Gel Coat Scratch repair

Fixing Hull Scratches / Gelcoating


By Bryan Diffendaffer 

As an alternative to removing scratches with sanding, I use gelcoat. Do not try to sand the scratches out. Clean them up so that there is nothing in them and spray gelcoat right over them after you have prepped the area. If you cannot get the scratches clean then you will have to sand them out while blending them into the surrounding area. Gelcoat is a little transparent and any blemishes underneath might show through. If you do have to sand them out it just means you have to put more gelcoat back on. No big deal really.

I have refinished one boat complete and spotted repairs on several others boats in our club with gelcoat. While I do have some experience, I do not consider myself to be an expert. But I will tell you what I know.

Gelcoat is expensive and difficult, but not impossible, to work with. It does not behave like paint at all. It does not flow out after you spray it and needs to be wet sanded and buffed to get it flat and make it shine. It needs to be protected from the air while it cures. I think it is a little soft when compared to paint ,especially the white. The black is a lot harder but who wants a black boat. The white also seems to be a little transparent once its polished up depending on how thick it is.

On the plus side you can spray it on year after year and it creates a homoginous finish unlike paint which forms a definate boundry with the fiberglass or other paint under it.

It sands well unlike paint and because of this I think it is easier to keep your boat looking new year after year without investing a lot of work or adding a lot of weight.

I use a touch-up gun to do spot repairs or an automotive paint gun for larger areas. Use a good gun. The gelcoat goes on best when it is thick (viscous) and a good gun will shoot it better. I've tried using a foam brush on repairs, but it leaves heavy brush marks in the gelcoat and you end up sanding most of it off anyway.

Sand the area to be sprayed with 80 grit with a d/a sander. Thin the gelcoat with styrene monomer until the gun will shoot it reliably. Don't forget the catalyst.

I usually put two coats on, waiting for the first coat to flash off before applying the second. Put it on as heavy as you dare. Just don't run it off on the floor. Don't wait too long before applying the second coat. Gelcoat needs to be protected from the air to cure correctly. I use PVA (poly vinyl alchohol) to seal the gelcoat. There are other agents that can be used. Some you put right in the gelcoat, but I have only used PVA. I spray it on with a cheap gun. It goes on ugly but it works. I usually thin the PVA with a "little" water. It seems to spray and flow a little better. Don't get carried away, a little goes a long way.

Deciding when to apply the PVA is the most important part. Spray it on too soon and the impact will cause dimples in the gelcoat, too late and the gelcoat will be at best slow to cure and at worst may never cure. Try to put it on when the gelcoat starts to firm up but is still soft. Experiment a little. After the gelcoat has cured ( about a day if its warm ) wet sand the repair starting with 220. The PVA is water soluble and washes right off when you sand. Work your way up to 600 wet and then use a buffer and compound. I use 1000, 1500 and a glaze which is about 2000 grit. I like my boat to shine. I think it stays cleaner with the smooth finish. You serious racers stop where ever you want.

Be sure and put something on the floor before you spray. The gelcoat that finds its way to the floor will be very slow to cure. You don't want a sticky garage floor for the next three months.

I hope this helps. If you have any questions feel free to E-mail me. 

Bryan Diffendaffer and his very shiny Nacra 5.8 "Unleaded Only"
Southern Idaho Sailing Association 

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