KERDI Shower System: Step-by-Step Waterproofing Guide

Why KERDI Wins

Traditional mortar-bed showers fail. Cement board over plastic sheeting fails. A properly installed Schluter KERDI shower is bonded waterproof, vapor-managed, and warrantied — when you follow the system.

This is the install sequence we walk Pro Desk customers through every week.

What You Need Before You Start

Step 1 — Substrate Prep

Frame your stud walls 16" o.c. Install your sloped shower tray (KERDI-SHOWER-T or built-up mud bed at 1/4" per foot slope). Hang KERDI-BOARD or cement board on walls, with the bottom edge sitting ON the curb and tray — never above and never below.

Step 2 — Set the Drain

Bond the KERDI-DRAIN flange to the tray with thinset. Press firmly. Wipe excess. Don't bury the bonding flange — it needs surface contact with the membrane in the next step.

Step 3 — Membrane the Floor

Trowel ALL-SET on the tray. Lay KERDI membrane fleece-side-down. Burn it in with a screed or grout float. Press it firmly into the drain bonding flange. Cut around the drain grate hole only.

Step 4 — Membrane the Walls

Walls first, ceiling last (if tiling ceiling). Cut KERDI panels to height. Trowel ALL-SET on the wall, comb in straight lines. Press KERDI in fleece-side-down. Use a screed or float to chase out air. Overlap panels by 2" minimum.

Step 5 — Seal Every Seam and Corner

This is where 90% of failures happen. Every seam, every inside corner, every outside corner, every pipe penetration must get KERDI-BAND or pre-formed Schluter pieces bonded over the top with ALL-SET.

Step 6 — Flood Test (Yes, Really)

Block the drain weep holes with a test plug. Fill the shower floor with 1" of water. Mark the water line. Wait 24 hours. If the water line dropped, you have a leak — find it and fix it before tile.

Step 7 — Tile

Use modified thinset (Schluter ALL-SET is approved for both substrate and tile side, which is why we recommend it). Set tile with the right trowel for your tile size. Maintain 1/8" minimum grout joint width. Use Schluter or appropriate corner trim where tile turns.

Step 8 — Grout and Seal

Epoxy grout (Laticrete SPECTRALOCK Pro) for high-end installs — no sealing, color-stable, stain-resistant. Cement grout for budget jobs — must be sealed.

Caulk the change-of-plane joints (wall-to-wall, wall-to-floor) with color-matched silicone (Mapei Mapesil T+ or Laticrete LATASIL) — NEVER grout these.

The 5 Failures We See Most Often

Catalog Products to Review

Full Schluter KERDI shower system — membrane, board, KERDI-BAND (5" and 10"), KERDI-KERECK corners, KERDI-DRAIN and KERDI-LINE, KERDI-SEAL pipe seals, KERDI-SHOWER trays and curbs, Schluter ALL-SET thinset, color-matched silicone. For grout, review LATICRETE SPECTRALOCK 1 pre-mixed grout and PERMACOLOR SELECT; confirm the exact product, color and suitability with the Pro Desk and current manufacturer instructions.

Bring your shower dimensions to the Pro Desk and we'll build the full materials list — no overbuying, no second trips.