How to Match Gelcoat Color for Small Repairs

Wash with boat soap and water, rinse and let it dry. Then use rubbing compound and polish on a patch about a hand's width around the damage. West Marine and Practical Boat Owner both make the same point: oxidized, chalky gelcoat hides the true color. If you match to the chalky surface and then buff the repair, it won't match anymore. See hull-cleaning-waxing for how to remove oxidation without burning through.

Many builders record a gelcoat color name or code for each model year. Try these, in order:

• Your owner's manual, build sheet or a sticker inside a locker or console.
• The builder's customer service or owners club. Have your hull identification number (HIN) ready.
• Gelcoat suppliers that sell colors matched to builders and years. Some ask you to confirm the code with the builder yourself.
• A fiberglass supply house that matches a sample: some will match a paint-store color chip or a small chip of your old gelcoat (Fiberglass Warehouse, for example, asks for a piece at least the size of a quarter, and says it can also match a paint-store color chip you pick to match the hull).

A factory-matched gelcoat is the best starting point, but it matches the new color. On an older boat you will usually still need to adjust it.

Compare colors in daylight, outside, not under shop lights or a yellow garage bulb. Look from several angles and distances. Overcast daylight is easier to judge than harsh midday sun. Note that gelcoat on a sunny side of the boat may have faded more than on the shady side, so compare right next to the repair.

Shake or stir the gelcoat can well first so the solids are mixed. Pour out a small, measured amount into a clean cup. Write down how much. TotalBoat suggests mixing more than you think you need (it suggests at least a pint even for small jobs) so you have the same color later for touch-ups. Untinted, uncatalyzed gelcoat keeps for a while if sealed and stored cool; check the label for shelf life.

Dip the tip of a toothpick or stir stick in pigment and add only a small smear at a time, then stir completely. For off-white, cream and beige hulls, the usual tints are black (to take off the stark brightness), yellow and brown. Practical Boat Owner's quick method keeps pigment to a small share of the mix, no more than about 10% by weight or volume, measured in a graduated cup; check your pigment maker's limit, since too much pigment can stop gelcoat from curing properly. It's easy to add more and impossible to take it out.

Write down every addition (number of drops or grams). Without notes, you can't repeat a good match.

Put a small dab of uncatalyzed gelcoat on a strip of masking tape stuck right beside the repair, or smear it on a white card and hold it against the hull. Judge in daylight. Wipe it off with a rag (and a little acetone on the rag, not your hands) when you're done. Adjust and compare again.

Once the wet mix is close, split off two or three small samples with slightly different tint amounts. Add hardener to each at the ratio on the label, spread them on index cards or scrap fiberglass, and let them cure fully. West Marine stresses this step: gelcoat changes color as it cures, so only cured samples tell you the truth. If you can, wet-sand and polish a sample the way you'll finish the real repair, because sanding and buffing changes how it looks too.

Hold the cured samples against the polished hull in daylight. Pick the closest one. Make the real batch using exactly the same pigment-to-gelcoat ratio from your notes. Only then add hardener, and only to the amount you can use within the working time on the label.

Apply and cure the gelcoat as described in gelcoat-repair: fill slightly proud, seal it from air if your gelcoat needs it, sand flush with fine paper, then compound and polish. Blend the polishing a little beyond the repair so the shine matches.

Look at the repair again a few days later in daylight. A slight mismatch is normal. A small spot of slightly different white is far less noticeable on a busy hull side than on a flat, smooth panel. If it's clearly off, you can sand it back and redo just the top layer with an adjusted mix.

The new gelcoat hasn't had years of sun. Some owners find a slightly-too-bright patch fades closer over time; others see it stay different. Don't count on it. Keeping the whole hull waxed slows further fading of both old and new gelcoat. Over the next season, check the repair along with the rest of the hull.

Put a strip of tape on the can with your boat name, date, base and exact pigment recipe. Store it sealed, cool and away from heat and flames. Keep a cured sample chip with it. Log the recipe in your BoatMend boat profile so the next repair takes minutes instead of days.