John Galloway . uk wrote in message ...
At 16:00 21 December 2003, Jj Sinclair wrote:
Oh My, Ruben
It sounds like we have finally found someone who actually
knows what they are
talking about. Your post brings up several questions:

for example when you wash your glider, then dry it
and finally wax
it (because it is all clean now, right?), your drying
was never really
able to extract the water from the pores.

Should we be waxing gelcoat? How about urethane finishes?

I have seen little blisters that form when a sailplans
is left in a very wet
environment, like a metal trailer. When these blisters
are popped, a little bit
of water is evident under each blister. I have seen
this in urethane and also
in gelcoat (Prestec) What is your take on this?

JJ Sinclair

Ruben's post is really interesting and he makes a very
strong case for water exerting a damaging shear force
between phsically bonded coating layers a refinished
glider and for exacerbating cracking - but is it the
whole story for gliders with their original finish?
I think Bob Lacovara also knows what he is talking
about - see his posting of 04-42 on 6th December and
also his article (and qualifications) at:

http://www.wingsandwheels.com/Weathe...ock%20Tech.htm

I will take a lot of convincing not to cover my glider
with a UV protectant wax and, preferably, to have a
PU finish to reduce the risk of surface crazing from
UV degredation.

Having suffered badly from water filled blisters on
one glider I am very conscious of the effects of moisture
but it seems, from what is written about experiences
in the boating world, moisture will get in through
the composite structure to the gelcoat from the inside
out in wet conditions. The boating people say that
the water dissolves chemicals out of the resin on its
way through and that the water in the blisters tastes
chemical but when I tried it on water from our Discus
fuselage blisters it was pretty tasteless.

The boats are buildt of polyester. The hardener is an acid. In the
cured polyester there can be small amounts of acid that react with
water. That is why the water coming out of these blisters smells and
tastes chemical. Gliders are buildt whit epoxy that does not react
with water the same way. Polyestergelcoat is not a very good barrier
for water. That is why many boats are painted, under the waterline,
with an epoxybased primer.

Matts, glider pilot and boatbuilding teacher


For crazing I think that UV surface damage top old
gelcoat is the main enemy and water can then start
to penetrate from the outside. Meantime, in damp conditions,
water has been penetrating from inside from new and
this can cause blisters even in gliders with less porous
coatings

So my plan is to get a PU finish, use Wx Seal/Block
during really dry spells of weather to keep the external
surface as impervious to water and UV as possible and
to store the glider in as uv-free dry conditions as
I can achieve.

John Galloway