This page outlines how to perform a gelcoat repair on a composite kayak (fiberglass, Kevlar or carbon fiber).

If you have a damaged boat, before you start repairing you should ensure you know exactly what material it is made from (click here for details) and you should make sure you have assessed the damage to decide which type of repair to do. (click here for details).

Materials:
Painter's (blue) masking tape
Sharp scraper or a grinder with small head attachment
Range of wet-dry sandpaper from 150 grit to 600 grit
Small, flat piece of wood to wrap sandpaper around
Acetone
Paper towel
Gelcoat coloring agent (if you want to match the color of your boat)
Gelcoat and included catalyst
Disposable paint brush
Plastic wrap or cellophane
Rubbing Compound (e.g., 3M Marine 1-step fiberglass resotorer)
Marine Waxing Product

Step 1: Tape around the damage.
a) Place a border of masking tape around the repair about 2 inches from the damage.
b) This is done to protect the area around the repair.
c) The more expensive blue masking tape (painter's masking tape) is good because it comes off cleanly even after a few days.

Step 2: Widen any very thin cracks and smooth out any sharp edges.
a) Use the sharp scraper or the grinder to widen thin cracks and smooth out the sharp edges.
b) This is done because gelcoat does not flow into thin cracks and does not bond well with sharp surfaces.

Step 3: Sand the area to be repaired.
a) Sand inside cracks or chips. Sand along the length of the damage not across it.
b) This is done to remove any contaminants locked into the surface of the existing gelcoat and to create a smooth area for repair.

Step 4: Clean the area to be repaired with acetone.
a) Soak a paper towel in acetone.
b) Wipe over the area from edge to edge, not in a circular motion. Wiping in a circular motion just moves contaminants around, but wiping edge to edge removes them.
c) This step is done to help remove contaminants that would interfere with the gelcoat bonding.

Step 5: If you want to match the color of your boat, mix the gelcoat to match your boat color. If you don't want to color-match, skip this step.
a) Mix gelcoat coloring agent with the gelcoat (before you have added the catalyst).
b) Remember to work with only the amount of gelcoat you will need for your repair.
c) Add only a very small amount of coloring agent at a time. A little color goes a long way.
d) Wipe some of the colored gelcoat onto the sanded area to test the colour. Old gelcoat fades on the surface so testing near the newly sanded area will give you a more accurate idea of the colour.
e) Wipe off the test gelcoat with acetone.
f) Note: gelcoat remains the same color when it has dried, so you don't need to worry about compensating for a change in color like with paint.

Step 6: Mix the gelcoat with the catalyst as per manufacturer instructions.
a) Don't mix more than you need for the repair since it will dry after about 20 minutes.

Step 7: Apply the gelcoat to the damaged area using the disposable paint brush.
a) Cover the crack or chip completely and leave the repaired surface slightly higher than the surface around it.
b) Don't be afraid to extend the wet gelcoat beyond the repair area a little to the area that is in tact. This will improve the strength of the repair.
c) Don't go overboard with the amount of gelcoat applied, however, since excess will have to be sanded away later.
d) If the scratch is too deep for one layer of gelcoat, apply multiple layers by waiting until each previous layer has dried "tacky" and then applying the new coat.

Step 8: Seal out the air to allow the gelcoat to dry properly.
a) Cover the freshly gelcoated area with the plastic wrap or cellophane. This will peel off later.
b) Press it down firmly, eliminating any air bubbles. If need be, hold the cellophane/plastic wrap in place with tape.

Step 9: Allow the gelcoat to cure (dry) for a few hours. Then peel the plastic off.

Step 10: Sand the area down to the level of the surrounding surface.
a) Use coarse sandpaper (150 grit).
b) Do not sand with fingers. Wrap the sandpaper around the small piece of wood and sand using the flat surface.

Step 11: Smooth out the scratches created by sanding.
a) Use wet/dry sandpaper and move to progressively to finer papers (220 then 400 then 600 grit).
b) Wet the surface as you sand.
c) Sand in a circular motion.
d) Wipe the surface with a paper towel or rag before moving to each finer paper.

Step 12: Buff the repaired surface.
a) Wipe the surface clean with a paper towel.
b) Apply some of the rubbing compound to the supplied cloth and rub thoroughly.
c) Turn the cloth frequently.

Step 13: Remove the tape and finish the area by waxing it with a marine waxing product.


Information from tapplastics.com
For specific link click here