With hesitation...

There are two kinds of gel coat, for two different purposes, the same as there are two kinds of polyester resin - one includes wax in the formula, and the other doesn't. The waxed product is intended to cure in air when the wax rises to the surface during the cure. The unwaxed product retains an uncured surface which will chemically bond to the next layer in a lamination. Typically, but not always, waxed gelcoat is used as the final layer in a fiberglass hull repair. Typically, but again not always, unwaxed gelcoat is the first layer applied inside a prepared mold prior to adding mat and cloth in a polyester resin/fiberglass layup.

The major advantage of unwaxed polyester gel coat and resin is that when constructing a large layup, for example for a commercial fishboat hull, each applied layer will retain an uncured surface over the entire hull surface until the next layer can be applied. When constructing a large boat, it would otherwise be impossible to apply the layers quickly enough to achieve a a uniform and complete chemical bond between all layers. With polyester resin, this would be a serious structural problem because the mechanical bond with polyester resin is relatively weak.

Waxed gel coat or resin are, in contrast, intended to cure with a hard completely catalyzed surface, and are generally used in repairs of one sort or another. If waxed gelcoat is applied professionally with a spray gun, it goes on very smoothly, and requires relatively little sanding and polishing. This process is a standard technique in fiberglass boat repair.

Waxed gel coat is not paint, the catalyzed nature of the cure is different from the cure mechanisms used by most paints, even the two part ones. In any case, the mechanical nature of the cured product is also different. Cured gelcoat is hard, but has poor tensile strength - i.e. it is brittle. One of the reasons I would not use it to finish a kayak is that if the coating was not kept quite even and thin, there would be a high likelihood of hairline cracking developing in locations with flexing, such as where bulkheads meet the inside of the hull. Most paints retain a greater degree of flexibility and tensile strength, and also have a lesser tendency to be applied too thickly, so this problem would be less likely to occur.

Finally, as mentioned before, and this is important, if the original finish on the kayak was epoxy, polyester gelcoat will not bond well to it, and there would be a risk of peeling or chipping, especially in response to minor scratching or at flex points.

Bottom line is still, in my opinion, use paint, not gel coat to refinish the kayak.

Merry Christmas all,

Allan Edie