Step One
Gather your tools. Once you begin, you'll need to work quickly. Make sure your brushes, scissors, squeegee, epoxy and fiberglass sheets are ready.
Step Two
Cut your cloth. You need at least two layers of cloth. Measure out enough cloth for the area you will be covering. Make the second layer just a bit bigger than the first piece.
Step Three
Remove any damaged fiberglass. Sand the area you will be working on with 60 grit paper and make sure all the debris is blown away. You want the area to be as clean and smooth as possible.
Step Four
Put on some gloves, preferably cheap ones that you won't mind throwing away.
Step Five
Mix your epoxy. You'll probably be using a polyester-based resin. Get some stainless steel measuring cups (or something else that won't melt) and make a mix of 1 to 2 percent resin to MEKP hardener. For example, mix 1 cup resin to 1/2 tsp of MEKP.
Step Six
Lay down your cloth on the site. If you are using different weights of cloth, place the heavier cloth down first.
Step Seven
Apply epoxy. Use the tip of a paintbrush and dab gently on the cloth until it becomes nearly transparent. You can also use a putty spreader to work the epoxy in. Saturate the entire cloth.
Step Eight
Lay down your next layer. First, without dipping your brush into the epoxy again, dab at the cloth so it compacts with the first layer. Now apply more epoxy like you did before.
Step Nine
Swipe the site with a spreader or squeegee. This will remove any air bubbles or excess epoxy. Push firmly, but don't dislodge the fiberglass.
Step Ten
Let it sit. The glass and epoxy have to set. This process is called curing. Depending on the temperature and the job, it can take from 30 minutes to an hour.
Step Eleven
Sand site to your desired smoothness before painting.
Taken straight from
here