Basic Guide to Minor Fibreglass Repairs

This guide outlines the general process for repairing minor damage to a fibreglass laminate. The materials and method required will depend on the original laminate, the extent of the damage and the intended use of the component. Large repairs and damage affecting structural, load-bearing or safety-critical components should be assessed by an experienced fibreglass repairer.

Preparation

Where the reverse side is accessible, a repair is generally laminated from behind the damaged area before the visible surface is filled and refinished.

Remove dirt, grease, paint and other contaminants using a cleaning product suitable for the laminate. Cleaning should be completed before sanding to avoid working contaminants into the prepared surface. Allow the area to dry completely.

Remove loose, fractured or delaminated material and sand the damaged area back to clean, sound fibreglass. Taper the edges of the damage and abrade the surrounding laminate to provide a suitable surface for the repair to bond to. Remove all sanding dust before proceeding.

If the damage includes widespread cracking, a soft or water-damaged core, movement around fixings or separation between laminate layers, seek professional advice before continuing.

Laminating the Repair

1. Support the damaged area

Where required, temporarily support or cover an opening from the finished side using suitable tape or backing material. This helps maintain the original shape while the repair is laminated from behind.

2. Prepare the reinforcement

Cut the required fibreglass reinforcement before mixing the resin. Prepare enough layers to rebuild the damaged area to approximately the thickness of the original laminate, with the edges staggered across the prepared surface.

Use reinforcement and resin that are compatible with each other and with the existing component.

3. Mix a workable quantity of resin

Measure and mix the resin and catalyst or hardener strictly in accordance with the manufacturer’s instructions. Prepare only as much as can be applied within the stated working time.

4. Wet the prepared surface

Apply a thin, even coat of mixed resin to the sanded repair area. Ensure the resin covers the complete prepared surface without forming excessive pools.

5. Apply the reinforcement

Wet out the first piece of reinforcement with resin and position it over the damaged area. Use a brush or laminating roller to work it firmly against the existing laminate and remove wrinkles and trapped air.

The reinforcement should be thoroughly wetted without leaving the repair excessively resin-rich.

6. Build the repair

Continue applying and consolidating the prepared reinforcement layers until the repair has restored the required thickness and shape. Check each layer for dry areas, wrinkles and trapped air before adding the next.

7. Allow the laminate to cure

Leave the repair undisturbed for the full curing period specified by the resin manufacturer. Temperature can significantly affect working and curing times, so do not rely on a fixed time or assume the laminate has cured because its surface feels hard.

Once sufficiently cured, remove any temporary backing and prepare the visible surface for finishing.

Filling & Finishing

Inspect the repaired area and sand away sharp edges or raised fibres. Any remaining low areas can be filled using a compatible fibreglass repair filler. Allow the filler to cure fully before sanding it to match the surrounding contour.

For a painted finish, apply a compatible primer and coating system in accordance with the paint manufacturer’s instructions.

For a gelcoat finish, apply a compatible, colour-matched gelcoat system using the surface-curing method specified by its manufacturer. Build the repaired area slightly above the surrounding surface where necessary to allow for final sanding.

Once completely cured, carefully sand the repair using progressively finer abrasives, then compound and polish the surface to blend it with the surrounding finish.