Re: Wet spots - no blisters


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Posted by B.B. on February 14, 2005 at 03:33:57:

In Reply to: Wet spots - no blisters posted by Guido Pas on February 14, 2005 at 03:31:53:

Posted by Bengt Blomberg on January 09, 2003 at 09:41:22:
In Reply to: wet spots, no blisters posted by Guido Pas on January 06, 2003 at 09:03:39:
: Last year I have bought a 30 year old one tonner. It was built in Greece and the hull is +/- 3cm thick. The previous owner told me that the hull was wet and advised me to dry it and apply an epoxy coat. He thinks the gelcoat has become very thin over the years. The boat has been on shore for the last 1,5 year due to other reasons. During that time I had someone test the moist content several times. Most of the ship is fairly dry (
Hello Guido,
It is not the blisters that are dangerous! They are a sign that an hydrolysis is proceeding only.
If the gelcoat is thin and old, in many cases there will be no blisters at all and the laminate can become totally soft before the owner becomes aware of the problem.
What happens is, that the hard polyester gradually get hydrolysed into its original fluid substanses until at the end there will be soft fiberglass only left.
There exists nothing like "preventive" treatments!!! So called moisture barriers is a waste of money only and do more harm than good.
Any submerged laminate contains at least 0.2% moisture which is sufficient to feed the process even if it does not cause any alarming figures on the moisture meters.
The high moisture readings comes only when the hydrolysis has caused voids and glass layers without resin where excess water can enter. THE PROBLEM IS ABSOLUTELY NOT CAUSED BY THIS EXCESS WATER ENTRANCE and it does not cause any acceleration of the damages! Instead it cools and slows down the hydrolysis.
The only way to stop hydrolysis of polyester is to perform a treatment which removes the substanses which cause it. If that can not be afforded it is better to do nothing else than normal sanding and antifouling painting for as long as the hull stays solid enough. Then it will last much longer with less damages than if only dried and epoxy coated.
In your case you can easily check if you have an hydrolysis or not: Drill a few holes with the tip of a 1/2" drill bit through 3/4 of the laminate thicknes in the areas with the highest readings and check the pH value with a blue lithmus paper strip which you can buy in a drugstore. If there is acid from the process in the hole, the paper will become red. If it stays blue, white or slightly yellow, the laminate is a little more porous in that area only.
Also check at dry setting if the props deforms the hull anything. That is the first alarming sign for hulls which do not blister.
Regards Bengt


: Posted by Guido Pas on January 06, 2003 at 09:03:39:
: Last year I have bought a 30 year old one tonner. It was built in Greece and the hull is +/- 3cm thick. The previous owner told me that the hull was wet and advised me to dry it and apply an epoxy coat. He thinks the gelcoat has become very thin over the years. The boat has been on shore for the last 1,5 year due to other reasons. During that time I had someone test the moist content several times. Most of the ship is fairly dry (




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