Join Date: Feb 2000
Location: Annapolis, Md
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Bottom Job question(s)
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.