Refinishing: Who has tried a shortcut?

Bob

Thanks for the explanation. Do you think osmosis be a problem with gliders
such as the discus or ventus which have a wet wing.

Richard Pfiffner


"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

No, I don't think it is a issue. First the tanks are sufficiently lined.
Second, the water is not in the tanks long enough to be a problem. One would
have to leave the tanks filled for an extented period, maybe weeks?, to even
have the potential for a problem. So far I have never seen or heard of a wet
wing problem.

Bob

Thanks for the explanation. Do you think osmosis be a problem with
gliders
such as the discus or ventus which have a wet wing.

Richard Pfiffner

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

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

"Greg Arnold" wrote in message
news:y25Gb.21786$J77.6384@fed1read07...
Would gliders avoid the problem if they used the 4th and 5th generation
gel coat formulations? If so, why have the glider companies chosen to
use an older technology?


The answer is probably no. The adhesive nature of the bond would still be
inferior to the cohesive bond of an all polyester or vinylester system.
The reason for not making the change is that the current products used
conform with the type certificate and they are known quantitys with
acceptable
service lives (in the factorys eyes). Making a change introduces many
unknowns,
at least in the minds of the designers. This is a case of accepting the
current state
of affairs with the perception that changes might be more painful than
living with
todays reality.....

Scott.

I don't believe anyone has mentioned the damage that can be caused by an
inexperienced person removing gel coat.
It is very difficult work and short-cuts are tempting. Few, if any short
cuts are possible for fear of damaging the structural layers of fiberglass,
carbon or whatever.

Doing it wrong can result in an unsafe glider. For this reason, it is
probably unwise to purchase a refinished glider if it was not done by a
professional.

Tom Knauff

"Reuben" wrote in message
om...
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

Bob and Reuben,

Your postings are the first I have ever printed from
RAS for reference.

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?
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.

BTW, and in support of the opposite point of view,
I have been in the sad position of monitoring a friend's
Std Cirrus that has not been out of its metal non insulated
trailer in Scotland for 10 years. The fuselage was
rebuilt in about 1981 and painted in vorgelat. The
wings are original Scwabbellack. 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?

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.

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

John Galloway

B Lacovara wrote:

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.

Would gliders avoid the problem if they used the 4th and 5th generation
gel coat formulations? If so, why have the glider companies chosen to
use an older technology?

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

Reuben wrote:
What would the group here say this flier flies
in a calendar year? 50 hours, more? If I chose 50 hours added 25
percent (for time not spent flying, rigging, staged on the line and so
forth) to represent the time of total exposure to the UV for the year.
That is 62.5 half hours for that year, right? At the end of ten years
we would have 625 hours. Not quite a month's worth of continuous UV
exposure. What about 20 years for this owner. 1250 hours. Just shy of
two months of continuous exposure. If your topcoat of choice can't
handle that, Oh boy. What about in your region's winter months when UV
intensity is generally at its lowest level. Hmmm.

A pilot that flies his glider only 50 hours a year probably should think
about selling it or getting some partners! Maybe he doesn't have to
worry about UV. Let's a take my situation:

-200 hours a year of flying (about 40 hours above 10,000 feet)
-tied out all day for about 1 week in summer at low altitudes
-tied out all day for about 2 weeks in summer at high altitudes (5000+ feet)

Breaking it down:

140 hours flying but kept in trailer
60 hours being rigged/derigged (4.5 hour flights, 30 flights)
60 hours flying but kept outside
140 hours exposure while tied down
---------
400 hours a year UV exposure - 6.4 times Reuben's example

And, many of these hours are at high altitudes in clean air, where the
UV will be much more intense.

So, should I be worried about UV exposure? When I polish my glider, I
notice the top of the wings makes my polishing rag turn white sooner
than the bottom of the wing. I believe this because the gel coat on the
top is suffering more than the gel coat on the bottom, and my guess is
it's UV.

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Eric Greenwell
Washington State
USA