A disk grinder roughens the strip where the bead will go so the extrudate fuses with clean polymer. Specs limit grinding depth to a small fraction of the sheet thickness, often 10 percent, require grind marks to run across the seam and be covered by the bead, and limit the time between grinding and welding. Deep or exposed grind marks are a classic starting point for stress cracks.
Grinding marks are showing past the bead on that patch, so cap it or redo it.
Grind across the seam, never along it, and only where the bead will cover; grind lines parallel to the bead edge are notches waiting to crack.
Also heard as
- grind
- seam preparation
- surface prep
Related terms
Extrusion weld
Geomembrane seam made by laying a bead of molten polymer along the edge of an overlap, used for patches and details.
Stress cracking
Brittle cracking of polyethylene geomembranes under long-term tension well below their yield strength.
Gun
Installer slang for the hand-held extrusion welder used on patches, boots and detail welds.
Patch
Piece of geomembrane extrusion-welded over a hole, defect, destructive sample cut-out or failed seam section.