Mistakes that burn gelcoat

The short version: Gelcoat is thin, and compounding removes some of it every time. Most burn-through comes from too much pressure, heat, or time in one spot, from edges and corners, and from skipping a check as you go. Work in small sections, keep the pad moving, and stop as soon as the color looks see-through.

On this page: What "burning" means The mistakes How to check as you go If you do cut through Common questions

What "burning" means

Burning means going through the gelcoat, usually from too much heat and abrasion in one spot. Once it is through, it cannot be polished back. It has to be repaired.

The mistakes

1. Treating gelcoat as if it is thick. BoatUS notes you should stop if the gelcoat starts to look transparent. Compounding removes gelcoat every time you do it.
2. Too much pressure, speed, or time in one spot. Friction makes heat, and heat plus abrasion is how you go through. Use light pressure and let the compound do the work. On harder spots you can lean in a little more, but never stay in one spot too long.
3. Going over edges and corners. Edges and raised lines burn easily. Tape them off or work them gently with light passes.
4. Compounding over old wax. BoatUS notes wax can cause the compound to cut unevenly.
5. Jumping straight to the heaviest compound. Practical Sailor notes all rubbing compounds are abrasive and can scratch and damage gelcoat if used wrongly. Start with the least aggressive thing that works.
6. Using the wrong tool on a cleaner job. Gritty household cleaners like Ajax can damage thin gelcoat, according to Practical Sailor.
7. Not protecting afterward. A freshly cut surface is exposed. Seal it, or oxidation returns quickly.

How to check as you go

• Wipe the section clean and look at the color in good light
• Stop and reassess if the color changes or looks translucent
• Keep a small test spot to compare against
• Between every stage, wipe the area down and check everything, looking for spots that need more attention

If you do cut through

Stop polishing that spot. A cut-through cannot be buffed out. It needs gelcoat repair, and color matching is the hard part. Tell the owner right away, and unless you have real gelcoat repair experience, send it to a gelcoat repair specialist.

Common questions

Is a rotary more likely to burn gelcoat?

Yes. A rotary cuts faster and gives you less room for error. Keep it moving, use light pressure, and practice before you use one on a customer's boat.

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