Join Date: Feb 2011
Location: San Francisco Bay area
Thanked 80 Times in 80 Posts
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The first thing to check is the nature of the blisters, by grinding one or two down. Sometimes you get blisters in the paint, caused by poor adhesion at one of the layers - these are not true blisters, and nothing to worry about. Usually caused by the yard applying paint in less-than-ideal conditions (too damp, not enough/too much time between coats, etc).
For 20-30 true blisters, I woudn't be taking all the gel coat off. Grind them down, epoxy, then interprotect the whole bottom, then bottom paint. Will probably have to repeat this every few years.
Bristol 31.1, San Francisco Bay