Gelcoat is the hull's visible face and the laminate's first protective layer. A small chip looks cosmetic, but a repair made without first checking the structure underneath only hides the problem.
Diagnose first
- A single chip or scratch: usually superficial.
- Star crack: the mark of a point load or impact; laminate and core beneath are checked.
- Parallel cracks: can point to flexing or structural load; not filled until the cause is found.
Repair sequence
- Open up. The crack or chip is opened in a V; loose gelcoat removed.
- Check. Any wet or damaged laminate underneath is dealt with first.
- Colour match. Gelcoat paste is tinted to the boat; on old, sun-faded surfaces a colour difference is discussed in advance.
- Fill and cure. Filled slightly proud and cured with air excluded.
- Sand and polish. Progressively finer grits, then compound and polish.
Polish and oxidation
Dull, chalky gelcoat usually comes back with compound and polish. If the gelcoat is thin or crazed widely, topside paint is considered instead; its soundness is checked before painting.
What we often see
- Star cracks in gelcoat: Hairline cracks radiating from a centre around cleat and winch bases.
What gelcoat cracks tell you
Not every gelcoat crack means the same thing. Star cracks are usually the mark of an impact or point load; those around deck fittings can show the fitting flexing under load. Fine parallel cracks can point to an area where the laminate below is flexing. So before repair the cause is understood; a repair made without removing the cause cracks again in the same place.
Depth of repair
Damage confined to gelcoat is repaired with gelcoat or filler after the crack is opened and cleaned. If the crack reaches the laminate, the laminate is repaired first; gelcoat is the final layer. Sounding and moisture readings show how deep the damage goes.
Colour match
Gelcoat exposed to sun changes colour over time. New gelcoat, even with the right maker's code, may not match the old surface exactly. Colour is adjusted on a test piece and the acceptable difference agreed beforehand. On large visible surfaces, extending the repair to a panel edge makes any difference less noticeable.
Polish and protection
Dull gelcoat can often be brought back with the right stepped compounding and polishing. Each compounding removes some gelcoat; on thin gelcoat, too much can expose the laminate. A protective coat after polishing shields the surface from sun and keeps the shine longer.
When to paint
If the gelcoat is very thin, crazed over wide areas, or the colour difference has become unacceptable, painting may be the better answer. Paint needs different care from gelcoat; the decision is made with the boat's use in mind.
On survey
Gelcoat cracks are photographed with their location and shape; those pointing to a structural cause are graded separately.
Prevention
Good fendering, careful berthing and properly backed deck fittings prevent most gelcoat damage before it starts.
Cleaning and protecting the hull at the end of the season also reduces wear over winter, so spring polishing is lighter work.
After a repair, the surface is kept from direct sun and harsh cleaners for some weeks while gelcoat and filler fully cure; no polishing is done until the maker's waiting time has passed.
Patience here is part of a good result: a surface polished too early can lose its finish within the season.
Wait, then polish.
Good gelcoat care is mostly simple routine, done every season.