Why is gelcoat sticky after applying to fiberglass?

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.