You have gotten some very good advice here but let me fill in some of the gaps....
Ablatives, like all bottom
paints, over time eventually loose adhesion on the lower most layers. When this happens, ablatives have fewer layers of
paint to remove than other harder forms of
paint. Ablatives are prone to
paint sickness (as are most other
paints) and it shows up as small spider crack, or as peeling
paint. Those areas where peeling or spider cracking is occuring should be sanded down to a base layer that ideally is solidly adhered.
The presence or absense of ablative anti-fouling bottom
paint has no impact on blistering. Typically the gelcoat and when present the barrier coat, are the water resistant membranes that form the defensive
line against osmotic blisters.
It is a good idea with ablatives to sand down through ''last years
paint'' so as to prevent a build up. Too much
paint is far worse than not enough.
Sanding should be done with increasingly finer grades and the strokes should run the direction of the water flow. I typically use 180 grit to prep for the first coat of bottom
paint and 220 for the second coat.
Wearing gloves, I typically wipe down the hull with denatured alcohol, which typically removes any dust and any oils or greases or other contaminants that might compromise adhesion. Frequently change paper towels or clean rags so that you are not simply redistributing the same contaminents.
Masking tape off the waterline and the depthsounder transducer.
Two gallons is a lot of
paint to
paint the bottom of a typical 30 footer. I typically got 2 1/2 coats out of a gallon on my prior boat, a 28 footer. With ablatives, I would typically ''spot in'' (with an extra coat) the bow, waterline, keel (leading edge and bottom) and rudder as these areas experience more erosion than the rest of the hull.
I would typically roll on the bottom
paint with a tight nap roller in a couple square foot area at a time and then ''tip off'' (drag the tip of a brush over the surface of the wet
paint) the surface with a foam brush stroking in the direction of the water flow. Tipping off does several things. It levels the high spots in the rolled on
paint which greatly helps with light air performance, but more importantly it increases adhesion and removes bubbles from the
paint layer. I typically apply several coats of
paint in a weekend and feather edge the
paint maybe 6 or so inches away from the jackstands and then have the yard move the jackstands applying saranwrap to the top of the jackstand to prevent damage to the new
paint and then feather in the
paint at the jackstands.
When the
paint has dried, I typically wetsand with 400 grit in the direction of water flow to knock down highspots in the
paint for performance reasons.
The advise about a high quality dust mask, tyvek suit and goggles is very important. You expect to be around for a while and playing casually with toxic
paints is not worth taking a chance with.
Lastly, here on the Chesapeake most of us stay in the water year round and so only
paint our bottoms every other year. You can typically get a year per coat out of bottom
paint depending on whether you use a diver and how often.
Good luck,
Jeff