How to Fill Small Holes in a Fiberglass Boat With Gelcoat

by Kevin Mclain

Gelcoat is used to create a glossy finish to the fiberglass surface of a boat hull. Gelcoat is made up of a resin and a hardener that require mixing before it can be applied to the fiberglass. The gelcoat can be used for polishing and for filling in small holes. Always clean and sand the fiberglass surface before applying gelcoat. If not, the gelcoat will not properly bond to the fiberglass. Wax the gelcoat surface for a more glossy shine.

Clean the surface of the fiberglass with a mixture of clean water and dishwashing liquid. Use a sponge to wipe down the fiberglass surface around the small holes.

Apply acetone with a clean rag to the fiberglass surface and around the small holes. Once the acetone begins to evaporate, wipe down the fiberglass with a rag until it is clean.

Sand over the fiberglass and the small holes with a coarse sandpaper. Ensure that every small hole is sanded thoroughly. Go over the sanded area with a fin- grit sandpaper until the fiberglass surface and the small holes are smooth. Wipe down the excess sand grit with a clean rag.

Open the lid of the gelcoat container. Secure a mixing attachment to an electric drill. Mix the gelcoat and hardener thoroughly. Fill a gelcoat gun sprayer with the mixture.

Spray a heavy coat of gelcoat over the fiberglass and the small holes. Apply the gelcoat evenly to the fiberglass surface to prevent it from running. Once the gelcoat begins to get tacky, apply another even coat of gelcoat and wait for it to completely dry. The gelcoat will harden once it is dried.

Inspect the area around the small holes. Apply more coats of gelcoat as necessary to cover the small holes. Wait for about an hour for the gelcoat to completely harden and dry. Sand the hardened gelcoat with a fine-grit sandpaper until the entire surface is smooth. Wipe away any excess sand grit with a clean rag.

Apply boat wax to the surface of the gelcoat with a clean rag, using small circular motions with your hand. Once the wax begins to haze over, buff away the wax with a clean rag. Continue waxing over the gelcoat surface until it is shiny and glossy.


  • check The gelcoat, gelcoat gun sprayer, acetone and the boat wax can be purchased from most marine and boat supply stores.


  • close Wear safety glasses when applying acetone and gelcoat.

Items you will need

About the Author

Kevin Mclain has more than 20 years of automotive, home improvement and landscaping experience. He has been writing for various online publications since 2002. Mclain has U.S. Army certification in automotive maintenance and repair, among more than 15 additional certifications related to the automotive field.

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