Join Date: Jul 2006
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Ah, Blisters. I've spent a year repairing this issue... part time (very part time). The most common cause of blistering is thru osmosis. Polyester resin is not 100% waterproof. As water reacts with the chemicals in the resin used in the fiberglass layup, a gas is created, and expands. Viola! A blister of the gelcoat is the result.
More often than not, blisters are a result of a "void" (or air pocket) in the original layup. Although not serious initially, it can become quite serious and result in delamination of the hull. Can you say "Catastrophic Failure"? It must be delt with immediately. A more serious condition is what is commonly called "boat pox". This usually shows just as it sounds; hundreds, maybe even thousands of blisters. This condition will likely show the hull to be saturated also. Now you have a very serious condition. The boat would need to be hauled and probably spend at least a summer out drying out. Additionally, the gelcoat will need to be stripped for the hull to properly dry. Only when the hull is sufficiently dry can repairs take place. It is a huge job and very expensive at a yard.
All that being said, I have done my own "blister repair". It is not difficult, nor complicated. However, it is extremely time consuming. One of the biggest jobs I had was getting 30 yr old bottom paint off. Strippers - nope (worked on the outer layers but would not do much of anything to the last layers). I ended up sanding the entire hull. Arghhh.
Yesterday, I spent the morning (had to sail in the afternoon) sanding down my initial fairing work. I was surprised how easy it was. I used the West System. I was expecting it to be much worse than the old bottom paint. I was wrong. I finished half of one side of the boat in just a couple hours.
One note regarding bottom barrier paint (I'm using Interlux 2000E). Everything I've read indicates that this goes over your repairs (like primer). It is not part of the repair. Additionally, it is paint, not epoxy. Use real epoxy for the repairs.
Hope this helps.