How To Work With Fiberglass

Over the next month, I’m going to write a series of instructional posts on how to work with fiberglass and do common types of fiberglass restoration on a boat. This first article explains an overview of how to work with fiberglass and do basic repairs. The second article will show you how to use fiberglass resin.

I’ve done a ton of fiberglass repair on the Rock ‘n Row already, and I still have a bit more left to do. I never took any classes on fiberglassing. I just read one book and rest was self taught. I started small, and my initial attempts were sloppy. As I learned to use the different fiberglassing materials though, my work become more controlled, more structurally sound, and more aesthetically pleasing. I’m going to try to pass on the fiberglassing knowledge that I’ve gained over the last couple years through this blog.


In many ways, working with fiberglass is much like painting. Particularly in the amount of preparation needed. I’ve always been a bad painter, but a great taper. If you’ve done much painting, you know you can do some pretty great looking paint jobs as long as you prepare the site with enough newspaper and tape first. Preparation is even more critical when working with fiberglass.

How to Fix Fiberglass

preparing for fiberglass work

The first step in working with fiberglass is to prepare your repair area by cleaning it thoroughly.

When doing a minor fix to fiberglass or restoring a small area of gelcoat on a boat, the first step is to thoroughly clean the area. After wiping and scrubbing, use a degreaser to make sure no oils or dirt remains. Don’t forget a final wipe down with water to remove the degreaser! Degreasers and other cleaners can leave an oily residue that will prevent the fiberglass from adhering properly.

You can see the mess I had to work with in the picture. This was what inspired my article on degreasing an engine compartment. Although this repair was in my bilge, the type of restoration that I’m doing is very common for fiberglass boat decks. If a heavy, pointed object gets dropped on the deck, it will sometimes take off a piece of gelcoat and fiberglass. These are the same steps you’d take to restore the gelcoat on a boat.

preparing fiberglass repair area

The second step to fixing fiberglass is to clearly mark the repair area.

Once the area is properly cleaned, it’s time to mark out the areas to be restored. In my case, I had several screw holes that went down into the fiberglass. Using a black permanent marker, I clearly outlined each hole that needed to be ground out for repair. The fiberglass on my bilge has brown streaks in it, which made it difficult to see some of the holes. It might not be as hard for you to see the area to be restored on your boat.

After marking the areas, you’ll want to grind out fiberglass as well as the gelcoat immediately surrounding it. Don’t worry, I’ll show you how to restore gelcoat on a boat later. Grinding out the fiberglass gives a clean working area. The idea is to smooth out any hard edges while roughing up the existing fiberglass at the cellular level, to allow for a strong mechanical bond.

repair fiberglass and gelcoat on a boat

Grind out the area around the fiberglass to be repaired. Also grind around the gelcoat. I’ll restore the gelcoat after repairing the fiberglass.

You can see the bit I used to grind out the areas. It’s made of carbon steel and worked really good. I don’t know what it’s called because I just grabbed the best grinding tip I could find at my local hardware store. Then I threw away the packaging. Ha ha!

The point is to use whatever is handy and gets the job done.

Once ground out, your preparation work is complete and you’re ready to mix up some fiberglass epoxy. The next article will show how I do this, as well as the material I use.

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