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

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.

Good point, Mike........one can sand and polish PU
and AU as long as
enough paint is applied. The auto painters spray on
one medium coat
and one flow coat and never want to touch it again.
Glider shops spray
on four flow coats and sand off some of the last coat
with 600W and
800W (even finer if your a fanatic) then buff it out
with liquid
rubbing compound. The PIK came with sanded PU and the
Genesis came
with sanded AU. One doesn't need to worry about over-spray
or keeping
a the wet-edge, if your going to sand it later. I often
spray one side
of a wing, let it dry, turn it over and spray the other
side after
touching the blend area with 220D. I also have found
a good PE 'white'
primer that goes on smooth and doesn't ball up like
that damned Simtec
2081.
JJ

When I repainted my ship in PU, I found a product at
the paint store from 3M called 'Guide Coat'. It is
a black powder that comes with a foam pad applicator.
You smear this on the painted surface, wet it down
with water and go at it with 600 - 800 sand paper on
a sanding pad. The Guide Coat shows the valleys between
the orange peel. When it is gone, the surface is smooth.
This stuff works so well and is so easy to apply that
I can highly recommend it to anyone who is trying to
finish sand their ship. I went back and reapplied the
guide coat between the 600 and 800 and it showed the
scratches, so it was also a good indicator of when
to stop with the 800 grit.
I was told to put extra paint on all the edges, which
I did. I still sanded through in spots. You really
have to hit any sharp contour with a LOT of paint,
as it is so easy to sand through. Then treat those
edges like a virgin when you sand. I'm very pleased
with the finished product, and would not hesitate to
do it again.
Brian Bange

There is a phenomenal amount of "reiniventing the wheel" by the glider
community in regards to this subject, and especially in regards to
painting with PU or AU. There is a tremendous amount of information
on a web site called Autobodystore.com. They sell excellent
instructional videos in addition to hosting a great Forum. As you can
see on the forum, all of these paint systems are sanded on a regular
basis by auto refinishers.

As JJ pointed out, keeping a wet edge and overspray are No Big Deal if
you plan on scuffing up the paint edge and knocking the oversray prior
to painting the rest. Alas, not everyone is aware of this -
inlcuding the high quality body shop who shot the K21 wing I spoke
of.

Refinishing a kilo-dollar glider by yourself using techniques and
materials you evolved from trial and error is not where I would get my
first experience in this type of work. Additionally, buying a
refinished glider is a bit of a leap of faith if the finish is less
than 5-ish years old. It is difficult to know how well all of the
prep and reacoating was done in less time.

The web site above is a great resource. Check it out!

Just bought 2 gal of PPG Concept AU (over 3 gal when mixed) Toyota
Super White 90288 and 2 gal of PCL Polyprimer
(white)...........................$1032.00 The control surfaces on the
DG-300 I'm rebuilding have been stripped, filled, sanded with 80g
followed be 220 dry and look good to go for painting. I use a 4 power
magnifying glass with a drop lite to spot anything I missed (old
eyes). The 80 grit scratches will disappear on the second coat and
will insure a good "tooth" is given to the paint which is important
anywhere you will be taping (wing roots).

One thing that hasen't been mentioned is a good water trap. All
compressors produce water and it must be trapped or your paint job
will be pock-marked with thousands of little craters caused when water
droplets form on the spray nozzle. I use a toilet-paper water trap and
it does the job, just replace the roll before each new
job...........................you can even dry out the old filter and
use it for its origional purpose!
Cheep-o, JJ