Bondline thickness matters: most structural adhesives perform best around 0.1 to 0.5 mm. Too thin starves the joint or leaves bare contact spots; too thick lowers stiffness, adds internal stresses and can trap voids. Thickness is controlled with fixtures, shims, spacer beads, scrim in film adhesives or controlled squeeze. Inspection checks for voids, porosity and uniform thickness.
Bondline came out at 0.05 in the corners, they clamped it way too hard.
Over-clamping is the most common cause of thin bondlines; clamps only need to bring the parts into contact.
Also heard as
- glue line
- bond line
- BLT
Related terms
Spacer beads
Small glass or plastic spheres mixed into an adhesive to hold a set bondline thickness under clamp pressure.
Starved joint
A joint left short of adhesive, with bare patches or voids where the glue soaked in, squeezed out or never reached.
Squeeze-out
The excess adhesive that oozes out along the joint edges at clamp-up, read as proof the joint is full.
Gap filling
The ability of an adhesive to bond parts with a loose or uneven fit and still cure fully across the gap.