Answer to Jack Groot

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Posted by B. Blomberg on September 27, 2000 at 11:28:09:

Sorry Jack,
I see that my answer to you last week has not gone through.
Here it is again:
Modern core foam have closed cells and does not absorb more
moisture through the outer laminate than what evaporates
through the inner laminate.
High moisture readings mostly have one or both of two reasons:
1. For very curved hulls the foam planes are often cut
almost through in sugar lump forms on the side attached
to the outer laminate in order to allow bending without breaking.
When the plane is pressed against the hull the cuts opens to
spalts. Normally the planes should be bent and the spalts
filled with resin before applying to the laminate but this
is seldom done. After launching these empty spalts fills
with water within a few months and then never dries.
In cold salt waters and long winter dry settings this mostly
has no damaging effect to the laminate.

2. The rough surface of the foam penetrates a lot of not cured
polyester/styrene enclosures which forms between the curing
laminate and the foam when the surplus styrene can not
escape through the foam. Therefore there are always lots
of hydrolyse triggers in the last laminate layer against
the foam. In sweet water temperatures of over 18 degrees C
and tropical salt waters This layer will almost always
have the polyester hydrolysed and delaminate from the foam.
The delamination contains a mixture of water, acid and glycol.
The acid causes the hydrolysis to proceed outwards in
the laminate.
As a delamination between laminate and core causes a
60-70% loss of structural strength I recommend you to drill
10 -15 test holes through the outer laminat and see if
the last laminate layers are darker coloured and also use a
blue litmus paper strip to check the acidity.
If there is acid, there are only two ways of repair:
A HYAB treatment or to peel of the total outer laminate
and replace it with an new epoxy laminate of 1x600 and 2x300 g
3 shaft E-glass mats after cleaning of the foam surface.

Regards Bengt Blomberg

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