Repairing chips and dings in gelcoat

Sooner or later a GRP boat will receive the odd knock, chip or ding in its gelcoat. Boat owners need to decide if this is a job for a professional or it is something they can tackle themselves. This article might help you decide which would be the best option for you.

Gelcoat damage can be caused by a minor bump against a dock, an object in the water or even another vessel. When this happens it is usually not critical to repair it immediately, but if the ding has gone through the gelcoat, exposing the laminate beneath, then it will need filling with a temporary repair to stop water ingress, normally by using gelcoat filler.

Gelcoat repairs need to be done in temperatures of at least 18ºC otherwise the gelcoat will not harden off, so this is not a mid-winter job unless you can do it under cover in the warmth.

It is possible to do a decent looking minor repair yourself that will save you a chunk of money and be satisfying to do. First try doing a small gelcoat repair, get the hang of what is involved and move onto doing more challenging repairs. This is how to go about it:

1. Wipe down the area needing repair with acetone to remove surface dirt, wax and any contamination.
2. Remove any loose or flaking material with a sharp, V-shaped tool or a small grinding tool such as a Dremel with a burr bit. Be careful not to cut into the laminate.
3. Remove the dust and then wipe with the acetone rag again. Then mask up the repair, leaving about 4cm all around it.
4. Mix the gelcoat filler following the manufacturer’s instructions and apply it with a spatula, making sure there are no air bubbles. Build up the repair so that it stands proud of the surface.
5. Leave the gelcoat filler to cure, carefully peeling the masking tape away before it hardens completely. This may take several hours.
6. When the gelcoat has cured, rub it back using wet fine grade abrasive waterproof paper.
7. When the gelcoat is flush, cut it back with cutting paste until it is glossy. Finally finish it off with a layer of wax polish.
8. Done? The problem with this quick fix is that the colour of the repair will most likely not match its surroundings.

How to colour match gelcoat

You may have heard that colour matching a gelcoat is very difficult to do and best left to the professionals, but with a bit of practice at colour mixing, you should be able to get a satisfactory match. However, to get a 100% colour match takes years of experience and it is not realistic to expect that of yourself the first time you try it. It is better to try to get somewhere close and then blend the two colours using polish and wax.

Gelcoat as a base comes in three different colours – white, black and neutral.

• Black – use a black base if you want to match a dark colour such as a deep blue.
• White – use a white base for all lighter colours, not only different shades of white but also creams, pale yellows or pale blues.
• Neutral – the neutral base is almost clear and takes up the pure colour of the pigments you add to it, so it is used for strong, vivid colours such as a bright red, bright blue or green.

Gelcoat pigments

A basic gelcoat pigment set is all you will need and this should include a red, blue, black, brown and yellow. You will need these even if your boat has a white hull. There’s no such colour as pure white, but there are countless colours which come close.

Remember that gelcoat changes colour as it ages due to oxidisation. Consequently, as you walk around a boat the gelcoat colour will vary according to how much exposure different parts have had to sunlight and the elements.

Here are some basic steps to doing a colour match of an off-white gelcoat. Off-whites usually have tiny amounts of brown, yellow or black added:

1. Wet sand some of the gelcoat close to the repair with 1500 grit paper to get rid of dirt, grime and oxidisation.
2. Wipe the surface clean and add a thin layer of wax to bring the colour back.
3. Stir the base white gelcoat, un-catalysed. Measure some out into a mixing pot, enough to cover the repair. Keep giving it a stir every now and again.
4. Use wooden mixing sticks, one for each of the three pigments. Spread some pigment onto each mixing stick.
5. Add a tiny bit of black from its mixing stick to the base gelcoat and stir it well in. Dab a small spot of the mix on the clean gelcoat.
6. Little by little, add more colour to the mixing pot, testing as you go by dabbing a small spot of the mix near the repair.Think of this being like an artist’s palette. Add tiny amounts of the other colours, each timing mixing thoroughly. Be prepared for some trial and error and if it all goes seriously pear shaped, start again with a fresh pot. Keep doing this until you are satisfied you have the best colour match you can get.
7. Wipe the test swatches off using acetone.

You now have some coloured gelcoat that should be miles closer to the colour of your boat’s gelcoat than the base white colour. The next step is to apply the gelcoat, which entails adding catalyst to it and painting it on.

8. Use 150 grit paper and wet sand a few centimetres all around the repair in order that the new gelcoat can blend in with the existing gelcoat. Then wipe clean.
9. Give the gelcoat mix a good stir and then add the catalyst according to the manufacturers recommendations. This is usually in the order of 1% catalyst to gelcoat mix. Mix this very thoroughly.
10. Apply the gelcoat using a brush. Note that spray guns are used for major repairs and these are mostly done under cover in controlled conditions.
11. Paint the gelcoat on in thin layers, alternating with up and down brush strokes for one layer, then side to side brush strokes for the next.
12. Build the gelcoat up so that it is just proud above the surrounding gelcoat.
13. Leave the gelcoat to harden.

The gelcoat may take several hours to harden, so ideally leave it overnight and come back to finish things off the next day.

14. Start by use 400 grit paper to wet sand the cured gelcoat from side to side, then top to bottom.
15. Then gradually use finer grits papers all the way to 600, 800, 1200 and 1500.
16. Wipe all the residue off and buff with a compound polish at a slow speed.
17. Finally add a layer of wax and buff by hand for the perfect finish.

If all this doesn’t sound too daunting, why not give it a go if your next docking manoeuvre goes pear shaped?