Gelcoating vs Painting Your Watercraft

We have seen many misinformed opinions in many Internet forums about the use of Gelcoat as a paintable topcoat. This article is intended to provide that facts and then let you decide which one you will choose. So lets start with a little background about Gelcoat.

Gelcoat is a cosmetic layer of Polyester Resin, thickening agents and colour pigments. It's sole purpose is to provide a quick, smooth, high gloss finish to production molded watercraft and other production parts. It has a consistency like gravy and contains NO self leveling additives. Gelcoat is intended to be applied as the first layer of a female mold. It is applied to the mold using specialty spray equipment to a thickness of 0.5 to 0.8 mm. The Gelcoat layer is applied to the inside of the mold once the Mold surface has been treated with a release agent. After the Gelcoat layer has cured to a tack, layers of fiberglass fabric embedded in polyester resin are applied over the Gelcoat until the desired thickness of the manufactured part has been achieved. Once the layup has fully cured, the part is demolded reveling a Gelcoat finish that is the exact reflection of the surface of the mold.

Gelcoat is not designed to be applied as a painted topcoat

So now lets talk about what can go wrong when mixing and applying Gelcoat.

1. You apply the Gelcoat too thin - Blotchy appearance when cured
2. You apply the Gelcoat too thick - Risk Spider Cracks once the part is in use
3. You under catalyzed the mixture - Gelcoat does not cure
4. You over catalyst the mixture - Gelcoat "Kicks Off" before you can apply it (30-45 minutes)
5. You don't apply three 10 mil coats - see #1 & 2

Now lets assume that you have not experienced any of these issues and you have successfully applied 3 coats to achieve an overall thickness of 30 mils. No matter how carefully you applied the Gelcoat by brush and roller, you will need to do a lot of sanding to achieve a uniform gloss and appearance with the original Gelcoat. For the finest finish, you'll want to wet sand through 1,000 grit before compounding. Make sure that each grit has removed the scratches from the previous grit. Don't move to the next grit without thoroughly rinsing. A wet surface won't allow you to see fine sanding marks, so dry the surface and inspect it before moving to the next grit... Once you've reached the end of your sanding, the 1,000 grit will have brought your surface up to a dull luster. A course rubbing compound shouldn't be necessary and you may be able move to a fine compound like 3M Finesse-it. Follow the Finesse-it with an automotive finish sealant such as Meguire's Machine Glaze. This is followed with a swirl remover such as 3M Perfect-it & a foam pad.

OK so that is the Gelcoat Process and here is the Painting process. Use a good quality marine polyurethane such as Interlux Brightside which has excellent application characteristics and yields that “sprayed on” look when brush applied in thin coats and is ideal for use anywhere above the true waterline on a craft that is continually immersed. Polyurethanes are easy to clean, resists staining and have great abrasion resistance. A hard, high gloss one part polyurethane finish is easy to apply and provides the best appearance with the least amount of effort. Please note that the "above the waterline" disclaimer refers to boats that spend most of their time in the water, trailered boats can use this product on the hull. It is an ideal coating for Canoes & Kayaks. If the boat lives in the water then an antifouling coating would be appropriate.

Some additional facts about using Gelcoat as a paint are that it will add weight to your craft, more weight than paint and Gelcoat is NOT impervious to water absorption.

In closing I should point out that using gelcoat to repair minor dents and scratches is not as arduous as described above, however matching the original gelcoat colour can be a challenge due to aging of the original surface.