Gelcoat Repairs

Gelcoat scratches and chips in a fibreglass boat are a fact of life! However, there comes a time when even the most hardened boat abuser starts to think about fixing things up a bit.

You may encounter damage such as extensive spiderweb cracks, chunks of missing gel or wear through to the glass laminate, all of which will need to be repaired.

The good news is that working with gelcoat is not as difficult as you'd think!

The four steps for making repairs are:

surface preparation
gelcoat application
sanding
finishing

If you follow these steps and are patient, you'll get good results.

Surface Preparation

Proper preparation of the damaged area is key to getting a good quality gelcoat repair.

The steps are as follows:

Firstly, chip away any loose material, and clear the gelcoat away so that you'll be applying new gelcoat directly to a stable substrate.
Next, sand with 150 – 220 grit paper. Using the sandpaper, continue to feather the edges of the prepared area. Work out onto the hull of the boat so that you've sanded a spot that's roughly rectangular and extends at least an inch beyond the damage.
Once you've finished sanding, wipe the surface of the repair with Acetone, making sure to remove all surface debris. Next, mask off the area around the repair. Make sure that your masking tape overlaps the edge of the sanded area, so that when you apply gelcoat, it will only be applied to a sanded surface.
Deep gouges and corner chips may require filling with topcoat mixed with colloidal silica filler. Allow to dry, and sand level with 200-300 wet and dry paper using a block, being careful not to sand too much of the original boat’s gelcoat.

Applying Topcoat

Colour matching is the most difficult part of gelcoat repairs. Colours always fade after exposure to UV. Here at CFS we have a large range of pigments and may be able to get close with one or two pigments mixed. You can send us a piece of the gelcoat or we can offer colour charts to get as close a match as possible.

For repairs, we recommend topcoat, which is gelcoat with a wax solution added. The wax will harden the surface, making it much easier to sand. We can supply this in pre-pigmented white or, if you are adding your own pigment, you must use clear topcoat.

First, the topcoat must be mixed with catalyst at 2% by weight.
Once you've mixed your topcoat, you have a certain amount of time that you can work with it.
Apply a first coat thick enough to fill the gouges, keeping in mind that the topcoat will shrink as it cures. Apply the topcoat so that it covers the prepared area and overlaps the masking tape.
Peel away the masking tape before the topcoat cures to reveal a clean edge. If you wait too long, the topcoat will harden completely, and you'll have to chip it away from the tape before you can sand. If you need to put a second coat on, you must sand the previous coat or it won’t stick.

Sanding

Once the topcoat is cured, you can begin sanding. This process is fairly straightforward, but there are a few tricks that will help.

Wet-sanding the repair with water speeds cutting and keeps sandpaper from clogging.
Ideally you will have wet-dry sandpaper in 320, 400, 600, 800 and 1000 grades.
Unless your repair is huge, you will only need one sheet of paper per grade.
It's essential to use a sanding block of some sort. Flatten the patch, then work on blending the edge in with the boat’s existing gelcoat. Finish with 1000 grit.

Finishing

Now you need to put the shine back. This can be done by hand, but for larger areas a low speed polisher with a lambswool pad will be required. 1000 grit scratches can be removed with Farecla G3, then complete the job with a finishing restorer like Crystal Glo restorer.