Blisters questions, polyester fiberglass hull, coverd entirely, 1977 Downeaster 38

[Blisterlover]

Hello, I have a 1977 Downeaster 38 sailboat. It had been sitting in brackish water inside the Ballard locks for a long time and the bottom paint was very worn down with a lot of growth. I don't know exactly how long it was sitting there sadly, or if the blisters were there even before this or not. Basically there are blisters in the boat hull, slightly into the fiberglass CSM layer, and they are popping out a little bit. These tiny blisters are about the diameter of a pink pencil eraser, and cover the bottom entirely, spread about 1 inch or slightly less apart on average. In the picture I will attach you can see how they went through the gelcoat/barriercoat (the layer outside of the polyester resin before the bottom paint that I'm assuming has been there since production) whatever it's called, and into the actual polyester fiberglass, only into the CSM layer.

I sanded all the way to the bottom of one, which is in the center of the area on the picture. There was no liquid or water in any of the blisters. There is a small chance that there could have been water so I would also like to consider that, but most likely if there was no liquid inside of these "blisters", not water or anything else. Also further evidence to me that there was no liquid, or slightly more so, no chemicals, at least that would have left a residue, is that there was no seepage from the blisters apparent, no residue left from any seepage, that is, after definitely being dry at this time and being out of the water for 6+ months. So for most intense and purposes I'm looking for information on what would be the cause and outlooks of this situation if there was no liquid at all, but I would also be interested if there could be a difference in the nature of the situation if there had been water inside of these "blisters."

I have not used a moisture meter and tested by sanding down layers, to test layer by layer, to see how far the hull was "saturated." Basically I'm wondering is there any opinion as to the nature of these blisters?

Were they caused by barnacles? One person suggested this to me and I found article on the internet where someone attested that they saw a scientific study proving that barnacles pierce into to gelcoat eventually once they mature past a certain stage of their life sequence. This was supposedly a study done by scientists to help prevent barnacle damage to commercial vessels, so I believe it could be a possibility even though it's not mentioned on any forms I could personally find online when people ask about barnacle damage

If there's no liquid, does that mean that there is no developed acidity in the polyester? Does that mean there is no hydrolysis? Also, does hydrolysis happen on every single fiberglass boat a tiny bit anyways? Is it ever necessary to helpful to remove fiberglass "effected" by hydrlysis if it goes slightly deeper than the blisters?

Also, I'm assuming that these blisters came later in the boat's life and they were due to neglect if not barnacles. How does that make these blisters different than ones that may have happened because of inadequate materials or production methods? Will the repair last longer and will there be less acidity?

I'm thinking maybe take chemical stripper to remove the bottom paint, then take a drill and drill out every single tiny blister, then take a dremel and bevel out the tops of the holes and scuff up the inside a bit. Then take vinyl ester resin and fill the holes, plus about 6 coats with a roller on top of the previous gelcoat/barrier coat thingy that was there I'm assuming since production. Then add bottom paint. Then I would just check it regularly and see what happened.

It would be amazing if anyone has information into the nature of these blisters, recommended repair or course of action, how long they think any sort of repair would last, anything like that basically. Anything we could be helpful or informational. Thank you for reading and thank you in advance for any input or help!

[Benz]

If the boat has been drying on the hard for 6 months, any moisture inside the blisters will have dried out. Likeliest thing is that they're garden-variety osmotic blisters, and simply need to be ground out and filled with the filler of your choice. If you choose to do an epoxy barrier coat (note that the original gelcoat is NOT a barrier coat as they exist today--its purpose is different), then use an epoxy paste to fill--Awl-fair, or Total Boat's substitute. If you want to re-gelcoat (for which there's no reason), use a polyester-based filler--there are several, starting with Bondo and moving up in quality.

[tkeithlu]

Welcome to the forum, Blisterlover.

Nothing there to say that they are any different from the ordinary. So, sand them out, leave the surface a bit rough for good adhesion, use acetone, again for good adhesion, fill and paint, and be glad that Ben gave you some good news.