Did I grind out this blister enough?

[mtcaddis]

Hi, I am repairing blisters on my 1982 Catalina 30. They're are many small ones that seem to not go past the gelcoat so I'm just sanding till they're flat. The larger ones I have ground down to fresh hull. The deteriorated area very conveniently seems to be dyed a blue color so I ground until the blue was gone. There are still some blue fibers left and I don't know if I should keep grinding because those might regrow bigger later. I have pics of the same blister at different depths of grinding. Did I grind far enough?

[a64pilot]

I don’t think so, but I’m no expert. I believe you have to go down to clean glass that has no evidence of a blister having ever been there.
Threat this more as a bump to the top so that an expert can weigh in.

[mtcaddis]

Thank you.

Does anyone else have any idea?

Also when I fill with epoxy, how deep would it have to be before I consider adding fiberglass fabric for reinforcement? And can I epoxy over the gelcoat or should I flare it out wide enough so the epoxy is only over the fiberglass hull?

[mikeyboards]

Whatever you remove has to be replaced .

[a64pilot]

I’m hoping Minaret will show up.
However maybe try doing a Google search here on the forum on blister repair. I’m on an IPad or I would and give you the link.

That last blister looks deeper than just the gelcoat, otherwise I think that I would be tempted to leave well enough alone. It took 35 years to get blisters in the gelcoat, how many more years until they are significant?

When I bought my boat about four years ago, in the survey it had many small blisters just in the gelcoat, like you said. The PO had it barrier coated. My theory is that they pulled the boat on day one, cleaned and sanded on day two, barrier coated on day three and didn’t let the hull dry and sealed in moisture.
Last I saw the bottom was last spring, almost all of the tiny pox had disappeared. My assumption is the moisture trapped by the barrier cost has found its way out, maybe through the inside?

[flyingfin]

Hard to say, put a quarter or your thumb next to the blister when you take the next photo. I see too many people in boatyards grinding out small blisters that will never cause problems. Remember, the fish dont care how perfect your bottom is!