Refinishing questions

Hello
I'm about to start refinishing a Discus.Searching through this and
other forums I've noticed people are leaning towards polyurethane and
away from gelcoat.Gelcoat seems to be much easier in my situation,
since I don't have a spray booth and they don't recommend sanding poly
after you've painted.I asked about PPG Concept locally and the dealer
says that acrylic urethanes shouldn't be sanded.Their top of the line
poly is called Deltron- but he couldn't say why it is better than
Concept.There's also DuPont with it's products- and they are 3-4 times
cheaper than PPG.I wonder if they really differ in quality that
much.Please advice.
Before the paint I'll have to fix one of the canopy hinges-
the rear one - it's delaminated and moves quite a bit.Pictures of the
crack are here http://picasaweb.google.com/barowicz/Canopy. How to fix
such a small detail? It seems that it takes a lot of stress and that's
why it's cracked.

Thanks,
LB

wrote in message
...
Hello
I'm about to start refinishing a Discus.Searching through this and
other forums I've noticed people are leaning towards polyurethane and
away from gelcoat.Gelcoat seems to be much easier in my situation,
since I don't have a spray booth and they don't recommend sanding poly
after you've painted.I asked about PPG Concept locally and the dealer
says that acrylic urethanes shouldn't be sanded.Their top of the line
poly is called Deltron- but he couldn't say why it is better than
Concept.There's also DuPont with it's products- and they are 3-4 times
cheaper than PPG.I wonder if they really differ in quality that
much.Please advice.
Before the paint I'll have to fix one of the canopy hinges-
the rear one - it's delaminated and moves quite a bit.Pictures of the
crack are here http://picasaweb.google.com/barowicz/Canopy. How to fix
such a small detail? It seems that it takes a lot of stress and that's
why it's cracked.

Thanks,
LB

I'm looking at the same thing you are. I've been studying the options for a
couple of years.
I've decided that gelcoat is the better option for me. Take a look at Jim
Phoenix's site where he refinishes a Nimbus 3. http://www.jimphoenix.com/

Polyurethanes are wonderful materials that are very durable and last a very
long time. In this regard, they are better than gelcoat. However,
everything depends on surface preparation and priming. You'd better get the
prep right 'cause it's hard to fix problems after you shoot the final coat.
To spray polyurethane, you really need a profesional spray booth with
professional skills and tools. It can be repaired but it's best not to.

OTOH, gelcoat is a more forgiving process - easily sprayed and highly
sandable. The refinish process is relatively simple. Just grind off the
old white stuff, fix dings, fill and contour the surface, spray gelcoat and
sand/polish to the desired finish.

Note that minor 'orange peel' and/or runs in a freshly sprayed gelcoat
surface aren't a big deal since you plan to sand off most of the coat
anyway. If you really screw up a spot, just repeat the process for that
area. Try some small projects like gear doors first so you climb the
learning curve on out-of-sight parts.

To do it right you need a clean shop with reasonably controlled temperature.
Keep in mind that a refinish can be considered a 'major repair' which
requires proper paperwork and AI sign offs. It's especially important to
keep control surface weight and balance within the limits specified in the
maintenance manual. A owner/pilot is allowed to do anything to his aircraft
that an AI is willing to sign off. Find a friendly AI before you start.

Bill Daniels

Bill, LB,

If I had to do it all over again, I'd use polyurethane. Gelcoat is
such a long process that I only got one wing, tail and part of the
fuselage done, but really it's the weight of the gelcoat that's so
discouraging. Poly-u is much lighter. Gary Kemp did his N3 in poly-u.
Definitely the way to go with all the usual cautions about spraying,
etc. Keep in mind gelcoat has it's own health problems with the
catalyst MEKP able to cause instant blindness. It's also expensive and
takes a while to get all the clever tricks learned.

Stripping and varnishing an old wooden boat seems so much easier ;-)

Jim

On Jan 6, 7:56 am, "Bill Daniels" bildan@comcast-dot-net wrote:

I'm looking at the same thing you are. I've been studying the options for a
couple of years.
I've decided that gelcoat is the better option for me. Take a look at Jim
Phoenix's site where he refinishes a Nimbus 3.http://www.jimphoenix.com/

On Jan 6, 9:13 am, wrote:
Bill, LB,

If I had to do it all over again, I'd use polyurethane. Gelcoat is
such a long process that I only got one wing, tail and part of the
fuselage done, but really it's the weight of the gelcoat that's so
discouraging. Poly-u is much lighter. Gary Kemp did his N3 in poly-u.
Definitely the way to go with all the usual cautions about spraying,
etc. Keep in mind gelcoat has it's own health problems with the
catalyst MEKP able to cause instant blindness. It's also expensive and
takes a while to get all the clever tricks learned.

