How to Repair a Fiberglass Boat Deck

a red boat on the water
  • 2-8 hours
  • 50-250

Knowing how to repair a fiberglass boat deck is probably one of the more essential skills a boat owner needs to learn. This simple repair job will save boat owners lots of time, will keep the boat in the water longer and out of the repair shop, and is very inexpensive when done with the right tools and materials. Additionally, when fiberglass repairs are done correctly they not only prolong the life of a boat, but increase its resale value.

Simple Materials Needed

Fiberglass cloth material

Gel coating

Fiberglass resin

Bondo brand filler

Molded support pieces


Various grits of sandpaper (80 to 400 grit will suffice for most repairs)

Wire Brush

Electric hand sander

Cleaning solvents

Respirator mask

Heavy duty plastic gloves

Eye protection

Step 1 - Preparation Is Essential

Begin by carefully and diligently cleaning the repair area thoroughly and any surrounding area. Be sure to cut out all damaged sections and edges, leaving clean areas and edges on which to work. Sand the area with 80 grit sandpaper and clean with epoxy or acetone cleaner. Be sure to don a face mask and eye protection before attempting to work with chemicals. Also be sure to provide adequate ventilation through the use of a fan and in an airy environment.

Step 2 - Support Area Being Worked

Most all fiberglass repairs will need to be done from the backside or underside of the area being repaired. Provide supporting material in the form of 1/8 inch plywood which can be tacked on, or taped to the outside of the repair area.

Step 3 - Rough-up Repair Surface

When area to be repaired is thoroughly dry from cleaning solvents and well supported by backing material begin roughing up the surrounding area of the repair site. Do this with a stiff wire brush. Fiberglass needs a rough surface with which to adhere and a wire brush or scraper will provide the right surface.

Step 4 - Begin Repair

Cut sufficient fiberglass cloth material to provide an overlap of approximately two inches. With the plywood backing attached to the other side of the repair apply a thin application of Bondo to fill the damaged area. For best results apply the Bondo filler in thin applications, carefully building up the cavity of the damaged area. Sand the final filler coat of Bondo and apply the fiberglass cloth material. Cover the fiberglass material with one or two coats of fiberglass resin as needed, and sand the final coat smoothly.

To repair the exposed side, stretch the fiberglass cloth material over the repair site, apply a thin coat of fiberglass resin and allow to dry. Work the fiberglass and cloth material to remove any bubbles to ensure as smooth a surface as possible. Repeat applications of fiberglass and resin as necessary to build the surface of the cavity or repair to match the existing surface.

Step 5 - Final Finishing

Once the repairs are accomplished, begin the procedure for adding a final finish. Keep in mind, the smoother the sanding, the better the finish. Start by sanding the final surface beginning with the 100 grit, working up to the 220 finer grit, and ending with the 400 grit for a smoother finish.