I''ve done several boats, larger whalers and sail, with nastified hulls that, where repaired, seem to be holding up. Buy yourself a dremel tool and figure out what bits will best serve your purpose. You have gelcoat blisters, as discussed, which may or may not turn into laminate blisters. I believe saltwater blistering is more common, per unit floating, than freshwater. Osmotic migration of molecules is the reason, but osmosis requires a molecular level differential - which saltwater provides, hence, migration. Studies have shown that freshwater standing inside a hull in saltwater MAY, depending on hull quality, more readily cause blistering than any freshwater situation. Use the dremel tool to carefully grind out each and every gelcoat blister. I then take a small grinder and feather the GELCOAT back somewhat. It takes a touch. DON''T flush with acetone, contrary to some beliefs. Blow it clean with high pressure air. Acetone only piles up the waste and causes contamination problems. Once you wipe it with acetone, it''s tough to actually "clean" the surface. Let everything dry. Figure out which West System filler is best for your purposes. There are also considerably less expensive, yet just as good, epoxy
alternatives. Think advertising. Make a peanut butter paste with no more than two squirts of West and hardener and filler, and, using plastic applicators, fill the depressions. When I mix it, if it doesn''t "drip" off the applicator when I hold it up, it''s close to what I want. Don''t mix up too much west, ''cause it''ll kick fast. The smoother the mix the better. Larger amounts of west filler is best spread out on a pallette (plywood or whatever) because it heats up when in thick masses and kicks faster. It will actually combust under certain conditions in a container. Putting it on a pallette will make it last longer and save on waste. Don''t use bondo-level west for the first fill, since you want to basically recreate the hull and gelcoat you''ve removed. Use the softer stuff for final coats. Fill the holes, sand it off, fill again with softer stuff, sand it off and then final fairing and sanding. Between layers of West be SURE to scrub with a scotch bright pad and warm water to "de-blush" the West and let dry before the next application. Also do this before painting. The blush, limiting oxygen to the surface, causes the West to kick off. Better yet, read a west manual before you start. Put a barrier coat on the bottom to mfg specs. and bottom paint
, float. It''s actually pretty easy. You can do a better job than a yard can. Just watch who''s doing it for a living. I''d go easy with the chisel idea. At that point, you might as well pay for a planer to de-gelcoat the bottom. Skip re-gelcoating and apply a barrier coat. Gelcoat is porous no matter what, and won''t provide the protection some of the new barrier coatings.