How to Lay Marine Fiberglass

Marine fiberglass mat, when used with epoxy resin, forms a durable, weather-resistant shell. It is often used to produce boat hulls, decks, transoms, cabins and other structural watercraft parts. Fiberglass holds up well against pounding stresses and flex, and cures to a hard sheen that can be painted and waxed to a very smooth shine. Laying marine fiberglass on any part of a boat requires some serious preparation to ensure the bond remains leak-proof and sturdy. Properly installed fiberglass can last for years, and is easy to maintain and clean. Any boat owner who wishes to lay marine fiberglass should take his time and follow the application process.

Instructions

1

Place masking tape around the perimeter of the area you wish to fiberglass. If you are working with complete hull sections, use the masking tape to section off areas that will not receive fiberglass or epoxy resin, such as boat rails, cleats and fittings. Mix a solution of hull cleaner in a bucket of water, per the instructions, and clean the area with a brush, removing all wax, algae, oils and oxidation. Dry the area with rags.

2

Connect an 80 or 120-grit sanding disc to an orbital sander and run the sander over the surface, using circular motions. If the area is wood, sand down into the surface evenly, without too much pressure. If the surface is fiberglass, sand down far enough to remove the top layer of the old resin, but not deep enough to disturb the mat fiber. Blow the area clean of all sanding dust with compressed air, and then wipe it down with denatured alcohol and a rag.

3

Mix a batch of epoxy resin and hardener in a container with a mixing stick, providing enough resin mixture to cover the the area with at least two coats. The mixing ratio is approximately five parts resin to one part hardener, or according to the instructions of your brand of resin. Use a foam roller to apply an even, thin coat of resin over the area. Use up and down, back and forth strokes with the roller. Remove all air bubbles, but work quickly to get an even coat thickness. This is the seal coat, and you will let it dry and cure for at 24 hours.

4

Lay a section of fiberglass over the area you wish to cover, leaving about 4 inches of overlap on all sides. Cut out the section with scissors and lay the fiberglass section aside. Connect a 400-grit sanding disc to the orbital sander and sand the area very lightly, using circular and crosshatch motions with the sander. Sand up to the edge of your masking tape on all sides.

5

Blow off the sanding dust with compressed air and wipe down the surface with denatured alcohol. Mix another batch of resin and hardener, using the same formula as before. Use a foam roller and lay down an even coat, which is the bond coat, over the area. Stretch the fiberglass mat over the area and press it down with a dry foam roller, starting in the middle and fanning outward. Make sure the mat lays flat, with no wrinkles or bubbles. Mix another batch of epoxy resin, as you did before.

6

Apply a thick, even coat of epoxy resin on top of the fiberglass mat, covering the weave. Use a plastic spreader to squeegee the surface, starting in the middle of the fiberglass section and working outward towards all ends. Lay the glass over any laps, joints or corners, allowing 2 inches of excess. Let it set for five to 10 minutes, then check for air bubbles. Run the spreader over any high or low spots in the fiberglass. Let the resin dry and cure for 24 hours. This is the fill coat.

7

Sand the area very lightly with the orbital sander, using the 400-grit disc. You may wish to use a finer sanding disc, such as an 800 or 1,000-grit texture, depending upon how smooth you want the finish. Blow with compressed air and wipe with denatured alcohol and a rag. Mix your last batch of epoxy resin, which will be for the finish coat.

8

Apply the finish coat resin with a foam roller, adding some height to the dried undercoat. The finish coat should be thick enough to raise the surface height above the fiberglass mat. You may let the coat dry, sand, clean and then apply a second finish coat, if you wish. You do not need to sand the first or second finish coat. Allow the fiberglass to cure for at least 48 hours or more.