Stripping and varnishing an old wooden boat seems so much easier ;-)

Jim

On Jan 6, 7:56 am, "Bill Daniels" bildan@comcast-dot-net wrote:

I'm looking at the same thing you are. I've been studying the options for a
couple of years.
I've decided that gelcoat is the better option for me. Take a look at Jim
Phoenix's site where he refinishes a Nimbus 3.http://www.jimphoenix.com/

I would second Jim's recommendation. I did the outer panels of my
Nimbus 2 a few years ago and I did it in PU. It is not that bad a
process. The nice thing is most body shops are set up to handle PU
paints. Do all the prep work yourself and then hire a local shop to
shoot the last coat of primer and paint. The work in PU is upfront,
it needs to be finished to final smoothness and shape before the
painting. The nice thing is once done you will likely never do it
again if you take care of the glider.

Search for sites that talk about finishing homebuilt aircraft like
Long-ez's, etc.

Find a good AI to work with from the start. Make sure you can do the
mass balance checks on control surfaces. I would recommended doing a
before and after as a check rather than just the after mass balance
weights.

Having done several of both, I do not see a clear answer for a
refinish.

One issue I do see clearly:

The root cause of essentially all the finish problems observed in
gelcoated gliders lies in the criminally substandard "modern"
materials used by most of the manufacturers.

There is abolutely NO reason the gelcoat finish on gliders should
fail. Gelcoated sailboats are subject to high humidity, salt water,
huge structural loads, and a lack of care by their owners yet do not
display the problems we see in our aircraft. Libelles that are 30
years old still have nearly perfect finishes. I have a gelcoated
camper shell on my pickup that has been essentially ignored and
outside for 17 years old and shows no sign of crazing or failure. I
know of several Grob products that have been out in the western USA
for 20+ years with little or no finish care and they have not
crazed.

If $100K gliders were Dodge pickups, there would be a class-action
suit filed against the manufacturers for shoddy materials.

Rant Off. Back On Topic.

"Gelcoat" Refinish (catalyzed polyester paint): Poly-Lux, Prestec,
Simtec, Vorgelat, Schwabellac (sp), Ferro, and many others

Pro's: Less skill and facilities required to apply and end up with a
good finish. Far less hazardous to work with. Easier to fix nicks
and dings. Can be profiled/contoured years after application.
Typically this can be done at least once and usually twice before
significant sand-through of the finish occurs. Less expensive than
PU

Con's: All things being equal it is not as durable as 2-pack PU,
especially if the ship is subject to environmental abuse (tied out
full-time) Requires more waxing/polishing. Subject to stress cracks
when applied thickly to floppy wings but this can be mitigated. Can
yellow with time.


2-Part Paint: PPG, Dupont, Glasurit, Imron, many others

Pro's: Very durable, shiny finish that can withstand the elements.
Does not yellow.

Con's: Very hazardous to apply (especially isocyanate catalyzed
types), Requires very good equipment, good facilities, and superior
skill to apply well. Very expensive paint systems (as much as $400
per gallon). More expensive and time-consuming to repair nicks and
dings, Cannot be profile/contour sanded after application without
repainting due to thin topcoat film thickness.

Someone mentioned that PU refinishes weight significantly less. That
has not been my experience. The PU topcoat is very thin but the
amount of primer-surfacer required to contour the surface and fill all
the pinholes in the fiberglass seem to negate any weight savings over
gelcoat. This is especially true when individuals have piled on the
primer and not sanded enough off and/or not removed all of the
previous finish.

Moisure (vapor) migration in and though epoxy composites can lift PU
topcoats due to their impermeability. Polyester coatings are porous
and allow migration.


For racing-class ships that will be taken care of, my vote is
"gelcoat".

On Jan 6, 3:24*pm, " wrote:
Having done several of both, I do not see a clear answer for a
refinish.

One issue I do see clearly:

The root cause of essentially all the finish problems observed in
gelcoated gliders lies in the criminally substandard "modern"
materials used by most of the manufacturers.

*There is abolutely NO reason the gelcoat finish on gliders should
fail. *Gelcoated sailboats are subject to high humidity, salt water,
huge structural loads, and a lack of care by their owners yet do not
display the problems we see in our aircraft. Libelles that are 30
years old still have nearly perfect finishes. I have a gelcoated
camper shell on my pickup that has been essentially ignored and
outside for 17 years old and shows no sign of crazing or failure. *I
know of several Grob products that have been out in the western USA
for 20+ years with little or no finish care and they have not
crazed.

If $100K gliders were Dodge pickups, there would be a class-action
suit filed against the manufacturers for shoddy materials.

Rant Off. *Back On Topic.

"Gelcoat" Refinish (catalyzed polyester paint): *Poly-Lux, Prestec,
Simtec, Vorgelat, Schwabellac (sp), Ferro, and many others

Pro's: Less skill and facilities required to apply and end up with a
good finish. *Far less hazardous to work with. *Easier to fix nicks
and dings. *Can be profiled/contoured years after application.
Typically this can be done at least once and usually twice before
significant sand-through of the finish occurs. Less expensive than
PU

Con's: *All things being equal it is not as durable as 2-pack PU,
especially if the ship is subject to environmental abuse (tied out
full-time) *Requires more waxing/polishing. Subject to stress cracks
when applied thickly to floppy wings but this can be mitigated. Can
yellow with time.

