While a hole in your fiberglass canoe or sailboat can look pretty bad, it's often pretty easy to fix yourself, assuming there's no structural damage. With a little bit of patience and some elbow grease, you can get the hull patched up and looking as good as new.
Tools and Materials
You'll need a few things before you get started; luckily, most of these you probably already have on hand or can purchase at a reasonable price.
Step 1: Enlarge the Hole
Enlarging the hole give s a solid base for your patch. Using your sander and medium-grit sanding disc, grind down the edges of the hole to firm fiberglass. Once the sound fiberglass has been exposed all around the hole, taper out to the sound hole so that the outside edge of the hole is 2-3 inches wider than the inside. Wipe off any dust with a soft cloth and clean with acetone. (Caution: take the proper precautions for using acetone).
Step 2: Contour the Patch
Cut a backing piece from the cardboard, at least 2 inches larger than the hole. Cover it with plastic wrap and tape the edges of the wrap down (this prevents the patch from sticking). Set it inside the and check that it the hole completely. Gently bend the cardboard to match the curve of the hull and tape it firmly in place with masking tape. Be sure the curve matches precisely or your patch will be weak.
Step 3: Prepare the Patching Material
Cut your first layer of roving at the smallest point, ensuring it fits the inside diameter of the hole. Successive layers will be cut slightly larger, overlapping the inside layers and feathering out over the tapered edges of the hole. Stack the layers as you cut so you can see when you have enough; once the layers are just level with the hull surface, cut the fiberglass cloth and complete the patch, being sure to overlap onto the sound hull surface.
Step 4: Set the Patches
Lay out the pieces of fiberglass and roving, in order, on a clear surface. Prepare the hardener and polyester resin according to the directions. Starting with the first (smallest) piece of roving, quickly apply the resin with a small paintbrush; it should end up completely wet, but not be dripping. Set it into the hole, centering it in the bottom of the depression; press into place and smooth with the brush, dabbing from the center out to the edge. Repeat with each successive layer of roving, ensuring the edges of the hole are tapered to match the contour of your hull.
Step 4: Close the Patch
Once all the roving is applied, prepare the fiberglass cloth. Set it over the patch and work it down into the resin-soaked roving with your paintbrush. If you need to, a small amount of additional resin can be added, but use it sparingly; too much will make for a weak patch. Let it dry for 8 hours, or for the length of time specified by the resin manufacturer.
Step 5: Smooth the Patch
Once dry, remove the cardboard backing and ensure the patch perfectly matches the contour of the hull. Use the sander to remove any irregularities, then smooth the sanded surface by hand with a sanding block and fine-grit wet-or-dry sandpaper. Clean the area with acetone.
Step 6: Add the Gel Coat
Mix the gel coat as directed and apply a thin layer to the patch. Cover the patch evenly, then quickly cover with a large piece of plastic wrap, smoothing out any wrinkles or bubbles. Let it dry at least 8 hours, or as directed by the manufacturer. Once dry, remove the plastic wrap and sand by hand with the fine-grit sandpaper to remove any excess coating and contour the patch.
Step 7: Finishing Touches
Clean the patch area with a wet cloth and polish with fiberglass rubbing compound and buff. After you've finished buffing the patch, add car wax. That's it! Your hole has been patched in seven easy steps. Contact a company like Idaho Water Sports for more information.