What is the difference between gelcoat and fiberglass resin?

To begin this post, the most important thing is to clarify what is a Gel coat and a Top coat and how they differ.

We can find on the internet these products named as Gelcoat and Topcoat and also Gel Coat or Top Coat, in this post we are going to use both. In the industry, it is accepted in one way or another.

What is a Gelcoat or a Topcoat?

The Gelcoat and Topcoat are formulated through a polyester resin, Vinylester resin, or a modified resin to which later different products are added in the form of additives, dispersants, levelers, deaerators, ultraviolet filters, and pigments that give them the final properties.

Like plastic paints or enamels, the number of colors that you can find in the market is almost infinite, from the colors of the Ral chart to those of a Pantone chart.

White Gelcoat is the most demanded color.

Types of gel coats and topcoats

  • Industrial Gelcoat: the most basic quality on the market. Based on Orthophthalic polyester resin.
  • Orthophthalic Gelcoat: similar to the industrial one. Its percentage of fillers is lower, which significantly improves the Industrial Gelcoat. Named and known as polyester gel coat.
  • Ortho/Iso Gelcoat: although it is not very widespread in the market, it is common for manufacturers to mix both natures to have mixed performance.
  • Isophthalic Gelcoat: the most widespread quality on the market. Based on isophthalic resin. Be careful; we can also find them very loaded.
  • NPG Isophthalic Gelcoat: the king of gel coats in terms of overall performance. Very high quality. Its great resistance to weathering is the highest in the market.
  • Vinylester Gelcoat: the recommended nature for manufacturing rigid molds in Composites based on Vinylester resin.

So when should Gelcoat and when should top coat be applied?

Generally speaking, gel coats should be used when parts are to be manufactured in molds. That is when you want to create a shape from an already molded surface.

In the case of laminates, the gelcoat layer should be used as a base for subsequent coating.

On the other hand, when the mold or part has already been manufactured, topcoat should be used. By including kerosene, the surface will be sealed and without stickiness, which will allow later sanding and polishing to give it a shine (if that finish is really desired). Another effect sought when applying top coat is to repair the flaws of the manufactured piece that may have suffered during the demolding or due to mold defects.

Here is a video where you can see how a skateboard mold is reproduced by applying gelcoat together with fiberglass.

Some considerations when applying gelcoat

The gelcoat must be mixed with meck peroxide for proper catalyzation.

If it is desired to modify the viscosity/blockiness of the finishing polyester paint or top coat, we recommend thinning with Methyl Ethyl Ketone (or butanone) at 5-10%.

To obtain a top coat, you can buy a gelcoat already waxed or add waxed styrene to the gelcoat to convert it into a finishing paint. Both options are available at Nazza.

The gel coat without kerosene is only used as a primer for painting or weather protection, so the finish itself is not so important in this regard. For this reason, at Nazza, we only incorporate gelcoat in white color in order not to influence the color of the subsequent topcoat finish coats, which are available in various colors (blue, black, and white).

When repairing or decorating laminates, the gelcoat layer is not applied to the mold but to the laminate. In these cases, paraffinized topcoat must also be used to allow the resin to cure properly and not become sticky.

Boat paints, topcoats, polyester resins… and much more!

At Nazza, we have a wide variety of products based on polyester resin, as well as a special category of products for nautical use. Here you can find everything from polyester resins to gelcoats, vinyl ester resins, or fillers. Discover it!