Boat gelcoat and fibreglass repair: dings, cracks and osmosis
Quick answer
Gelcoat is the pigmented resin layer that protects a boat’s fibreglass. Chips, deep scratches and cracks should be repaired promptly so water cannot reach the laminate. A professional repair opens up the damage, fills it with gelcoat or epoxy filler, sands through the grits and polishes until colour and gloss match.
Why repair gelcoat early
Gelcoat is waterproof, but the fibreglass beneath is less so. A knock against the pontoon or a hairline crack around a fitting lets water into the laminate. Over time this can cause osmosis blisters, delamination or core damage.
Types of repair
- Light scratches: removed by compounding and polishing. See polishing and waxing.
- Chips and dings: opened, filled with colour-matched gelcoat and sanded.
- Stress cracks (crazing): opened in a V and filled; around fittings the mounting must be checked too.
- Structural damage: new fibreglass is laminated before gelcoating.
- Osmosis: gelcoat peeled below the waterline, hull dried, epoxy barrier and fresh antifouling.
We explain small repairs in how to repair boat gelcoat.
Colour matching
Gelcoat yellows in the sun. A good professional tints the gelcoat by hand so the repair is invisible, then polishes it to match the gloss of the rest of the hull.
Frequently asked questions
Can gelcoat be repaired with the boat in the water?
Repairs above the waterline, yes, in good weather and low humidity. Repairs below the waterline require hauling the boat out.
How do I know if my boat has osmosis?
Small blisters appear below the waterline and release a vinegar-smelling liquid when pierced. A surveyor or professional can confirm it by measuring hull moisture with a meter.
Gelcoat repair by port
Gelcoat repair: professionals by area
Related guides
How to repair boat gelcoat: chips, scratches and cracks
Step by step to repair chips and scratches in gelcoat, match the colour and know when the damage needs a professional.
How to polish and wax a boat so it shines like new
Wash, cut, polish and protect: four steps to restore gelcoat shine and keep it all season.
Boat maintenance calendar: what to do each season
A simple annual plan to keep your boat ready: what to check before, during and after the season.
Other maintenance services
Polishing & waxing
Polishing a boat removes the oxidised layer and fine scratches from the gelcoat using a rotary or dual-action polisher and abrasive compounds, followed by wax or sealant for protection. In the Mediterranean, polish once a year and wax twice a season.
View serviceAntifouling & haul-out
Antifouling is the paint applied below the waterline to stop algae, barnacles and other organisms sticking to the hull. In the Mediterranean it is usually renewed once a year during haul-out, when the bottom is also cleaned and anodes, propeller and through-hulls are checked.
View serviceTeak deck replacement
Replacing a boat teak deck means removing the worn timber, repairing and preparing the substrate, then bonding and caulking new natural or synthetic teak planks. It is usually needed when the wood is thinner than 4–5 mm, plugs keep popping out or water is leaking below. In Spain it typically costs €600–1,200 per m² for natural teak and €250–550 per m² for synthetic teak, depending on the boat and deck complexity.
View service