2:nd answer Terry Davies


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Posted by Bengt Blomberg on November 20, 2000 at 08:56:29:

Hello again Terry.
Regarding acid removal.
Some of the acid is dissolved in the styrene/glycol/water
content in the blisters and outer layer cavities.
A combination of lowering the boiling point by the vacuum
and softening of the polyester from the heat will bring
most of this acid out as you have registered. The main
part will stay put as crystals or dissolved in glycol enclosures
in the deeper laminate layers. There is no doubt that you will
succeed with first time cases where only the top layers are affected
but especially when it comes to hulls which have been treated
earlier and have sailed for some time with a barrier coat you will have
trouble again after a few years in my opinion.
The fact, that vacuum bagging has proved highly effective for removing
air and styrene blisters when molding hulls makes it easy to make yard
owners to believe in your technique, but it is a big difference in applying
vacuum to a soft uncured laminate and to a cured hard old hull.
If you have a plastic bottle filled with water and applies vacuum,
the water will be sucked out and the bottle will be pressed
together by the atmospheric pressure. If one does the same with a glass
bottle nothing happens. To discuss here why theories about boiling points being
lowered by the vacuum and capillaries in the laminate letting in air does not
work well enough would take too long.

The Duch hull had the same amounts of acid in the vacuum treated areas
as in the ones not treated. We needed the same amount of work with the
HYAB lance afterwards to get the acid out. As it is also the acid removal
which causes the bad smell, we saw no gain in combining
our techniqes.

Regarding the strength properties, any form of heating the hull to above
80 degrees C, which can be applied without deformations of the hull, will
restore the lost bond between the glass fibres and the polyester.
Bending and punching resistance will increase about 25%. Material hardness
will improve but with very variable results for different laminates.
There can't be any comparable figures presented for the techniques in
question as you keep the original laminate material where we remove a lot
of polyester from the outer fibre glass mats and replace it with epoxy.
I suggest we wait another five years from now and then compare our results
again.
Regards Bengt
Regarding the strength properties


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