1. Clean area with acetone. Sand with 40 grit, feathering out the edges.

2. Hand sand with 80 grit.

3. Wipe with acetone, and then with Styrene, this will create a chemical reaction to the old gelcoat and allow for the old and the new gelcoat to become one instead of only stick.

4. Mix gelcoat putty and apply.

5. The putty should be higher than the surrounding area to allow for sanding.
Let dry for approximately 1 hour.

6. Sand with 80 grit on a sanding block.

7. Spray with gelcoat. Let dry.
Wet sand using 400 grit, 600 grit, then 1000 grit.

Gelcoat putty :
Gelcoat + Pigment + 5% paraffin wax + Filler (Thixotropic Silica, Talc, Glass Microspheres.....)

Gelcoat to spray:
Gelcoat + Pigment + 5% paraffin wax + 10%-15% Styrene Thinner

you can use preval spray gun

http://www.prevalspraygun.com/

before you start It is recomended to test this not on the boat