Again, apoligizing for limited sound bites of information, but it's the best we
can do in this forum........

When addressing the question of to what extent liquid water can
penetrate a gelcoat surface and whether or not to wax, would either of you be
prepared to comment
on whether reduction of gelcoat surface deterioration by using a UV filtering
polish (e.g. Wx/block + Wx/seal) will have a significant effect on the ultimate
advice?

From my perspective, the potential of gel coat damage from liquid state water
is minimal, and is a secondary debate. We have conducted tens of thousands of
hours of testing within the composites industry on gel coat weathering
performance. A narrow band within the UV spectrum range is the primary source
of surface degradation. Thousands of hours of testing have also shown that
surface degradation can be significantly slowed with the routine application of
a UV inhibited surface agent. Please understand that as the original developer
of the Wx/Block & Wx/Seal products I could be viewed as being bias in this
portion of the discussion. However, my goal is to offer valid science without a
commercial bias. The data on waxed vs. non-waxed gel coat surfaces indicates a
UV effective wax significantly delays color change and the results of
photo-oxidation. Better than test results, we seem to have a good history over
the last 10-years with maintaining gel coat finishes by using an UV effective
wax.

Apart from crazing a non waxed weathered vorgelat gelcoat also eventually
goes dry and powdery and looks and feels like it would soak up liquid water
into its
surface layer more easily than a highly polished and uv protected (by polish or
covers/hangaring) gelcoat.

This is typically the effects of photo-oxidation that causes molecules to sluff
off the surface. Polishing "wets" the surface and reduces the powderly look,
while consolidating the loose micro-particles.

Both were fine in 1993 but since then, in the dark, the fuselage has
crazed dramatically and became dull and powdery so that (before I polished it a
year or so ago) you could get your clothes white by coming into contact with
it. This expensive unintended experiment confirms that gelcoat can definitely
detriorate very badly in the virtual absence of UV. Is this just moisture or
does vorgelat gelcoat just molecularly age no matter what?

Gelcoat is a very quirky coating, no doubt. This phenomenon is known but not
currently explained. It is technically termed "box yellowing". There is a very
different mechanism at work here…. something different than UV degradation.
We postulate it may have to do with a reduced crosslinking density at the time
of original cure; I am currently part of a technical task force studying this
specific problem. To date no results - the first round of testing by the gel
coat manufacturers did not yield conclusive data.

It would be fascinating to store gelcoat glider samples in a typical
glider trailer in the dark - some polished and some not - and to see whether it
polish does or does not prevent moisture and temperature gelcoat deterioration
in the absence of UV.

It would be a great experiment, but to be meaningful there would have to be a
large enough sample group to avoid jumping to conclusions based on anecdotal
evidence.

Supplementary question - if cost was not an issue would you get a new
glider painted in PU or T35?

In my opinion, a linear polyurethane paint (properly applied) is better than
gel coat on gliders. For what it's worth my glider has factory finish PU.

Bob Lacovara