In a tiled shower, the tile and grout are the finish, not the barrier. What keeps water out of the wall and floor is the waterproofing layer behind and under the tile, and it only works when the slope beneath it, the seams and the corners are done properly. Shower waterproofing is the part of a bathroom renovation that nobody sees afterwards, which is why it deserves the most attention before the tile goes on.
Why tile and grout are not the waterproofing
Tile is hard and grout fills the joints, but a tiled surface is a finish that sheds most of the water, not all of it. The layer that protects the structure behind it is a separate waterproofing membrane. An article in Construction Canada on avoiding waterproofing errors in showers lists common mistakes and is a useful read for anyone planning a new shower.
The same article notes that the Ontario Building Code expects a shower to be built so water cannot leak through the walls or floor, while the National Plumbing Code of Canada says little about how a shower is actually constructed. It adds that the Tile Council of North America Handbook bridges that gap.
What Ontario code guidance says about wall heights
Municipal building departments publish short guidance sheets on common problems. A City of Markham Builder Tip on waterproof wall finishes around bathtubs, revised in March 2015 and written for the 2012 Building Code, quotes Article 9.29.2.1 of the Ontario Building Code. It calls for waterproof finish to at least 1.8 m (5 ft 11 in) above the floor in a shower stall, and at least 1.2 m (3 ft 11 in) above the rim of a tub equipped with a shower. It also quotes Article 9.29.10.4, which calls for ceramic or plastic tile on these walls to be applied over moisture-resistant backing.
Those are heights for the waterproof wall finish. How high the membrane itself goes comes from the manufacturer's instructions, and Schluter, for example, says at least showerhead height. Check both the code height and the manufacturer's instructions for the product being installed.
The floor: slope comes first
Water has to run to the drain, so the slope under the finished surface matters as much as the membrane. Guidance from the Ceramic Tile Education Foundation, a US source, describes about 1/4 inch of fall per foot toward the drain. Treat that as general industry guidance, and ask your renovator which slope requirement applies to your project under Ontario rules and the manufacturer's instructions.
How the slope is built depends on the system. In a traditional assembly with a liner and a clamping-ring drain, the same source describes the slope as a sloped fill, often called a pre-slope, beneath the liner. A reply on that page notes that this layer is often not supplied by the plumber, so it is worth knowing who is responsible for it. Construction Canada lists a related mistake at the drain: leaving the weep holes in the drain base unprotected, which keeps water from draining through them. Other systems have their own instructions, so ask which type of system is being used and who builds the sloped layer.
The membrane: installed to the instructions
Each waterproofing membrane product has its own installation rules. As one manufacturer example, the Schluter Systems Shower System Installation Handbook says seams must be treated with KERDI-BAND or KERDI with a 2 in (50 mm) overlap, set in a Schluter thin-set mortar or an unmodified thin-set mortar. It says penetrations such as the showerhead and mixing valve must be sealed, and that the membrane must be installed up to the height of the showerhead at minimum. Those are manufacturer instructions for one product, not rules for every product. The handbook linked here is from Schluter's US site, so for a Canadian project the installer should use the Canadian literature for the product being installed. The practical point is simple: the membrane, the mortar and the substrate need to be a system the manufacturer approves.
Test before you tile
The same handbook strongly recommends a water test before tile is set, and says to wait at least 24 hours after the membrane is installed so the thin-set can set. Schluter's water test page describes marking the water level and holding it for a set time, with 24 hours typical. Other systems have their own instructions, so the installer should follow those for the membrane being used. A useful habit is to take dated photos of the marked level, so everyone can see it did not drop.
Common mistakes to avoid
- Not knowing which type of system is being used, and so not knowing who builds the sloped layer.
- Leaving the weep holes in the drain base unprotected, so water cannot drain through them.
- Leaving the openings for the valve or showerhead unsealed, or leaving seams that are not bonded as the manufacturer requires.
- Using mortars or other components that the membrane manufacturer does not approve.
- Setting tile before a water test has been done and recorded.
Questions to ask your renovator
Waterproofing is easy to promise and hard to inspect afterwards, so ask for specifics. Which membrane system will be used and on which surfaces? Which type of system is it, and who builds the sloped layer? How will the shower be tested, and for how long? How far up the wall does the membrane go? When you plan a project with our bathroom renovation team, these are the details worth settling before demolition starts, because they affect the order of work and the schedule.
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