Step 6 · Waterproof Seams with Banding

This is the step most people slow down on. Take it one move at a time — there’s no rush, and you can rewind the clip as many times as you need.

This is the final and most critical waterproofing step. In a bucket, mix unmodified thin-set mortar with water using a mixing paddle on your drill, following the manufacturer's ratio until it reaches a smooth, peanut butter-like consistency. Using a V-notch trowel, apply a layer of this thin-set over the entire seam where the niche flange meets the wallboard. Cut your waterproofing band (e.g., Kerdi-Band) to length, ensuring you have enough for a minimum 2-inch overlap at all corners and seams. Firmly press the waterproofing band into the wet mortar using the flat side of your trowel. Use firm pressure, moving from the center of the band outwards to squeeze out all air bubbles and excess mortar, ensuring full embedment. The texture of the band should be visible. Immediately apply a thin skim coat of mortar over the top of the band to fully encapsulate it. Let this cure completely (typically 24 hours) before beginning to tile.