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 can we start a new thread?

Reuben


(B Lacovara) wrote in message ...
This thread has become very interesting…. there is considerable technical
discussion orbiting some of the comments. It would be nice if we were all in
the same room, where we could exchange a mass of information, rather than
simple RAS sound bites.

In too brief a sound bite fashion let me address a few of the comments:

The difference between boat gel coat and glider gel coat - It is a given that
boat gel coat holds up better than glider gel coat… many boat companies offer
a 10 year gel coat warranty! Boats are built with polyester gel coat and a
polyester (or vinyl ester variant) laminating resin substrate. The resulting
bond is a *COHESIVE* in nature. A previous comment was correct, that
essentially when boats come out of the mold they are finished (from a gel coat
cosmetic perspective - no sanding). The boats built today are using 4th and 5th
generation gel coat formulations that are fairly sophisticated. One small boat
company in the U.S. will use more gel coat than the entire glider industry.

Gliders, on the other hand, use polyester gel coat and an epoxy laminating
resin substrate. The resulting bond is an *ADHESIVE* force. The state-of-cure
of the gel coat applied in the mold at the time of laminate application is
critical to the bond. This is a complex interplay involving initiator level,
temperature, time, gel coat thickness, and other factors. There is an optimal
cure-state window for development of maximum bonding between the cured gel coat
and the laminate. At best, the adhesive bond between polyester and epoxy will
not produce as much energy as a polyester to polyester cohesive bond. The gel
coat typically used on gliders is the same basic 2nd or 3rd generation
technology as used on boats in the '70's and '80's. Also, there is
considerably more surface movement on a thin skinned glider laminate as
compared to a much thicker boat laminate.

Addressing a few of Ruben's comments - When gel coat is applied wet-on-wet, as
in the mold, it does cure as a uniform molecular matrix. When gel coat or a
paint coating is post-applied (as in repairs or refinishing leading edges out
of the mold) there is little, if any, crosslink bonding that occurs. This
scenario relies for the most part on a simple mechanical bond as Ruben
correctly stated.

Ah, the moisture issue….. It is correctly stated that gel coat and
composites laminates have the properties of a semi-permeable membrane. However
the discussion leaves the tracks with the idea of liquid water penetration and
surface porosity. *Water vapor*, that is individual molecules of H2O, will
continually seek to equilibrate on the inner and outer skins of a laminate in a
very slow process. Water in the liquid state will *not* penetrate gel coat.
The surface pores and voids in the 3-D molecular matrix are too small for
liquid phase water to penetrate. This has to do with the inherent surface
tension of liquid H2O. The surface does not wet enough for liquid to flow into
the normal porosity.

You *do not* have to be concerned about washing your glider with water, or
leaving it out in the rain for that matter. It will not have a negative effect
on the gel coat. Wax does not seal in water. Vapor phase H2O will freely
equilibrate with no noticeable retardation of transmission through a wax film.
Additionally, since liquid water is not present within the gel coat or laminate
matrix, (under normal circumstances - let's not talk osmotic blisters), there
is no issue with freezing and causing cracks. This could become an issue with
giant cracks, but not with typical gel coat effects. Freezing water is simply
not an issue.

Again, hope this helps…. After 38 rounds this thread has stayed coherent….
has to be a record for RAS!

Bob Lacovara