Commonly, plastic canoes and kayaks are made from polyethylene or polypropylene. These low surface energy plastics are hard to bond to, making repairs difficult because the plastic surface inhibits the ability to spread an epoxy adhesive and wet out the surface.
1. Begin by cleaning the damaged area with mineral spirits to remove wax, oil, or other contaminants. Use 60-80 grit sandpaper to scratch the surface around and a little bit beyond the repair.
2. Flame treat the plastic surface to improve adhesion and remove any remaining contaminants. Flame treating means holding the flame of a propane torch 4-6" above the plastic surface and moving it across the surface, overlapping the previous area slightly. Keep the flame moving so you don't burn or discolor the surface.
4. From lightweight fiberglass (4 oz. is fine), cut patches staggered in size, so the largest patch extends beyond the damaged area, with successive patches cut increasingly smaller in size. Multiple layers are best. For a slight tear, three layers of 4 oz. fiberglass should be enough for the inside of the hull and 2 layers for the outside.
5. Starting on the hull exterior, place the largest patch onto the wet epoxy. Apply more epoxy, as needed to wet out the layer thoroughly. Add the second patch, and wet out completely. Allow repair to cure, then repeat the process on the inside of the hull.
6. Repeat steps 1-5 on the interior of the hull. Allow repair to cure. Sand the cured fiberglass to smooth out the edges.
7. If you want to paint the repair to make it look a little nicer, fair the stepped layers on the interior and exterior of the hull by thickening the epoxy with a fairing filler such as West System 407 Low Density Filler or TotalBoat Glass Microballoons. Sand the cured fairing material until smooth.
8. Apply two sealer coats of liquid epoxy and allow to cure completely.
9. Wet sand to remove any amine blush. Allow the surface to dry completely, then apply primer/paint as directed by the manufacturer.