When a sheet is laid with a ripple, or not rolled firmly at a lap, the edge lifts into a small tunnel shaped like a fish's open mouth. Water follows the channel under the lap. The fix is to slit the wrinkle, lay it flat, and patch over it with a target piece extending a few inches all round. Inspectors look for fishmouths at every end lap and corner.
Got a fishmouth at every end lap on the north wall, slit them and target-patch before the board goes on.
Also heard as
- fish mouth
Related terms
Sheet membrane
Waterproofing supplied in rolls of factory-made sheet with a controlled thickness, joined at overlapping laps.
Shingle lap
Overlapping layers so each upper piece lies over the one below, sending water down and out like roof shingles.
Peel-and-stick
Field name for self-adhered membrane: rubberized asphalt or butyl sheet with a release liner on the back.
Detail coat
An extra reinforced layer of membrane at corners, cracks, drains and penetrations before the main coat goes on.