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Bruce[_4_]

On Thu, 25 Mar 2010 21:50:05 +0100, (Martin
Schöön) wrote:

Bruce writes:

On Wed, 24 Mar 2010 20:20:45 -0700 (PDT), Frogwatch
wrote:

Say you want to drive the moisture out of gelcoat. I've used a heat
gun to do it and was surprised at how much water came out.
So, what would a high power microwave unit do? Water absorbs the
microwaves much better than the polyester so it would get hot and come
out. This would avoid the months of waiting for a hull to dry if you
are repairing blisters (a real scam as blisters are not a real
problem).

Some years ago I read, in one of the boating magazines, about a guy
that had invented an innovative method of drying a hull. He removed
the door from a micro-wave oven and bypassed the "door-open" safety
switch. Placed the oven face down on the deck and turned on the power.

Innovative and dangerous.

I never read anything more about the method and have visions of him
heating the saturated deck core to the point that steam was generated
and the resultant upheaval.

Water when heated turns to steam and I can assure you that the steam
will come out :-)

Heat the laminate + water quick enough and you create blisters. This is
one of the quality assurance tests of printed circuit boards. Too much
moisture (which is much, much less than found in any boat laminate) or
poor laminating quality (still much better than you hand layup boat
laminate) will cause blisters. OK, that test involves much higher
temperatures than what you are likely to subject your laminates to.

Bear in mind that high temperatures degrade laminates.

Why not try the kind of equipment used to dry out buildings that
got drenched one way or another? It may not be as innovative but
also much less likely to damage your boat or indeed yourself.

/Martin

I recently read an article in one of the boating magazines - Practical
Boat Owner - that discussed osmosis repairs. They noted that while the
old method was to tent the hull and install infrared or plain old
electric heaters to dry the hull. This was, of curse, in English
weather. The article went on to say that this is no longer done
because in practice it was not effective as they stated that the real
problem in osmoses is poorly cured resins which absorb water.

Whether this is the final word in osmosis treatment I don't know
however I did recently did a fairly extensive treatment of osmosis on
a 40 ft. sail boat, built in 1971. We ground out all the blisters,
pressure washed with water two times letting the surfaces dry between
washes, washed with acetone, and filled the blisters with chopped mat
and polyester resin. Sanded smooth and then rolled two coats of epoxy
on the entire underwater portion of the hull.

Some time later the boat was surveyed and the Surveyor took moisture
readings every foot and the moisture content was nearly constant from
the top to the bottom of the hull, and fell well within the "good"
portion of the meter dial.

Whether this is a valid test I'm not sure but it certainly cured the
blisters :-)

Cheers,

Bruce