Question about small blisters

[SJ34]

The cause of gelcoat blistering is moisture seeping in over time then by osmosis will attract more water until the building pressure makes blisters. If the hull is dry as Perithead suggested then barrier coat will block new moisture from getting into the laminate and re-inflating the blisters.

[sailjunkie]

Originally Posted by mitiempo

There is an entire industry stripping off gelcoat and repairing the dreaded "osmosis". There are very expensive tools made and sold specifically for this. Fear is good for this as well as many industries.

Jan de Groot, a surveyor with decades of experience going back to the days before fiberglass has never seen gelcoat blisters progress past the mat layer just under the gelcoat and into the structural roving of a hull, nor one damaged in such a way as to be unsafe or unusable.

Good comments, Brian. Jan doesn't really worry about blisters. Our boat has blisters that I knew about when we made our offer. Our surveyor said they weren't a concern unless we wanted to go racing. His advice was to spend our money on boat toys; not blisters.

I may eventually do something about them, but that would only be if we decide to go with a different bottom paint. If I have to scrape the hull for the paint, that would be a good time to "kill 2 birds with 1 stone".

[Frogwatch]

Just paint over them. You actually do more damage trying to repair them. They are not a structural issue and the boat will sail better than you are able to sail her even with the blisters. Do not worry about them. I've been there, done that and regretted trying to fix something that aint broke.

[SJ34]

Frogwatch makes good points. The last blister job I did was on my San Juan 34. It had thousands of pinhead blisters and one soft spot that at first looked to be about the size of a silver dollar. Non of the smaller blisters got into the mat layer and were just below the gelcoat. The soft spot was from a previous repair and I eventually had to grind away an area about the size of a volleyball and about 3 layers deep to get to solid material that could be built back up. The PO repaired a blister and used epoxy to fair the gelcoat but didn't seal around the repair, allowing moisture to migrate into the laminate.

Even though the pox was just cosmetic I would still repair them if I had it to do over again. The boat sails much better in very light air and bottom paint lasts longer with a smooth hull.

[sidney777]

I did not read all of the posts... Hope I don't repeat... I took off 95% of bottom paint--used Dremel Tool to dig out 1/4 to 1/2 inch blisters--Used thick Epoxy mixed with Copper and bottom painted and barrier coated at same time....Let cavities, holes dry 5 days before painting.
To Remove original bottom paint used Drywall Sander(12 in sanding disc) with vacuum rented from home depot. And rented High presssure power wash with high pressure nozzel and reg sander.
------The Copper mixed with epoxy is a Commercial Bottom Paint and is not ablative. It is hard epoxy just like when you repair something.---

[SJ34]

I would not have mixed copper with the epoxy to seal holes in the gelcoat. That could lead to exactly the same problem I described with my hull. As the copper ablates it will leave voids in the patch which will create a direct path of migration for moisture into the laminate. That is also the same reason you should never barrier coat over bottom paint.

[centaursailor]

As already posted here my repair of blisters is 5 years old now and holding up well. Not sure about the copper mixed into the filler but advice I followed( PBO mag article) was against a barrier coat unless serious remedial work was carried out including full Gel coat strip and dry out.
I painted below the waterline with with International Micron and antifouled as usual.
Safe sailing