KERDI-KERECK inside corners are pre-formed, factory-shaped waterproofing pieces that create a watertight seal at every 90° inside corner in your shower or wet area. They're made from the same KERDI membrane material as the sheet goods, but pre-shaped so you don't have to hand-fold KERDI-BAND — which is where most DIY waterproofing mistakes happen.

Each piece has two flat flanges that overlap the adjacent KERDI membrane by at least 2" on each side. Set it in thin-set mortar, embed the flanges, and the corner is permanently sealed.

Where inside corners occur in a shower

• Where two walls meet (vertical corners)
• Where walls meet the floor (horizontal corners)
• Where walls meet the ceiling (steam showers)
• Where the curb meets the wall
• Where benches meet walls

Why pre-formed corners matter

Hand-folding KERDI-BAND into a 90° corner creates wrinkles and air pockets. Air pockets = unbonded areas = potential water pathways. Pre-formed corners eliminate that risk. The factory shape is smooth, wrinkle-free, and makes full contact with the thin-set bed. For the small cost per corner, there's no reason to hand-fold.

Installation

• Apply thin-set mortar to both surfaces of the corner
• Press the KERDI-KERECK into the mortar with flanges fully embedded
• Smooth out air pockets — full contact is critical for waterproofing
• Overlap adjacent KERDI membrane strips by minimum 2" over the flanges
• Seal any remaining transitions with KERDI-BAND

Specs

• Material: KERDI waterproofing membrane
• Angle: 90° inside corner
• Flange overlap: Minimum 2" on each side
• Bond: Thin-set mortar (Schluter SET, ALL-SET, FAST-SET)

How many do you need?

Count every inside corner in the shower: typical 3-wall shower has 2 vertical wall-to-wall corners + 3 wall-to-floor corners + 2 curb-to-wall corners = 7 inside corners minimum. Add more for niches, benches, and half-walls. Always order a few extras.

Pairs with

• KERDI waterproofing membrane
• KERDI-KERECK outside corners (for outside corners and bench edges)
• KERDI-BAND sealing strips
• Schluter SET or ALL-SET mortar