Q&A for How to Gelcoat Fiberglass

You can apply gel coat with a brush if you are building a fiberglass project in a mold. First you would apply a release agent to the mold, then brush on the gel coat. You can wait 24 hours or continue building your project immediately, the gel coat will not cure until it is sealed in the mold by your fiberglass layers. Third, apply fiber glass layers.

Inspect the boat's finish to see if it is still shiny or has imperfections. If the finish is dull in some places and shiny in others, it is probably time to apply gelcoat.

You can get rid of this stickiness with one more coat of wax. Gel Coat must cure without presence of air; it's often done in a mold so it cures between the object fiberglass and the mold. Two additives will help with a desired final finish. The important one here is wax. Wax in the Gel Coat rises to the surface when it is sprayed, rolled, or brushed, creating a film and barrier that enables the curing to happen. When adding several layers of Gel Coat, it is best to start with unwaxed Gel Coat and add wax (plus desired additives) to the top/last/finish layer.

Gelcoat does not cure in the presence of air. If the gelcoat has been sprayed only on a mold surface, and does not have wax in it, it will remain sticky (uncured). Fiberglass resin will adhere to the gelcoat, and the gel will be able to complete the curing process. Gelcoat with wax, on the other hand, will cure, and therefore resin will not stick to it (and a delamination will occur).

Remove the paint from fiberglass by sanding it off with sandpaper. You can also use a paint scraper, but it doesn't work well on irregular surfaces. Protect yourself with a long-sleeved shirt, pants and shoes. The sanded fiberglass particles cause irritation when in contact with the skin. Protect your airways with a P1 mask for the same reasons. Wear gloves and eye protection.

Polyester filler is made of the same material as polyester resin (AKA fiberglass resin). It will bond and be of similar hardness.

No. Discard the curing gel coat/resin. It will no longer be useful after it starts to harden.

Both cured fiberglass and cured gel coat require sanding before any subsequent application of resin or gel coat. This applies whether or not the resin or gel coat was waxed. Sanding does remove the wax layer, but the main point is that cured resin or gel coat will not accept/bond with new applications unless it is prepared through sanding to form a mechanical bond. Unwaxed resin and unwaxed gel coat do not harden/cure unless air is not present (which is easily achieved by covering the surface with waxed paper or plastic wrap). Laminating resin, i.e. without wax, and gel coat in the open air will not dry but remains tacky and does not require sanding; it will form a strong chemical bond.

Try using Poolcoat or Flocoat. These brands are Gelcoat with wax added. Or, add Waxol to your Gelcoat at a .5% ratio. Anymore than that can change the colour.

Gelcoat needs to be between 400 and 600 microns for both painted panels and for gelcoat-finished panels.

Yes, in fact once the gel coat has been applied, the pattern must be immediately pressed into the gel coat in order for it to cure around the pattern. Non-slip areas such as boat swim platforms and deck floors, have a diamond pattern that can be purchased for use when repairing and gel coating this area.

The short answer is yes, as long as it's smooth. Not every fiberglass surface requires gelcoat (chairs, table's etc). As long as the surface is smooth and non-porous, wax can be applied.

Yes. You can contact gelcoat supply companies like Spectrum, which can mix up your custom color in the quantity you need with hardener and ship it to you.

Use a brush, because it forms a thicker and more equally-spread layer.

Gelcoat is a liquid that hardens to form a thick, protective layer over a fiberglass surface. It's used to provide a quality finish over fiberglass. Gelcoats protect the surface from scratches and moisture damage, while also adding a shiny, smooth finish.

Gelcoat takes 4 hours to dry after you apply it. Even you're adding multiple layers of gelcoat, be sure to allow 4 hours of drying time between each coat. Press into the gelcoat with your fingernail after you've allowed it to dry. If your fingernail doesn't leave an impression, then it's dry.

Yes, you can apply gelcoat over a surface that's already covered with gelcoat. If it's a large surface such as a boat or a bathtub, use a gelcoat spray gun to apply a coat over the existing coat. For smaller surface areas, like a chair, apply the gelcoat using a paintbrush using short, vertical strokes.