2-Part Paint: *PPG, Dupont, Glasurit, Imron, many others

Pro's: *Very durable, shiny finish that can withstand the elements.
Does not yellow.

Con's: *Very hazardous to apply (especially isocyanate catalyzed
types), Requires very good equipment, good facilities, and superior
skill to apply well. *Very expensive paint systems (as much as $400
per gallon). *More expensive and time-consuming to repair nicks and
dings, *Cannot be profile/contour sanded after application without
repainting due to thin topcoat film thickness.

Someone mentioned that PU refinishes weight significantly less. *That
has not been my experience. *The PU topcoat is very thin but the
amount of primer-surfacer required to contour the surface and fill all
the pinholes in the fiberglass seem to negate any weight savings over
gelcoat. This is especially true when individuals have piled on the
primer and not sanded enough off and/or not removed all of the
previous finish.

Moisure (vapor) migration in and though epoxy composites can lift PU
topcoats due to their impermeability. *Polyester coatings are porous
and allow migration.

For racing-class ships that will be taken care of, my vote is
"gelcoat".

Hey Mark,

Very thoughtful post. Quick question for you. Assuming you used
Simtec (Prestec) gelcoat, do you remember which of their formulations
you used? We (meaning glider pilots who are stupid enough to fiddle
with this stuff) seem to use the 2381 formulation, but their
literature suggests they have a formulation with additives designed to
make the finished product more flexible. Just curious whether anyone
has experimented with the various flavors of the polyester-based
products.

Thanks,

P3

I have used Simtec/Prestec 2381 and Poly-Lux which I believe are
essentially the same. Simtec will add flex agent to any of these and
to their primer-surfacer, I believe. In recent years, I have always
had the flex agent added but I have no data on its efficacy over long
periods of time nor have I done a total refinish with it - and hope to
never again. As JJ has said repeatedly, it is brutal, messy, bad-for-
you work and barely worth what one gets paid to do such labor. I know
several pilots who stripped and/or refinished their own ships. The
next time they needed such work, they got out their checkbook.

A colleague has used the Ferro (spelling?) product and is quite happy
with it. He also mixes several different brands to meet his viscosity
needs.

Real-time experimentation is tough to come by. No one I know is
willing to gamble this much money and work. They tend to stick to
known, materials, understandably.

My observations suggest that the critical factors in making a finish
last a 1) Keep the thing dry, clean, waxed and buffed. Crazing is
a shrinkage phenomena. Keep the finish "hydrated" (not water) and
it will not shrink. 2) Keep the finish thin and definitely within the
paint manufacturer's tolerances . Thick coatings tend to mechanically
crack far more than thinner ones and craze as the trapped solvents
evaporate. This is true with both polyester and PU coatings and their
primer/surfacers. The latter phenomena has come back to haunt me
in the past and is a very, very common problem in the refinished ships
I have seen. Not only is the finish more likely to crack/craze, it
makes for a heavy glider.

Assuming this is a Schempp-Hirth, you can buy new hinges. They are
screwed/bonded in and can be replaced. I have fixed several of these
in situ as well with glass and epoxy-based adhesives.

That hinge design is a major weakness that is possibly intentional so
the canopy will break away if you get the jettison sequence wrong. At
least one pilot has been beaten about the head and shoulders by a S-H
canopy that did not go away when he wanted it to.

Getting a "Pro" to shoot the last stages of a PU refinish is an
excellent idea BUT be 100% sure your "Pro" has experience painting
large objects. Most bodyshops paint small objects like quarter panels
and hoods. Painting something as large as a wing or as convoluted as
a fuselage is a whole different animal. Keeping a "wet edge" to the
paint is an art on such objects.

How do I know? We contracted out an AS-K21 wing Imron (isocyanate
catalyzed) paint job to the local high quality body guy with his world-
class spray booth and equipment and got back a finish that we had to
sand completely off and redo. I shot it the second time with
inadequate breathing gear and got a great finish and felt like crap
for 2 weeks.

Ah, the good old days!

Hello,

MG wrote:
class spray booth and equipment and got back a finish that we had to
sand completely off and redo. I shot it the second time with

The shop I was surveying the other day uses Sherwin-Williams urethane,
they have all bells and whistles, but when I asked about how they're
planning on doing a fiberglass ship
the manager said that they'll "shoot it and then put it into the oven
for some time to cure" just like
it was a truck
According to Randy Lervold http://www.romeolima.com/RV8/Paint.htm you
can shoot PU with a bit
of preparation.There is a certain amount of preparation needed but as
far as I remember, gelcoat or
any other paintjob needs good preparation.The only thing I don't like
with gelcoat is that it cracks;
however-will it really crack so bad on a refinished 20 year old glider
as on the new one if you keep it
in the trailer? In other words: how many of these cracks are stress-
imposed and how many by the resins being cured?
(and shrinking/warping of the parts)

I wish I could fix the hinge somehow, but I'm glad to hear that
they're replaceable.

Thanks,
LB