What Eric is refering to is the "Amine Blush" that occurs in the final stages of the epoxy curing (at least w/ WEST Epoxy). Also note that research has shown that epoxies bond better to "cured" polyester resins then fresh/new polyester resins do. But there are a few tricks ...

1) Surface prep is KEY ...
2) You can not rush ... curing times are critical.
3) Gelcoat is designed to cure WITH OUT AIR ... so unless you are using it in a mold you need to have the formule w/ parafin(wax) so it will harden
4) If spraying gelcoat w/ an "aircompressor", compressor oil droplets can cause the gellcoat to never harden. You must use air filters to eliminate the aerosolized (small droplets) oil. Or you can just brush the gelcoat w/parafin on and sand the heck out of it w/ wet/dry paper ... start w/180 grit to cut the wax off then 220, 320, 400, 600, 800, 1000, 1200, 1500, 2000, ... now polish w/ polishing compound and it will look like Jake's!!!

Now, you can accelerate the epoxy's curing w/ heat and UV light. The trick to "amine blush" to let it run it's course which take 3-4 days in a garage/inside .... if outside w/ strong sunlight/UV radiation that time can be reduced. Sand the cured epoxy up to 600 to make sure the repair is Ok ... then resand the repair w/ 220 wet/dry to rough up the epoxy repair so that the gelcoat will adhere to the epoxy.

It's been my observation that most people "rush" the curing times .... with predictable results.

First you need to determine how much is missing from the bottom of your daggerboard, as there are several option on how to do that repair ... 1/2" or 1" or 6" it will make a difference on the technic used.

Harry Murphey