Fishmouths form when one panel has more slack or expansion than its neighbor, leaving an open, mouth-shaped gap at the overlap edge. A wedge cannot weld through one, so the bulge is cut, laid flat and patched with an extrusion weld. A seam full of fishmouths usually means panels were laid in the heat without enough attention to slack.
Heard on the job
Cut the fishmouth at station 120, lay it flat and patch it, don't try to run the wedge through.
Also heard as
- fish mouth
- fish-mouth
Related terms
Waves
Installer word for the wrinkles that form in a geomembrane as it expands in the sun.
Patch
Piece of geomembrane extrusion-welded over a hole, defect, destructive sample cut-out or failed seam section.
Fusion weld
Geomembrane seam made by melting the facing surfaces of two overlapped sheets and pressing them together.