Applying fibreglass over plywood can be a tricky process, whether you are covering a small piece or an entire deck. There are multiple benefits to the process, however. Fibreglass is strong and waterproof, two features that the plywood does not share. All of the materials for this project can be purchased at your local hardware store. If you are planning to cover a large amount of plywood, you should practice with a small piece first to learn the technique.
Sand the entire plywood surface using a palm sander and 80-grit sandpaper. The surface must be roughened for the best adhesion with the fibreglass.
Wipe the plywood with a wet rag to remove any sanding dust. Allow the plywood to dry completely.
Cut two sheets of fibreglass cloth slightly larger than the plywood surface. If you cannot find a piece big enough, you will have to join several pieces as you apply them.
Mix a batch of fibreglass resin with its catalyst in a large bucket. Follow the mixing ratio provided with the resin carefully: if you add too little catalyst the resin may never fully harden, but if you add too much it will harden too quickly to be useful.
Spread a layer of resin onto the plywood with a large brush. For larger projects, use a roller on a pole.
Lay one of the sheets of fibreglass on the surface. If you must use several pieces, line them up next to each other with as little gap between them as possible.
Brush or roll more resin onto the fibreglass, starting in the centre and working your way outward. You want to both saturate the fibreglass with resin and work out any air bubbles.
Apply the second layer of fibreglass. If you are using multiple pieces, align them differently from the way the first layer was laid so that the seams do not line up.
Apply resin to the second layer of fibreglass, then allow the entire project to harden overnight.
Trim off the excess fibreglass from around the plywood edges. Sand the surface of the fibreglass as needed.
Wear protective gloves and clothing when working with fibreglass and resin. Wear goggles and a dust mask when cutting and sanding fibreglass.