How to Apply a Clear Gel Coat to a Fiberglass Boat

How to Apply a Clear Gel Coat to a Fiberglass Boat

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Constant exposure to wind, water and sun can wear down your boat's protective gelcoat over time and you'll soon find you need to apply a clear gelcoat to your fiberglass boat. Gelcoat doesn't add anything to the strength of the fiberglass, but it does protect the fiberglass from leaking and from weather damage. Gelcoat can also restore or even change the color of the boat's hull.

Items you will need

  • Gelcoat and catalyst

  • Duratec Hi-gloss additive

  • Small bucket

  • Stirring stick

  • Acetone

  • Styrene

  • Brushes

  • Fine sandpaper and fine steel wool

  • Soft cloths

  • Buffer and pads

  • Fine rubbing compound

Applying Gel Coat

Turn the boat upside down if you can so you have a better working angle. Clean with soap and water and wipe with a rag damp with acetone to remove old wax, oil or grease. Wipe the boat again with a rag, damp with styrene. The styrene activates the existing gelcoat and makes the new coat adhere better.

Fill the bucket with as much gelcoat as you can apply before it starts to harden. Since you are clear gelcoating the entire boat, you won't have to add pigments. Add the catalyst in proportions recommended by the manufacturer.

Thin the gelcoat with Duratec Hi-Gloss Additive if you are using a sprayed so that the gelcoat sprays evenly. You'll have to experiment with the thickness for your particular sprayer. If brushing the gelcoat, apply full strength to avoid brush marks that result from a too-thin application.

Complete the first gelcoat then wait four hours before applying another. The first coat will still be tacky. Press on the coat with your finger. It shouldn't leave an impression with your fingernail. Apply a second coat and allow to harden for another four hours minimum. This coat will be tacky, but hard enough to resist leaving a fingernail impression.

Apply a third gelcoat and allow it to harden overnight. The third coat should have no tack at all after four hours. Three coats should do it, but if you need to add another, just follow the same procedure as before.

Sand the entire hull with 1,000-grit sandpaper or fine steel wool to bring the surface to a dull luster. Dry the area. Load a soft folded cloth with fine rubbing compound an swirl it over the entire hull. Use a buffer to buff in circular motions starting with heavy pressure and getting progressively lighter until the surface becomes glassy and no longer shows swirl marks.

Apply several coats of wax over the gelcoat to further protect the surface from scratches, abrasions and weather damage.


  • Don't thin the gelcoat with acetone or other thinners. This can cause the gelcoat to create an alligator-like rippled surface when sprayed on and destroy all your works.
  • The less you thin the gelcoat, the better it will be.
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