RE: Hull Repair Help
If that repair was done from the outside and you sand it flush, the resin and fiberglass will no longer have anything to hold onto and likely punch thru the bottom.
You are best to start fresh. Grind the area out removing the old repair and feather abou 1/2" all around the hole. If the breach is all the way throught the hull, grind around the hole from the inside as well. Start filling the hole first with a piece of fiberglass and West System or similar epoxy. You will use two layers of fiberglass, the first being smaller than the ground area and the second being the same size as the ground area. If the breach was clear through the hull, put an additional layer inside the hull. Don't use alot of epoxy here, it will float the fiberglass, just use enough to get the glass wet. After it kicks, sand the repair level with the hull, if there are any areas that are low, fill them with epoxie mixed with micro ballons (to a paste) then sand after it kicks. You don't need to sand it to perfection, just give it to your painter, he will do the final finishing before he paints it.