How to Repair a Hole in a Plastic Boat
Plastic boats like kayaks and canoes are made of plastics such as polyethylene and polypropylene and they are very durable. However, when they are damaged the plastics used by manufacturers are very difficult to bond. You can thoroughly repair a hole in a boat made of plastic with a lot of effort, but your repairs most likely will be obvious.
Force the damaged portion of the hull back to where it was before the accident. This is critical to the repair of a plastic boat
Use a clean paper towel and solvent to get rid of the wax, oil and other grime that would keep the patch from bonding properly. Don't just clean the hole in the plastic but a wider area because the patch will be larger.
Sand an area that's larger than the hole in each direction to rough up the plastic to overcome the lack of porosity of the plastic and you will improve the bond. Use some elbow-grease as you scratch the plastic and be sure that you eliminate the shine from the area.
Use a blow torch a few inches away and only let the exhaust gases reach the plastic. Keep the blow torch moving in an overlapping motion to oxidize the surface of the plastic as well as improve the bond. Try to patch the plastic within about 30 minutes for the tightest bond.
Cut the patches from the fiberglass. Cut four pieces of 2 oz. fiberglass, beginning with one that is about six inches larger than the hole. The other three patches should be increasingly smaller than the first but larger than the hole.
Epoxy the interior surface where the first patch will go. Place the largest piece of fiberglass patch over the epoxy and cover it with a coat of the glue. Apply the remaining three pieces onto the inside of the hull, making sure that each piece is on a new coat of the epoxy. Let the epoxy thoroughly dry before you begin work on the underside of the boat.
Cut one patch about six inches larger than the hole and another that is smaller. Apply a coat of epoxy in the same dimensions and place the larger patch over it. Apply another coat of epoxy and place the second piece of fiberglass on it. It's best to stagger applying the patches on both the interior and exterior of you boat, which will make the patches bend when the boat is stressed.
Sand the patches on both the exterior and interior of the boat after the epoxy has dried. Then paint the area after you have prepared it according to the manufacturer's instructions on the paint brand you are using.