Blister Repair

Crossroads needed new bottom paint and also had hundreds of blisters that we needed to address. We hauled her out at the boatyard of the Napa Marina and had the bottom paint sanded off. Next, we opted to do the blister repairs ourselves. We used Don Casey's book "This Old Boat" and any other information we could learn about blisters. There are a couple of things we learned along the way that didn't show up in any of the books we read or internet sites we found.

First off - once the bottom was sanded, the blisters were not as easily identifiable. They were now flat and so to identify them was a little more difficult. Second - there were probably hundreds of places where the bottom seemed to "seep" moisture but were not necessarily full blown blisters. We consulted professionals at the boat yard and learned that there were so many of these that to properly address them all, we might need to remove the gelcoat and have it reapplied. "This Old Boat" addresses this as well and we concluded that the cost for this was prohibitive. We walked through the boatyard and examined other boats with blisters and found they seemed to have the similar types of "wet spots" that were not being addressed. We decided to grind out the obvious, large blisters and let the boat dry out for 1-2 months.

Identifying the Blisters:

Once sanded, the bottom was smooth and the blisters were not as apparent. To identify them, I looked closely at the color of the bottom and where there seemed to be the dark areas surrounded by a sort of ring, I drove a chisel or paint tool into the center. If it was fairly easy to penetrate the surface, I kept going until moisture came out. Moisure (full of toxic chemicals) often squirted out in all directions and so I was always careful to wear eye protection and gloves. Using this approach, I discovered what the sanded blister looked like and could find them fairly easily.

The areas that seemed moist, but did not show this discoloration, I left alone. I decided to do this because after I attempted to penetrate a few of them, I found they did not squirt or ooze moisture - but that the discoloration seemed to be primarily right on the surface. They could still be "blisters in progress" - but I decided that dealing with each and every one of these could be more destructive and lead us to the option we were trying to avoid - stripping the gelcoat and replacing it.

Grinding out the Blisters:

I attempted to use a chisel or painter's tool to grind out the blisters. This was really hard on my arms and the palm of my hand which I used to apply pressure to the handle of the tool as I was doing the grinding. I calculated that this process would take me about 1-2 weeks. I was not able to work particularly fast because I found my arms and neck getting tired working overhead when I was under the boat. Someone at the boatyard saved my life by loaning me a die grinder. This die grinder attaches to an air compressor and between Ken and I, we were able to finish grinding the blisters in about one day. This tool was worthwhile enough that if I had to purchase one, I would. However, because it was so much easier to grind out the blisters, we had to be very careful not to overdo it by grinding too wide or too deep in each blister.

Washing out the Blisters:

We used TSP mixed with water to wash out the blisters. We also used a rounded brush - the kind for washing hub caps or wheel wells. It is nicely rounded so that we could get inside each cavity to more thoroughly clean it.

Drying out the Blisters:

Crossroads is now in dry storage where she will remain for 1-2 months. Using what we learned from "This Old Boat," we'll test various places on the bottom for moisture periodically -- including those places that appear to be wet, but didn't appear to be full blown blisters. The tough thing is missing all of the sailing we could be doing if we speed up the process. I'll update this blog once we can describe this process and the results.