I panicked with the thought of using Gelcoat as well. I built a wooden canoe using West Sytem epoxy and learned to clean the amine blush from the cured epoxy with each coat. I was preparing the canoe for varnish and bought the best varnish money could buy for my cool canoe. The varnish never dried!!!!
The only answer I received from the varnish supplier was to strip the varnish, clean the amine blush and revarnish.
I was ready to kill. This must be the same way with gelcoat!
I recommend cleaning the epoxy well to remove any possible trace of the amine blush that will FU your gelcoat job. Maybe even call West System support for their input on best chemical to do so. I know warm water and plastic brillo pad generally takes it off, but I would be sure. Then....
I followed everyone's recommendation and even called Jeremy (thank you!) for support questions prior to starting the project. Here is my to-do list after completing my glassing repairs;
1) Purchase cheap HVLP paint sprayer from Harbor Freight or cheap auto store, approximately $20.
2) Purchase enough Acetone to clean your tools. Gallon or more.
3) Purchase your gelcoat. I used gelcoat from Fiberlay in the Seattle area, mainly because they are local, but it works! I used the gelcoat with the wax mixed in so it cured on its own! I think this is key as well as FRESH batch of gelcoat. Don't purchase from large marine store like Karl B. did and never dried.
4)Sand the whole area smooth first with 18" board air sander with 120 grit to fair the hull.
5) Sand with orbital air sander.
6) Tape area with masking tape and masking paper to cover upside down hull. (I only completed a bottom job)
7) Clean hull with Acetone. Make sure to only wipe one direction and make sure it is clean. I mean more acetone and wipe two to three or more times to make sure. This will be your only chance and you do not want to have any contaminants on the hull.
prepare to spray, meaning have respirator, goggles and gloves.
9) mix no more than a pint of gelcoat and spray. It took me about 2-3 minutes the first time to get the spray pattern right.
10) spray until you are out of gelcoat. In my case it was almost 5 coats of the bottom of the 21SE. I was going on thick also. Do not let dry between coats. I more or less just started spraying and never stopped.
11) clean quickly with Acetone. Make sure your spray gun is clean or throw it away.
12) Remove tape and masking paper and let cure. I let cure 48 hours as I had time.
13) I then used the orbital palm sander with 180 sand paper to smooth tape ridge and knock the high points off. This was easy as I already had a faired hull.
14) I did not sand with finer grit. I used buffing compound and buffer to melt/shine the gelcoat. Other than being brighter white that the original you cannot see the blend line.
I thank my lucky stars when I hear the nightmare stories, but I think being overly anal about the preparation is the key to all fiberglass and painting projects. Follow directinos exactly and you should do fine.