Select Page

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.

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. Build the gelcoat up so that it is just proud above the surrounding gelcoat.
  6. 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.

  1. Start by use 400 grit paper to wet sand the cured gelcoat from side to side, then top to bottom.
  2. Then gradually use finer grits papers all the way to 600, 800, 1200 and 1500.
  3. Wipe all the residue off and buff with a compound polish at a slow speed.
  4. 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?

ColRegs when sailing single handed

  Don’t neglect the Colregs when sailing single handed Sailing single-handed represents several challenges for skippers, not least how to...

Essential Yachting + Power Boat Safety Briefing

Yachting Safety Briefing   Down below Lifejackets and harnesses - fitting, when to wear, clipping on Gas - risks,...

Boat engine cooling systems

Some boat engine breakdowns are unavoidable but those caused by lack of maintenance or regular checks can be avoided. Failure to maintain an engine’s cooling system is a well known example of this, so it is well worth spending time checking over the cooling system both when the boat is ashore and afloat.

Boat Engine Failure – what to check

Engine failure If your engine fails or is overheating there are a number of things to check immediately: • Air filter...

Boat engine basics

Boat engines come in all shapes and sizes and include inboards, outboards, petrol, diesel, electric and hybrid systems. Some engines are...

Safe Skipper – crew management tips

Effective crew briefings are a vital part of the good on-board communication that helps everything to run smoothly on a sailing vessel at sea, whether it is cruising or racing.

Marine toilets – care and maintenance

There are a number of different types of marine toilet, or heads. They fall into one of three categories – manual, electric and vacuum, the most common being the manual, hand pumped type. These have double acting piston-pumps which both discharge the waste and flush the toilet with sea water.

Sailing to windward – how to take advantage of wind shifts

For most sailors, sailing upwind is the most exhilarating point of sail as you tack your way to your destination. Sailing to windward is a bit like zig-zagging your way up a mountain road through a series of hairpin bends – great fun but also calling for concentration and hard work.

How to ensure your boat is in proper working condition

In this article Eva Tucker from Volvo Penta presents a handy check list of all the things that you need to check regularly in order to make sure that your boat is in a seaworthy condition. Including maintenance, safety gear and electrical checks.

Jester Challenge 2022 – Sailing single handed from Plymouth UK to the Azores: Part 7 – Motivation

Jester Challenge – A modern experiment in old-fashioned self-reliance, self sufficiency, and personal responsibility. This is the seventh of a 10-part post where solo sailor, Bernie Branfield, shares his first-hand account of his single-handed, 2022 Jester Challenge, from Plymouth, UK to the Azores, in his 26′ Invicta Mk2, Louisa.

Seacock maintenance

If seacocks are always left open and neglected they can eventually seize which will prove a serious threat to boat safety should a connecting hose fail and the seacock refuses to close. There are three main types of seacock – ball valves, cone valves and gate valves.

Marine diesel exhaust checks

You should inspect the exhaust system for corrosion damage regularly, especially around the injection bend. If you have noticed the engine exhaust smoking a lot during the sailing season this can also indicate a number of potential problems.

Top Ten Tips For Learning The ColRegs Boating Rules Of The Road

Colregs Boating Rules Of The Road Skippers struggle to learn and remember the ColRegs Yachtmaster and Day Skipper course...

Rewiring a boat – overcoming the challenges involved

Skippers need to have a basic knowledge of boat electrics, to avoid potential problems and to be able to solve them when they happen.

The VHF DSC Radio jargon buster

AIS - Automatic Identification System This system is used by shipping. It allows another vessel or coast station to use...

Five dangers a vessel may encounter at sea

What are the main dangers a vessel may face at sea and what should skippers do to reduce the risk of these happening?

Understanding your mast and rigging

The rig of a sailing boat is put under huge stresses and strains so it is important for inspections of a yacht's spars and rigging to be...

Passage Planning Advice & Safety for skippers

Passage planning helps you to: • Decide where to go • Calculate how long it will take to get there • Avoid bad weather •...

Sailing into fog – being prepared and staying safe

Most skippers will sensibly delay their departure, if fog is forecast. However, if fog begins to form when you are at sea it is important to be prepared, and know what precautions to take, to help make your vessel detectable or visible in fog and keep the crew safe.

Cleaning & polishing painted topsides

The gelcoat topsides of a GRP boat can be pampered and restored to their former glory relatively easily when it is ashore. Gelcoat is only a very thin outer layer of the hull, often less than 1mm thick, so you should avoid cleaning it with highly abrasive cleaners, or an-ything that could potentially damage its surface.

Understanding tides

If you are used to sailing in tidal waters, you will know that tides can be both a benefit and a hindrance to the sailor. In many ways,...

How diesel engines work

The basic principle of a diesel engine is less complex than that of a petrol engine. No spark plug or ignition system is needed, making the basic diesel engine a comparatively straightforward system that results in fewer faults and has lower maintenance costs than a petrol engine.

Marine engine electrical system

The typical basic electrical system associated with a marine engine includes a dedicated engine starting battery, a starter motor, a charger in the form of an alternator, a solenoid and some engine sensors and instruments.

Antifouling for leisure boats – Part 4

Applying antifouling. Antifouling is best applied on a dry, calm day. It is best to apply the antifouling in the middle of the day to ensure the hull is dry and as warm as possible.

Essential boat engine checklist

Boat engine checklist Engine oil level check Even if you have checked it previously, confirming the engine oil level is up...