Punctured closed-cell backer rod releases gas that pushes up bubbles and blisters through a curing sealant bead. Damp or warming concrete pushes air and vapor up through fluid-applied membranes, causing pinholes. Prevention is careful rod installation, using open-cell or bi-cellular rod where needed, applying membranes when the substrate is cooling rather than heating, and filling bugholes.
Bubbles in the urethane every couple of feet, they jabbed the rod in with a screwdriver, that's outgassing.
Membrane crews in hot climates often coat in the late afternoon, once the deck is cooling, so air in the concrete is drawn inward instead of pushed out.
Also heard as
- out-gassing
- gassing
- bubbling
Related terms
Backer rod
A round foam cord pushed into a joint to set sealant depth and keep the sealant from bonding to the back.
Bugholes
Small surface voids in formed concrete left by trapped air bubbles against the formwork.
Fluid-applied membrane
A liquid waterproofing applied by roller, squeegee or spray that cures into a continuous rubbery film with no laps.
Holiday
A gap, pinhole or thin spot in a membrane or coating where it fails to cover the substrate.