I recently had to repair the keel of a mono that was in a hard hit during a race. I used Epoxy to make the repair on the hull. The damage was through the gelcoat and well into the glass. Unfortunately I didn't think of taking pictures before the repair, but it was a standard repair, that we all have to do at some point or another on our boats after a mishap. The boat being black gelcoat, I mixed graphite powder into the West Systmes expoxy to get a nice opaque black resin. No glass was used in the repair as the boat was not broken through, just the keel damaged.
Typical steps were taken to clean out the repair area, remove all loose material, including chipped and cracked gelcoat. I then filled in the damaged area with the resin I had mixed up, but this is where I ran into a problem. When I started applying the resin, I noticed it was running a lot down the sides of the repair area and was going to be a much bigger area to sand and clean out than I wanted. Being the repair was right on the keel it was kinda hard to get away from this. Anyway I put on the first coat, scraping it back up to the top of the keel until it started to gel. I applied the second coat before the first had time to set (to get a chemical bond between the two). This time I was really scratching my head to figure out a way to keep the resine up at the top of the keel so that I would have enough material there to sand it back down to the proper shape and angle.
Here is the answer, and it worked great! I waiting for it to start to gel again and applied some wax paper over the repair. Then I used a plastic scraper and shaped the repair ares to the shape of the keel. This also allowed me to keep the excess resing over the surrounding area to a minimum ( I hate sanding! ). Once cured, the paper peeled right off, and I was left with a repair that required very little sanding. Turned out great! A clear coat and it is ready to go!
Maybe a lot of guys already knew this, or have other/better techniques, but this worked really well for me and just thought I would share.