[alberg30] Re: Osmotic Blisters

[George Dinwiddie]

From: George Dinwiddie <gdinwiddie at min.net>

Peter,

All Alberg 30's, like virtually every other boat of the vintage, are
built of polyester resin.  Osmotic blisters, however, have not been
a major problem with the boats.

Polyester resin and gelcoat are not entirely impervious to water.
There are chemical compounds left in the resin that are soluable in
water.  Osmotic blisters are caused by these compounds soaking up
water and being trapped in the resin.  The area swells until it 
pushes out a blister, causing a small delaminated area.

It's my opinion that our boat, built in 1973 during the energy
crisis, has a relatively permeable gelcoat that generally allows
these compounds to pass back out.  We tend to get small (pea-sized)
blisters in the bottom paint (Pettit Trinidad, a hard paint), but
not much in the gelcoat itself.

If you do have a few blisters, you can take the same approach that
is used in virtually all plastic boats built in the 60's and 70's.
That is to grind out the individual blisters and fill with thickened
epoxy to fair the hull.  This is a relatively simple thing to do
and the Alberg hull will still be plenty strong.

If you have a lot of blisters (usually only if the boat is left 
in the water constantly for a lot of years) or are worried about
it, you can sandblast or peel the gelcoat and hydrolyzed resin
off.  Then let the hull dry *thoroughly* (or you'll have a worse
problem) and fair the hull.  Finally apply a barrier coat over
the new fairing.  This is not a trivial job, but not entirely
overwhelming.

Talk to some fiberglass people in your area and get a bunch of
different opinions.  Keep in mind that they make money by
suggesting big jobs, so keep a little scepticism.  But don't 
get too worried.  There have been some boats with a serious
history of blister problems (e.g. the Valiants with the 
fire-retardant resin), but the Alberg 30 isn't one of those.
It's just not immune to the problem, either.

I hope you find the boat of your dreams,
   - George

-- 
 ----------------------------------------------------------------------
  George Dinwiddie                                  gdinwiddie at min.net
  The gods do not deduct from man's allotted span those hours spent in
  sailing.          http://ourworld.compuserve.com/homepages/Alberg30/
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