Gelcoat: Quick Guide to Understanding Uses

Gelcoat is referred to as a one-stop solution for almost all kinds of damages on surfaces such as boats, swimming pools and hot tubs. It is one of the most revolutionary materials to be discovered for repairing cracks because it is easy to apply. Gelcoat is extremely durable, and is in high demand due to the strength it provides to any area where it is applied. Basically, Gelcoat consists of a pigmented polyester resin and acts as both, a paint as well as a protective layer, even though it is much thicker than paint. Further, certain additives can also be combined with Gelcoat to protect the surface from damage through UV rays.


There are two different types of Gelcoat:

  • General Purpose Gelcoat is softer, more flexible, and more prone to scratches than the tooling Gelcoat. It is generally used when the surface on which it is to be applied is subject to little movements; e.g. on boats. Due to its flexibility, it adjusts to the constant activity and does not crack.
  • Less flexible and harder than General Purpose Gelcoat is Tooling Gelcoat. It is used on surfaces that are not subject to movement and on surfaces where movement is not desired. Some examples are countertops and bathtubs, where it is preferred over the softer version for its ability to hold the surface together.


Gelcoat uses MEKP as a catalyst, with the latter being added at 1-2% of the total volume of the Gelcoat. Any variation affects the pot-life and cure time of the Gelcoat, as not enough catalyst results in having to wait for a long time to apply the second coat; it also increases the likelihood of contamination. Excessive amounts of MEKP can increase the chances of the Gelcoat shrinkage; it will pull away from the surface.

It is also important for Gelcoat to have a thick consistency; Styrene can be added to decrease its viscosity. Even though acetone has also been used as a thinner for quite some time, it increases the chances of the Gelcoat being rubbery or soft, unlike Styrene, which aids in the cross linking of the resin and catalyst. However, Styrene must not be added in a quantity more than 10% of the total volume.

Method of Application

Due to its viscosity, Gelcoat, particularly the tooling version, is usually sprayed using a Gelcoat gun, which can be procured at marine supply stores. It can also be applied through brushing, but the quality of the final finish is not as good as the spraying procedure. Brushing generally results in a more brittle product as the styrene does not evaporate as easily as it would if a spray gun had been used. However, if there is no other option, be sure to use long and even strokes, unlike when you apply paint. The brush should be unpainted with a natural bristle and wood handle.

Gelcoat is a great product that has been used by many to repair small cracks on multiple surfaces effectively. Proper application of Gelcoat eliminates the need to call a specialist and increases the product’s life significantly.