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Fwd: IF-41 Blisters

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  • Barbara Holbrook
    ... From: William Holbrook I also have an IF-41 built in 1977. I had a significant blister problem with large numbers in the vicinity
    Message 1 of 1 , May 21, 2013
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      ---------- Forwarded message ----------
      From: William Holbrook <wholbrook39@...>

      I also have an IF-41 built in 1977.  I had a significant blister problem with large numbers in the vicinity of the holding tank which, in my boat, was integral with the hull ( i.e., the inside of the hull formed the holding tank with no additional liner or coating in the tank).
      I was advised in my repairs by a surveyor who was formerly a boat builder in New Zealand.  

      First, a few comments on your description of your problems.  The resin "leached", no "bleached" from the glass fibers.  This is generally due to inadequate wetting of the fibers during the layup process.   Second, my boat also had many small whitish spots near the surface of the fiberglass.  The surveyor told me these were the result of dust in the mold when the first layers of glass were layed up on the gelcoat.  These do not cause a later problem if  overcoated as I describe below.  

      A final comment on how blisters form.  Fiberglass is a permeable barrier.  Yes, it is designed to be impermeable, but on a microscopic level, very few barriers are actually impermeable.  When liquids are separated by an impermeable barrier, they seek to equalize in many factors such as acidity level, etc.  Thus there is a chemical desire for the liquids to find ways to migrate through the fiberglass. When the fiberglass has imperfections, such as places not sufficiently "wetted out", these imperfections provide an avenue for the liquids to seek their balance.  When the liquids enter the fiberglass structure, they find pockets of uncured resin, resin voids, etc, and form blisters.

      Now the fix:
      I had all bottom paint an gelcoat removed by first using paint stripper, then sanding.  (I am in La Paz, Mexico, and no one here has a gelcoat stripping tool.)

      Next, on the advice of my surveyor friend, I applied VINYLESTER RESIN.  I used caps here to emphasize that vinlyester resin is the barrier which will prevent future blisters.  The surveyor informed me that vinylester resin was developed by a major university engineering school under contract to the U.S. Navy to stop the blister problems on Navy fiberglass boats.  I applied three coats using very short nap paint rollers.  I believe that the property of vinlyester resin which give it the better barrier is that it has a small degree of flexibility, even when fully cured.

      After the vinylester resin, I applied two coats of barrier coat paint -- I used a product from Pro-Line Paints, but I believe that any manufacturer's "epoxy" barrier coat would work.  I then applied three coats of hard vinyl bottom paint.  I personally do not use sloughing paints, although I understand why some people prefer them.

      My repairs were complete just over two years ago, and I have no evidence of new blisters although my boat has been in the warm waters of the Mexican Sea of Cortez.

      I hope this helps, and that you receive it in time to apply the vinlyester resin before the barrier coats.

      Bill Holbrook
      S/V Wandering Puffin
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