Re: Blisters on one side

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Posted by B.B. on February 14, 2005 at 09:13:01:

In Reply to: Re: Blisters on one side posted by Guido pas on February 14, 2005 at 09:10:55:

Posted by Bengt Blomberg on November 09, 2004 at 07:03:44:
In Reply to: Re: Blisters on one side posted by Guido Pas on November 08, 2004 at 03:54:33:
Guido, if you sand the gelcoat even all over the under water part and then apply a water based epoxy resin (normally used for painting concrete floors) in two coats before the antifouling there will probably be no problems. This type of epoxy will let out the vapor presure formed in the cavities without blistering. As it gets out slower than it can pass through the antifouling, also that will not blister. Further new algas will hardly be able to pass into the cavities.
The normally most easy to find epoxy of this kind is the SIKA Sikafloor 2530W.
Paint one layer one day, another the next day and the antifouling no later than two days afterwards.
Then let cure for a week before launching
The blisters might be slightly acid but that is harmless acetic acid only.
Regards Bengt

: Thank you Bengt,
: : Now I do not have to be bored during the winter season! I have quickly glanced through your book, which raised some more questions.
: : There are hundreds of small blisters on the affected side, so drilling these wholes is a lot of work. But I can imagine that, if I leave the boat in the same place next year, there will again be hundreds of blisters next year. Or do you think the proces will stop eventually? Or is there a more permanent solution?
: : Will it help to turn the boat every other week, or will that just cause the same problem on the other side? From your book I understand that the temperature is very important. The affected side is on the sunny side, and with a dark green hull, it can get hot!
: : If I just sand them away and apply antifouling, the antifouling will start blistering you say. Is that harmfull or just ugly?
: : Should I test the acid content of the blisters?
: : Regards, Guido

: : Posted by Bengt Blomberg on November 03, 2004 at 12:31:50:
: : In Reply to: Blisters on one side posted by Guido Pas on October 30, 2004 at 08:16:50:
: : Hello again Guido!
: : Most laminates from that time have small cavities
: : in the first lamimnate layers under the gelcoat. During the first 4-5 years these cavities become filled with water mixed with acetic acid from hydrolysis of the coating layer on the fiber glass. This has nothing to do with the dangerous hydrolysis of the polyester itself. You can find a total explanation in my book but it is to long and needs illustrations that I can not provide here.
: : Of some reason the content in those cavities attracts algas which cause the content to expand which results in such small gelcoat blisters. As the quai most probably is covered with algas too, that side of the hull is apt to be affected first.
: : You can sand away the blisters, but then most probably the antifouling will blister instead.
: : Unfortunately the outward opening of the cavities is a pinhole only and does not allow filling them without drilling a 3-5 mm hole into each of the blister bottoms but that provides a lasting solution.
: : Regards Bengt

: :
: : : Posted by Guido Pas on October 30, 2004 at 08:16:50:
: : : Hello Bengt,
: : : Two years ago you gave me some advice for my 30 y old ship (wet spots, no blisters). At that time i performed the acid test by drilling holes. No acid was found. I have just put the boat ashore now, and one side has many very small blisters. They do contain fluid that smells a bit like acid. The blisters are spread over the whole side of the hull from the water line down to 60 cm below. The other side is absolutely clean! The affected side has been parked against the quai this year. I read in another message that this can be caused by temperature differences.
: : : I have two questions: should I do something with the blisters?
: : : Next year, should I turn the boat around every two weeks?
: : : Thank and regards,

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