Originally Posted by misfits
The proper way to do this.
Duct tape & plastic over thru hull hole inside the boat. Grind back the hull on an angle, 4+" around the thru hull. Cut fiberglass mat in circles, each one a little smaller than the next. Start w/ the largest & keep pilling on the smaller patches in sequence. Once you're at the desired thickness, slap the fairing compound on.
Most mat is not compatible with epoxy. Biaxial roving is a good choice as would be heavier fiberglass cloth. As posted by others the epoxy only plug is not a very good method. The proper method is shown below. Note that the largest patch is put on first. This eliminates the chance of sanding through it during finishing weakening the repair.