Repairing Composites

Publish date:

When a single-skin fiberglass boat has a hole or severe gouge, the damaged fibers have to be replaced with laminates that match as closely as possible the construction of the original. This method attempts to duplicate the original laminate’s “physicals” to maintain its deflection, stiffness and continuity of loads.

The first step is to clean the surface, removing contaminants that may hinder the adhesion of repair laminates. A good start is a simple scrub using an abrasive pad with a strong kitchen cleaner that removes grease and wax. Next, because the materials being repaired have fully cured (sometimes for years), you must prepare the surface for a secondary bond. This preparation requires two things: enough surface area for a good, strong bond, and old laminate that’s been aggressively sanded with coarse grit.

The dry stack of repair laminates should match the original, but it is common practice to use a biaxial material with an integrated layer of mat as a replacement. Biaxial material adheres well and lends itself to contouring, or “drape,” and does a good job of dispersing loads in all directions.


Taper the repair surface around the edges to create a gradual transition for the loads affecting the repaired area. This taper should have a minimum ratio of 12-to-1 to ensure good bonding. Grind out the repair and contour the edges to match the shape of the hole. Check with a straightedge for an even taper. Make patterns for the new laminates using clear plastic or paper so each layer can be cut and numbered for sequence.

Repair resins have different characteristics that suit different applications. Epoxy resins provide superior adhesion and work with all laminates, but they must be used on epoxy boats. Vinylester resins deliver good secondary bonding, and they finish with gelcoat easily and reliably.

A repair can be vacuum-bagged, but as laminates are compressed, the stack may have to be adjusted for finished thickness. Repairs can also be infused, but this is an advanced technique that requires specialized equipment and knowledge. n

This article originally appeared in the February 2018 issue.