Waterproof Corners & Seams
Corners and seams are where most shower leaks originate. Proper treatment of these critical areas is essential for a leak-free shower that lasts for decades.
Quick Summary
Why Corner Waterproofing Matters
Buildings naturally move due to temperature changes, settling, and daily use. This movement is concentrated at corners and changes in plane. Without proper reinforcement, waterproof membranes will crack at these stress points, leading to water infiltration behind the tile. The damage often goes undetected until significant rot has occurred.
Critical Areas to Waterproof
Inside Corners
Where two walls meet (vertical corners) and where walls meet the floor or ceiling. These see the most movement.
Wall-to-Floor Transition
The horizontal corner where walls meet the shower pan or tub. Often the first place to leak.
Shower Curb
All corners of the curb need full fabric coverage. Water frequently pools here.
Pipe Penetrations
Around shower valve, showerhead pipe, and any other wall penetrations. Use pipe collars when available.
Shower Niche
Inside corners of the niche and where it meets the wall. Many corners in a small space.
Backer Board Seams
Any seams in the flat field should be taped and coated, though fabric is optional for flat seams.
Materials for Corner Waterproofing
Waterproofing Fabric/Mesh
Alkali-resistant fiberglass or polyester fabric that bridges corners and distributes stress. Available in rolls (cut to length) or pre-formed corner pieces.
Pre-Formed Corner Pieces
Factory-molded inside corners (like Kerdi-Band) that provide consistent coverage. Easier to install than cutting fabric. Available for inside corners and outside corners.
Pipe Collars/Seals
Pre-formed gaskets that fit around shower valves and pipes. Kerdi, Laticrete, and other brands make these in various sizes.
Step-by-Step Corner Treatment
Prepare Corners
- Ensure all surfaces are clean and dry
- Remove any dust or debris from corners
- Fill any large gaps with thinset (let cure)
- Corners should be as close to 90° as possible
Cut Fabric Strips
- Cut fabric strips 4-6" wide
- Cut to length for each corner run
- For vertical corners, cut full height strips
- Or use pre-formed corners if your system includes them
Apply Base Coat
For liquid membrane (RedGard, Hydroban):
- Apply generous coat of membrane to corner area
- Cover about 3" on each side of the corner
- Work the membrane into the corner with brush or roller
Embed Fabric
- While base coat is still wet, press fabric into corner
- Use brush or trowel to work out air bubbles
- Fabric should be fully saturated—no dry spots
- Smooth fabric flat on both sides of corner
- Overlap fabric strips 2" at intersections
Pro tip: Work in sections. Apply membrane to one corner run, embed fabric immediately, then move to the next. Don't let membrane dry before embedding fabric.
Apply Top Coats
- Let first coat dry completely (follow product directions)
- Apply second coat over fabric and surrounding area
- Apply in perpendicular direction to first coat
- Third coat may be needed for full coverage
- Final thickness should completely obscure fabric weave
Treat Pipe Penetrations
For pipes and valves:
- Use pre-formed pipe collars if available for your system
- Or cut fabric with hole slightly smaller than pipe
- Stretch fabric over pipe (it should grip the pipe)
- Apply membrane generously around penetration
- Build up multiple coats—these areas are vulnerable
Common Mistakes to Avoid
- ✗Skipping fabric in corners (membrane will crack)
- ✗Letting membrane dry before embedding fabric (won't bond)
- ✗Not overlapping fabric at corner intersections (gaps form)
- ✗Thin application that doesn't fully cover fabric (weak spots)
- ✗Forgetting curb corners (water pools here constantly)
- ✗Using drywall tape instead of alkali-resistant mesh