Quickly Trimming a Glass Layup

An easy way to prevent painful punctures to your fingers.


When adding a few plies of glass to an existing part, the fabric is usually allowed to overhang the edges. When cured the hardened fabric strands can form hundreds of spiky needles all around the perimeter of the part, just waiting to prick a careless finger (Fig.1).

Fig. 1: Sharp needles are ready to stab the unsuspecting builder.

You’ll need to trim the spiky excess somehow, usually with a saw or shears, then a sanding block. If you’ve let things get this far, wear gloves…but there is an easier way.

Typical epoxy systems intended for laminating have a pot life of 1 to 3 hours and a cure time of 12 to 36 hours. Somewhere in the transition between gooey and rock hard the cure process will reach a stage at which the epoxy it is still soft and flexible, although no longer noticeably sticky.

To preclude potentially painful porcupine punctures, simply return to the job at the right time and use a razor blade to skim along the edge of the part (Fig. 2).

Fig. 2: A razor blade easily trims the glass during curing.

The excess glass fabric will cut with no more effort than slicing a square of soft cheese. The existing hard edge will guide the blade. The epoxy-soaked yarn needles are flexible and won’t harm your hands.

After trimming set the part aside for the remainder of the cure time. When fully cured it will take only a few moments with a hard sanding block to develop clean, straight edges.

Dan Horton says he is “just a homebuilder”. He has been a pilot more than 30 years and currently flies a custom RV-8.


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