another gelcoat story

On Aug 24, 9:28*am, Brad wrote:
Propane releases moisture during combustion...

Correct me if I'm wrong, but I'd expect that oxidizing propane would
only release moisture into the exhaust gasses. My heater setup vents
all of the combustion exhaust gasses outside the building. I figure
it'd have to, or else we'd all have died from CO poisioning by now.

Thanks, Bob K.

On Aug 26, 2:09*pm, Bob Kuykendall wrote:
On Aug 24, 9:28*am, Brad wrote:

Propane releases moisture during combustion...

Correct me if I'm wrong, but I'd expect that oxidizing propane would
only release moisture into the exhaust gasses. My heater setup vents
all of the combustion exhaust gasses outside the building. I figure
it'd have to, or else we'd all have died from CO poisioning by now.

Thanks, Bob K.

Was Brad using a Space Heater, or a forced air gas furnace like you
have? I wouldn't think your heater would be a problem.

On Aug 26, 4:18*pm, Uncle Fuzzy wrote:

Was Brad using a Space Heater, or a forced air gas furnace like you
have? I wouldn't think your heater would be a problem.

Brad laid up his fuselage shells at my shop, using my shop heater, not
a space heater. It's a Modine Hot Dawg 75 kbtu unit I put up several
years ago.

In the past I've used kerosene and propane space heaters, but mostly
just with quickie polyester/glass layups. Those things give me the
willies, I'm always worried about carbon monoxide poisoning.

Thanks, Bob K.

On Aug 26, 5:07*pm, Bob Kuykendall wrote:
On Aug 26, 4:18*pm, Uncle Fuzzy wrote:

Was Brad using a Space Heater, or a forced air gas furnace like you
have? I wouldn't think your heater would be a problem.

Brad laid up his fuselage shells at my shop, using my shop heater, not
a space heater. It's a Modine Hot Dawg 75 kbtu unit I put up several
years ago.

In the past I've used kerosene and propane space heaters, but mostly
just with quickie polyester/glass layups. Those things give me the
willies, I'm always worried about carbon monoxide poisoning.

Thanks, Bob K.

That's what I thought. Unfortunately, that kinda' decreases the
chances that excess moisture in the air caused the epoxy not to bond
to the gelcoat.

On Aug 26, 9:02*pm, Uncle Fuzzy wrote:
On Aug 26, 5:07*pm, Bob Kuykendall wrote:

On Aug 26, 4:18*pm, Uncle Fuzzy wrote:

Was Brad using a Space Heater, or a forced air gas furnace like you
have? I wouldn't think your heater would be a problem.

Brad laid up his fuselage shells at my shop, using my shop heater, not
a space heater. It's a Modine Hot Dawg 75 kbtu unit I put up several
years ago.

In the past I've used kerosene and propane space heaters, but mostly
just with quickie polyester/glass layups. Those things give me the
willies, I'm always worried about carbon monoxide poisoning.

Thanks, Bob K.

That's what I thought. *Unfortunately, that kinda' decreases the
chances that excess moisture in the air caused the epoxy not to bond
to the gelcoat.

The process the factories use has developed over quite some time.
Important factors include:
1) The exact chemistries of the gelcoat and epoxy being used. These
are chemically disimilar materials being asked to form a "permanent"
bond during curing.
2) The timing of the process. The time from when gelcoat is sprayed
and has gelled- but not cured- to when the first application of epoxy
is important to getting whatever "bond" you get between materials .

Using a developmental process with different materials will obviously
require a good bit of testing.

Another option could be to skip the whole gelcoat thing and do the
lamination of epoxy/glass/carbon directly in the mold and accept that
it will need pinhole/prime/fill and then paint. You would avoid the
time delay failure mode that gelcoat finishes have inherent to them.
They all fail- its only a matter of time till the gelcoat comes off in
sheets or chips.

FWIW
UH

wrote:


Another option could be to skip the whole gelcoat thing and do the
lamination of epoxy/glass/carbon directly in the mold and accept that
it will need pinhole/prime/fill and then paint. You would avoid the
time delay failure mode that gelcoat finishes have inherent to them.
They all fail- its only a matter of time till the gelcoat comes off in
sheets or chips.

It's all about the duration, though:

Time = 5 years = angry owner
Time = 50 years = happy owner(s)

Do the factories offering polyurethane paint as an option to gel coat
still use a thin layer gel coat? How much does that method extend the
life of the gel coat?

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

On Aug 27, 1:37*pm, Eric Greenwell wrote:
wrote:

Another option could be to skip the whole gelcoat thing and do the
lamination of epoxy/glass/carbon directly in the mold and accept that
it will need pinhole/prime/fill and then paint. You would avoid the
time delay failure mode that gelcoat finishes have inherent to them.
They all fail- its only a matter of time till the gelcoat comes off in
sheets or chips.

It's all about the duration, though:

Time = 5 years = angry owner
Time = 50 years = happy owner(s)

Do the factories offering polyurethane paint as an option to gel coat
still use a thin layer gel coat? How much does that method extend the
life of the gel coat?

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes"http://tinyurl.com/y739x4
* * * New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" atwww.motorglider.org

The painted gliders still come out of the mold with gelcoat. It gives
them something to sand and provide basis for finish.
Life isn't known yet because the aren't that many out there with
original PU finishes. It has only been commonly available, as far as I
know, for maybe 5 yrs. If you can keep moisture and UV away from it, I
would expect gelcoat to last quite a while, certainly longer than
"natural" gelcoat.
All this said, we have a Std Libelle in our club which is over 35 yr
old and the finish on the wings(original) is still excellent.
We also have an ASK-21 which is about 25 yr old which I expect we will
be able to take the gelcoat off with a chisel(don't ask) in chunks.

Do the factories offering polyurethane paint as an option to gel coat
still use a thin layer gel coat? How much does that method extend the
life of the gel coat?

Yes, it is necessary to use gel coat or an in-mold primer gel coat. As
Hank mentioned it is not practical to laminate directly on the mold
surface. The laminate will be full of pinholes and require extensive
post-mold priming and sanding before a finish coating can be applied.
Now here's a catch 22 - It is not feasible to apply a "thin" layer of
polyester gel coat. The normally recommended wet film thickness ranges
from a low of 14 mils (mil =.001") to 18+ mils. With anything thinner
than 14 mils the proportional amount of styrene lost through
evaporation becomes so high that there is not enough styrene left for
complete crosslinking. Bottomline - overly thin gel coat will be
permanently under-cured regardless of catalyst level or curing
temperature.

A linear urethane topcoat will extend the life of a well applied gel
coat substrate condsiderably.

Bob

"Bob Kuykendall" wrote in message
...
On Aug 26, 4:18 pm, Uncle Fuzzy wrote:

Those things give me the
willies, I'm always worried about carbon monoxide poisoning.

Thanks, Bob K.


As well you should be!

Carbon Monoxide detectors are available and inexpensive. They look like
smoke detectors.
Pilot shops sell CO detectors for the cockpit.


Insidious and deadly. Use extreme caution.

Hartley Falbaum