Put on a pair of rubber gloves and pour the amount of fiberglass resin that you need in a small bucket.
Add one- to two-percent catalyst to the resin and thoroughly mix it in, using a stir stick. When the resin becomes one consistent color the catalyst is completely mixed in.
Apply the resin to the site, using a four-inch felt roller. Let the fiberglass harden for 45 minutes to an hour, or until it is hard and cool to the touch.
Put on a respirator and begin sanding the fiberglass. Sand it with 320-grit sandpaper if the fiberglass is getting gel coat. Otherwise you can use 100-grit.