How do I build a proper shower pan with slope for drainage in a Vancouver bathroom?

A proper shower pan requires a waterproof membrane, a sloped mortar bed that directs water to the drain at a minimum pitch of 1/4 inch per foot, and a correctly installed drain assembly — and in Metro Vancouver's humid climate, getting the waterproofing right is the single most critical element of the entire bathroom renovation. While understanding the process helps you evaluate contractors and ask the right questions, building a shower pan is firmly in the "hire a professional" category for most homeowners.

The shower pan is built in layers, and each layer must be done correctly for the system to work. Here is how an experienced Metro Vancouver bathroom contractor builds a proper shower pan using the traditional mortar bed method.

The Mortar Bed Method (Pre-Slope and Membrane)

The process starts with installing the drain assembly at the correct height relative to the finished floor. The drain sits at the lowest point of the shower, and its height determines the slope of everything else. For a standard centre drain, the top of the drain grate should sit flush with the finished tile surface.

The pre-slope is the first layer of mortar applied directly over the subfloor (plywood on wood-framed floors, or directly on the concrete slab in slab-on-grade homes). This mortar layer is sloped at 1/4 inch per foot from the shower perimeter down to the drain. For a 3-foot by 5-foot shower, that means the mortar is approximately 3/4 inch thick at the walls farthest from the drain and tapers down to meet the drain flange. The pre-slope must cure for 24 hours before the next step.

The waterproof membrane is installed over the cured pre-slope. This is the most critical layer — the one that actually prevents water from reaching the subfloor and wall framing. In Metro Vancouver, the two most common approaches are:

Schluter Kerdi sheet membrane — a polyethylene membrane with fleece backing that bonds to the mortar with unmodified thin-set. Kerdi is applied to the pre-slope, up the walls to at least 6 inches above the showerhead height, and sealed at all corners and seams with Kerdi-Band. The drain connection uses a Kerdi drain flange that creates a continuous waterproof bond from the floor membrane to the drain body. This is the most reliable system and the most commonly specified by experienced contractors in Metro Vancouver. Material cost runs $4–$8 per square foot; installed cost is $8–$15 per square foot.

PVC or CPE liner membrane — a traditional sheet membrane that is folded into the pre-slope and stapled to the wall studs above the shower line. Seams are solvent-welded, and the membrane connects to the drain through a clamping ring assembly. This is the older method and, when done correctly by an experienced installer, provides excellent waterproofing. However, the seams and corners are more prone to failure than bonded Kerdi installations, and any puncture in the liner allows water through.

The final mortar bed (top slope) is applied over the membrane, again sloped at 1/4 inch per foot toward the drain. This is the layer that the tile is set on. It must be smooth, uniformly sloped, and properly cured before tiling begins.

Tile is then set over the final mortar bed using modified thin-set mortar appropriate for the tile type and substrate. Grout is applied after the thin-set cures (24–48 hours), and the entire pan is sealed where it meets the shower walls.

The wall waterproofing is equally important. Cement backer board (Durock, HardieBacker) is installed on the shower walls — never standard drywall or greenboard — and the waterproof membrane (Kerdi or liquid-applied RedGard/Hydroban) is applied over the backer board and lapped into the floor membrane to create a continuous waterproof envelope. In Vancouver's climate, any gap in this envelope allows moisture into the wall cavity where it will feed mould growth within weeks.

A properly built shower pan in Metro Vancouver costs $2,000–$5,000 for the pan alone (pre-slope, membrane, final slope, and drain assembly), before tile. With tile, the complete shower floor and wall waterproofing and tiling typically runs $5,000–$12,000 depending on shower size, tile selection, and complexity.

Why this is not a DIY project: The consequences of a failed shower pan in Metro Vancouver are severe and expensive. A leak that goes undetected for even a few months in Vancouver's humidity will cause subfloor rot, mould growth in wall cavities, and potential structural damage. The tear-out and rebuild costs $8,000–$15,000 — two to three times the cost of having it done properly the first time. A flood test (plugging the drain and filling the pan with water for 24 hours) is performed after the membrane is installed and before the final mortar bed, specifically to catch any leaks before they are buried under tile. Your contractor should perform this test and show you the results.