How to Restore and Repair Gelcoat

After any fiberglass repair to your boat, the final step is to restore or repair the gelcoat. Gelcoat is a two part epoxy, just like the kind used in fiberglass repair, except you do not use fiberglass or filler and the epoxy contains a pigment to give it a specific color.

Why is Gelcoat Important?

The gelcoat is most important when working with polyester resin. Specifically, this covers boat repairs since virtually all boats are built with polyester resin. Polyester resin will absorb water, whereas epoxy resin won’t. However, polyester resin is about half the price of epoxy. That’s why standard practice in the boat building industry is to build boats from polyester resin and then coat it in an epoxy gelcoat.


How to Gelcoat Fiberglass

prepare gelcoat for repair

A four inch rotary grinder is a great tool for preparing the gelcoat for repair. Be sure to use gloves and a facemask to avoid breathing in the fine gelcoat dust.

In order to get the new gelcoat to stick properly, you need to provide a strong mechanical bond to the surface by cleaning and roughening the surface of the repair area. Cleaning is pretty strait forward – soap and water works great. After that, dry the surface really well. Then, grind the area where you’ll be applying the gelcoat.

Note: It is not necessary to grind away all of the existing gelcoat!

In fact, it’s best if you don’t. All you want to do is roughen up the surface. If you’re trying to repair cracks in the gelcoat, use a pointy grinding bit to grind out the crack. When doing a large surface area like in the restoration shown here, a four inch grinding wheel works really well.

Beware Gelcoat Dust!

repairing gelcoat

Grind the existing gelcoat (and any fiberglass repairs) smooth. Not only does this look better, it provides good mechanical adhesion for the new gelcoat.

When grinding gelcoat, you’ll create an extremely fine powder. This dust is very dangerous to inhale! It’s extremely important to wear a facemask to prevent breathing in this dust. This rule applies whenever doing sanding or grinding on fiberglass, polyester, or epoxy. Although it’s not toxic, this material can not be broken down by your body or passed out of your lungs. As far as I know, this dust will stay in your lungs for the rest of your life.

If possible, I try to have a shop-vac type vacuum with a long extension hose running near me when grinding. It will suck some of the dust in the air away from me. I will also pause frequently to suck up the dust around me as it accumulates. An extension tube can be created by using inexpensive bilge hose from your local chandlery, like West Marine, or hardware store.

Restoring the Gelcoat

how to repair gelcoat

After preparing the surface of the existing gelcoat, simply paint on the new gelcoat.

Once all the prep work is done, applying the gelcoat is easy. Simply paint it onto the area like you would a thick paint. I like to use disposable brushes because I have no idea how to clean gelcoat out of a brush.

Remember that gelcoat is a two part epoxy. That means once you mix it, there is no going back. I’ve heard of more than one person mixing up an entire can of gelcoat to only use a little bit. Given how expensive it is, that’s a huge waste!

Once the gelcoat has a chance to harden, you can sand it down with finer and finer grits of sandpaper. However, if you’re not worried about the aesthetics of the repair job, it’s fine to leave it without any sanding. That’s normally what I do, since polished gelcoat is very slick and I prefer a textured, non-skid surface.

Gelcoat Repair Advise Wanted

Do you have experience restoring or repairing gelcoat? Need clarification on something noted in this post? Please leave a tip in the comments!

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