blisters

[fishy]

I would be grateful for any advice after a stressful weekend.
12 monthes ago I bought a ten year old 30 ft GRP boat apparently epoxied from new. I had it surveyed by a reputable surveyor who said it was structurally sound, had moisture levels within acceptable limits and that there was no evidence of blistering on the hull.
When the boat was taken out on Saturday there was clear evidence of blistering. There were two types of blister. The first ones were fairly extensive evenly across one side of the hull. They were small (say 2-3 mil)and uniform in size. When I scraped at them they came off easily and it appeared the gelcoat was unaffected underneath. No water came out of the small voids and there was no strong smell .
In a much smaller and specific square area there were some slightly bigger blisters.On scraping at these some of them were wet and in several places digging deeper it seemed that there were fibres from the laminate which were exposed and wet.There was however no smell. The small place that was affected was on the port quarter. One theory that was suggested by a very helpful local boat builder was that this would have been where the boat might have been shored up when it was out of the water precviously and that the water had got in from constantly damp carpetting etc that might have been next to the hull. In fact the boat did spend a couple years out of the water in the mid nineties and a photo the previous owner showed me did show it shored up in that position.
My questions are; A) Did I ought to worry about the first small blisters and how did I ought to treat them.B)What about the second much smaller area of blisrters where there was evidence of moisture under the epoxy but no smell.C)Do I have any comeback against a surveyor who only 12 monthes ago gave the boat a clean bill of health.
Any advice or ideas would be very gratefully received because I am fairly new to all this .Thankyou .

 

[longjohnsilver]

Don't get too worried, even if they are osmotic blisters (I suspect they probably aren't) it's not the end of the world.

The small blisters cannot be osmosis if they are above the gelcoat, they sound as if some of the antifouling has reacted with some of the older coatings.

The other blisters you say have no smell, if they were osmosis they should have a very distinct vinegary smell, without this smell I am unable to guess what the problem is, however I would scrape them all out, give them all several good washes with fresh water, dry them out and fill with epoxy resin.

To treat the smaller blisters I would suggest just scraping off the old antifoul, or consider having the whole hull slurry blasted back to the gel coat and then re-antifouling.

As regards to the surveyor, why not contact him again and ask his opinion, he will almost certainly want to help. It seems the only area of real concern may be where the boat was shored up in the past and I do not think it reasonable for a surveyor to pick up on this, his moisture readings will have been taken from a certain number of places on the hull, so small areas could easily have been missed. Also you say the moisture is under the epoxy, does this mean it's between the gel coat and the epoxy coating? If so again I would not be too worried about it. As I say speak to him with your concerns.

Hope this helps and let us know how you get on.

 

[oldsaltoz]

G'day Fishy,

The advice provided by Longjohnsilver is good stuff. I would add the following notes.

If the small surface paint blisters are less then 4 inches / 100 mm apart, you will almost certainly have to remove it all.

If the small area of blisters turns out to be into the fibreglass, after you have fresh water pressure washed and dried it. Use only epoxy resins to repair the voids and no chopped strand fibreglass at all, only glass suitable for epoxy should be used,

After filling, you need to apply at least 3 coats of epoxy resin, remember to wash each cured layer with a scourer before a light sanding, it's clean when water no longer forms beads, just use fresh water only.

A couple of coats of International Interprotect or similar will help prevent further problems, apply the first coat of antifouling with the last coat of Interprotect still tacky, this ensures a good key.

I hope this Helps

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