TechSheet 53 LAMINATE REPAIR
Construction and repair techniques of fiberglass, Kevlar and carbon canoe hulls are similar. These suggestions cover damage where the laminate is stressed or broken.
FRACTURES If the hull has been severely deflected the inter-laminar bonds may be broken. This shows as a white line or fracture, and the damaged area will be more flexible than the surrounding hull. Repairs should be made to the hulls inside. Sand the interior of the hull around the fractured area with 80 grit sandpaper to roughen the surface. Clean with acetone and a clean rag
Two overlapping patches will be needed. For simple fractures fiberglass patches cut easily, wet out well and sand out easily. Carbon cuts and sands as well but one cannot see voids under it. Kevlar must be cut on a board with a razor knife and the edges must be peel plied as they will fuzz if sanded. Cut the first patch to extend 1” from the fracture, the second to extend 2” from the break. Feather the edges of each patch by removing 1‑2 strands of yarn. Set patches aside in order. Covering the second patch with peel ply eliminates the need to sand.
RESINS Pb Hulls are constructed with Epoxy Vinyl ester resins and cannot be repaired with iso-polyester or normal vinyl ester resins. Vinyl Ester Resins are harsh chemical compounds. Always use a respirator with activated carbon chemical cartridges for chemical vapors as resin vapors can cause respiratory tract and eye irritation. Contact with skin can cause dermatitis and burns; always wear rubber gloves and an impervious apron. Always use safety glasses. Be careful, these chemicals are dangerous.
Methyl Ethyl Ketone Peroxide, MEKP, the catalyst used to activate resins, is a strong irritant. It is corrosive to eyes and may cause blindness. It is harmful or fatal if swallowed. BE CAREFUL.
If eye contact occurs with resin or MEKP, flush with water or eyewash for fifteen minutes and call a physician. Skin contact should be washed off with soap and water. Clothing, brushes and other items may be cleaned with SuperFlush or Acetone. Be Careful with these cleaners.
Epoxy Vinyl Ester resin catalyzes with 2% MEKP; 16cc MEKP per quart of resin, 8cc per pint, 4cc per cup. Most ISO Polyester Resin catalyses near 1% MEKP, 8cc per quart, 2cc per cup. Measure MEKP carefully: too little or too much catalyst will cause incomplete cure. Mix the resin and hardener completely in a throw‑away paper cup or container with a clean stir stick.
Using a throw‑away brush, apply resin to the sanded area. Place the smaller patch in place and saturate it with resin using a dabbing motion. The fabric will take a minute or two to become saturated with resin; fiberglas will become translucent. Continue dabbing with the brush to smooth the cloth and work out air bubbles which appear as white spots. Work the patch until no air bubbles remain. Wet out the second patch in the same manner.
Peel ply is required with Kevlar patches and eliminates the need to sand fiberglas and carbon ones. Cut the peel ply larger than the second patch, apply, then wet out and smooth out air with the resin brush. After cure, remove the peel ply, leaving a mat finish and smooth patch edges.
When finished with resin, place the cup away from flammable objects to exotherm. Considerable heat will be generated, and the resin should be allowed to cool before discarding in a trash receptacle. Similarly, discard gloves, brushes and other contaminated items, or clean with the cleaners listed above, wearing the second pair of rubber gloves and an apron.
HULL TEARS The objective is to rebuild the original structure of the canoe. Butt the torn edges together, using an outer compress to restore hull shape. Ducting tape often suffices, but a cardboard sheet may be required. Place plastic-wrap between the hull and cardboard compress to keep it from bonding to the hull. Clean and debreed the broken interior of the hull with 100 grit sandpaper, removing surface dirt, interior paint, shattered resin and broken laminae. Sand out into solid laminate, forming a dished area, and then roughen the surface of solid hull for 3" around the dish. Brush debris away and clean with acetone. While carbon and fiberglass sand into a shallow dish nicely, Kevlar will not. Remove as much broken Kevlar fabric as possible, using sharp cutters. To remove Kevlar fuzz, wet the edge with water and shave with a double edged razor. Dry thoroughly before continuing the repair.
Cut four patches of successively increasing size to fill the sanded area, with a large, final patch to bridge the break and cover the roughened area around it. Set the patches aside in order, smallest first up. After donning plastic apron, respirator and rubber gloves, mix the resin as described. Using a brush, wet the sanded area, and successively apply, wet out, and work the air bubbles out of each patch.
If Kevlar patches are used, apply a fiberglass overpatch that can be sanded smooth or peel ply. Then clean your equipment and any spills inside the hull with acetone. After the patch cures for a minimum of 8 hours it may be edge sanded. Use porch enamel to match colored interiors.
OUTER REPAIR Fractured or worn areas distorting the canoe's exterior require fiberglass or carbon patches so that they may be sanded to facilitate surface or gel‑coat repair. Minor outer problems may be filled with fiberglass strands, cut about 1/4" long with shears, and resin. Serious damage calls for sanding a dished area in the gel coat to expose sound outer laminae. Sand carefully! Many Kevlar canoes have a thin outer glass layer to facilitate repair.
After cutting glass strands and patches as above, don protective gear and mix resin as above. For repairs on worn through stems, bias cut patched wrap around the shape better than patches cut along the weave lines of the fabric. Fill gaps with a strand/resin mixture, and successively wet out and smooth out the patches, working out all air bubbles. Clean up with acetone, and let the patch cure for 8 hours before sanding and starting Gel-Coat repair.
WARNING ONLY use these materials in areas with adequate ventilation, and keep away from open flame. Protect yourself from breathing vapors and skin contact by using a respirator, plastic apron and rubber gloves. Keep out of reach of children. If you get these materials on your skin or in your eyes, flush immediately with water and call a physician. Acetone cleans tools, but will not remove cured resin from clothing.
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charliewilson77@Gmail.com
Then end result was some new and very pronounced gel coat damage to the canoe. I can't avoid fixing it any longer.
