (and Why It Wins on Shower Floors)

Kerdi's advantage is consistency. Because it's a physical sheet, you can see exactly what's covered and what isn't. The Schluter system includes purpose-built components — Kerdi-Drain, Kerdi-Band corner strips, Kerdi-Fix sealant — that integrate the membrane, the drain, and the corners into a single engineered system. The drain flange is the most common failure point in any shower floor waterproofing, and the Kerdi-Drain is specifically designed to bond mechanically to the membrane, eliminating the gap where water typically infiltrates.

Kerdi also works beautifully with the Schluter-Ditra uncoupling membrane if you're tiling over a wood subfloor — a very common situation in Toronto's older housing stock, where post-war bungalows in Scarborough, North York, and Etobicoke have wood-framed floors that flex slightly. The uncoupling layer prevents tile cracking from subfloor movement while the Kerdi handles waterproofing. That combination is hard to beat in a GTA home with a wood-framed bathroom floor.

The tradeoff is that Kerdi requires more skill to install properly, particularly at inside corners and around the drain. The fabric needs to be embedded fully in unmodified thin-set (not modified — this is a common and costly mistake), with no voids or bubbles. Corners need Kerdi-Band strips overlapping correctly. It's not difficult for an experienced tile setter, but it's not a beginner project.

The Practical Recommendation

For a shower floor in a GTA home, a sheet membrane system like Kerdi is generally the stronger choice — particularly if your installer is experienced with the Schluter system, which most GTA tile setters are. The integrated drain system eliminates the most common failure point, and the physical membrane gives you visual confirmation of full coverage before tile goes down.

If your tile installer is more experienced with liquid membranes, a properly applied RedGard system with careful attention to drain integration, corners, and film thickness is entirely acceptable. The installer's experience with the specific system matters more than the system itself.

What you should never accept is a hybrid approach where someone applies a single coat of RedGard quickly and calls it done, or where the drain flange isn't properly integrated with whichever membrane is used. Ask your installer specifically how they detail the drain connection — that answer will tell you a lot about their waterproofing knowledge.

Need help finding an experienced tile installer or bathroom renovator in the GTA? Toronto Bath Remodeling can match you with local professionals through the Toronto Construction Network — browse the directory at torontoconstructionnetwork.com.