Bob,

I appreciate the feedback. We are definitely smarter as a collective
mind and I like your stuff. On the side my company has a nanotech
development that I think you will find interesting as to how it
affects composite structures. Drop me a line sometime.

Let me point out that I have seen SEM pictures of a gelcoat substrate
that did indeed have its pores closed shut by waxing. This was also
confirmed through contact angle measurements compared to a non-waxed
sample. The same energy change that forces the water to bead
externally will repel water internally away from the surface in the
same manner.

Bob, the below text in parenthesis only is your own is it not?
Taken from: http://www.wingsandwheels.com/Weathe...ock%20Tech.htm

“Effects of Porosity
Polyester gel coat appears, under the microscopic, a
very porous material. Porosity poses several problems that effect gel
coat weathering performance. First, the wall of an individual pore
increases the effective surface area in a localized area. There is
also a relatively sharp edge at the intersection of the surface and
the vertical wall of the pore. This sharp edge is subject to
photo-initiation. Second, porosity tends to collect micro-debris. This
could include general dirt, buffing compound, wax, oils etc. The
reactivity of the debris filling the porosity is a potential
problem.”

If oil can enter the pores and silicone can migrate through by pore
access, why can’t water (vapor or liquid) move into the gelcoat
substrate, which compared to these two can have a surface tension only
slight higher when conditions are right, but a smaller molecular size
than both to offset? These pores appear as garage doors to the small
water molecules? It would seem to me if water is inside and you seal
the way out, it has no where to go but in further. Add a little soap
to the water and/or increase the temperature of the water, and its
surface tension drops increasing the water’s wetting action allowing
it to penetrate the pores even easier.

For those interested DG has the following published article available
for review:
http://www.dg-flugzeugbau.de/gelcoat-e.html

Washing your glider is an unavoidable circumstance. Gelcoat can be
very permeable to water. I agree large droplets of water will not
absorb through before they evaporate. My point (which I should have
elaborated further) was that it is not that which you can remove that
will cause problems. I have to bring it up, Bob, I know you said not
to, but I have to, with the gelcoat acting as a semi-permeable
membrane and entrained moisture present (its there), add a little
hydrolysis and osmotic action exists here on a small scale for sure,
osmotic action can and does move in a small amount of H20, albeit in
only one direction, but what goes in must be able to come out
(regardless of the mode of entry) to achieve balance. If the driving
force is in, well this fundamental action is a basis for the theory of
hydraulics. (Liquids are for all purposes non-compressible). You can
seal the outside (at least we try), but current manufacturing methods
for gliders do not allow this for the internal side. With no way out
for this moisture the water has no choice but seek the path of least
resistance, which will lead to collecting in any void, SEM pictures
show that these structures are not necessarily homogeneous, so there
will be plenty of interlaminar spaces, pinholes, microscopic stress
cracks, etc. Water does freeze, vapor phase (note: vapor changes via
'deposition' like frost on the ground and bypasses liquid state
completely) or liquid phase, these hexagonal crystals just don’t fit
neatly in the same space, if left to repeat they will cause a failure.
I believe the most visible indicator of this is cracking, simply
because of the vast quantity of sanding scratches to serve as stress
risers. A rheometric measurement will support this. This was put in
place long ago. The purpose of my first posting was “to wax or not
to wax”, as such I say not waxing far outweighs the benefits of
waxing.

If we continue this let's start a new thread?

Reuben

(B Lacovara) wrote in message ...
I was actually trying to avoid this part of the discussion, but here goes…..
Interestingly enough, boat hull blistering is not a gel coat problem, but
rather a laminate problem. Considering the laminate as a semi-permeable
membrane the potential for osmosis can take place. Osmosis is the tendency of a
fluid of lower concentration to pass through a semi-permeable membrane into a
solution of higher concentration. In the case of boat hulls, water vapor (lower
concentration) passes from the inside of the hull to the outside of the hull
(higher concentration). The gel coat matrix is denser than the laminate matrix
and the transmitted water vapor will eventually collect in what are known as
seed sites. These are voids at the gel coat/laminate interface. Eventually, the
liquid in the seed sites will become denser that the outside water and the
process reverses pulling water in from the opposite direction…. This is where
the big nasty boat hull blisters appear. Blistering problems have been solved
by the boat or swimming pool industries, because they now use vinyl ester skin
coats behind the gel coat. The point is that the problem was solved with a
laminate modification, rather than a gel coat modification.

The reason I was trying to avoid this discussion, is that this mechanism is not
in play in relation to gel coat cracks. Sailplane gel coat, or more likely
urethane paint, can blister from osmosis. Just put a glider in a wet fuselage
cradle! However, until the seed site is saturated and dense there is no
transport of *liquid water*. All the moving H20 is vapor phase. This only
happens under very specific conditions. So unless you are going to ride it
hard and put it away wet there is absolutely issue with washing a gel coat
finish. But even when blistering takes place, there is no relation to typical
gel coat cracking.

Bob Lacovara