To expand a little oops, A LOT
Polyurethanes like Imron make a great "wetlook" finish but they along with most
other paints loose their plasticisers ("dry out") after time. Also because
polyurethanes are a completely different paint family from dopes and polyfiber
products ("dopes"), they "shrink" with changes in temperature at a different
rate than "dope" type products and therefore loose their bond to the "dope"
type substrates.
Polyfiber is still in the dope family, basically an acrylic lacquer with lots
or plasticisers. Don't believe it? spill a little lacquer thinner on polyfiber
and it will disolve like paint stripper.
I also think polyfiber is a great product but some of the newer waterbased
products may prove to be as good or better.
The application process may not be as much fun though, that is where the term
"dope head" originated. Guys that painted planes acted more than a little goofy.
(Funny story, years ago when I lived in town and was recovering a J-5 Cub
Cruiser in my garage, kept seeing police cars in the alley behind my house.
Finally walked out and asked if there was a problem. He said ther were reports
that I was shipping in "dope". Told him I was, by the 5 gallon can.)
There is a process with an STC that uses a polyurethane base directly on the
fabric with LOTS of "flex additive" and a polyurethane topcoat. It was based on
the Dupont durethane line. Haven't run into any planes finished with this
process. It still can't be rejuvenated and is good for about 10 years in the
sun, much more if hangared.
Once any enamel based paint starts cracking you are looking at a recover job or
as stated a strip and repaint. This is really a shame because the underlying
fabric and base is probably ok. Having done both, the strip is a real pain but
you are not required to be an A&P to paint an airplane without ballanced
control surfaces (like our coupes)
The alternative is to fly like it is till the paint falls off. You are still
airworthy, just don't want anybody to see you in it. The topcoat is only
cosmetic. As long as you can look up thru the many inspection panels and not
see daylight where the paint is cracking and the fabric punches OK you should
be airworthy.
Gosh, must be taking lessons from the other Bill.
Bill Biggs
Date: Mon, 12 Oct 2009 18:32:41 -0500
From: [email protected]
To: [email protected]
Subject: Re: {Disarmed} RE: [ercoupe-tech] Re: Paint Cracking
Unless it's Polyfiber, in which case, use their recommended product - NOT dope.
Dope is fine for Ceconite, cotton, etc. just not Polyfiber
Bill's right, you get the picture.
Bill BIGGS wrote:
As a temporary fix, put super glue along the crack, then put wax paper on it
and rub along the crack til the super glue dries.(it won't stick to wax paper.)
Your topcoat has lost it's plasticisers, and polyurethanes can't be rejuvenated.
If the crack is spanwise it is time to recover, or with luck try peeling the
polyurethane off and sand and repaint with DOPE.
Sorry,
Bill
To: [email protected]
From: [email protected]
Date: Mon, 12 Oct 2009 13:57:58 -0400
Subject: [ercoupe-tech] Re: Paint Cracking
Bob,
How do you know your wings are painted with Imron? How long has it been since
they were recovered? What fabric and recovering process was used? All of these
issues impact your decisions about a failing paint job.
When I bought my coupe the wings were finished in a high gloss paint that
looked suspiciously like an automotive paint. The paint had started to crack
and I bought the plane knowing that the wings would soon need recovering. I
inquired around to see if the paint could be repaired. The first step seemed to
be to determine what paint is actually on the wing. I was told the process to
accomplish this involved using various solvents to discover the actual finish.
In my case, the log book indicated the wings had not been recovered for quite
some time so I decided to fly it for a while (after it was approved for flight
by an IA) and then just recover the wings at a convenient time. Unless the
paperwork contains a 337 and an STC defining the last covering process used, I
don't know that I would trust a plain logbook entry for identifying materials
used during a recovering and/or paint job. While just a paint job may not
require a 337, I believe a recovering does require one. In the case of the
cracking paint, the IA seemed to feel that as long as the fabric under the
paint was not weakened by exposure to water or the sun, it would be safe to
fly. However, I could see that the cracks were increasing in number and small
patches of bare fabric were becoming exposed to the elements.
I ended up doing my wings myself under the supervision of an IA. I enjoyed
learning the process. And I gained the additional comfort of knowing the wings
structure is currently corrosion free and well protected by the two part epoxy
now in use. I also had the chance to smooth out the dings in the leading edge
that the plane acquired over the past 60 plus years. I suggest you look around
and find an IA that you can work with and use his knowledge and expertise to
diagnose and fix the problem with your wings.
John Roach
N 2427H
Bob Stearns wrote: My fabric wings are painted with Imron. I just noticed a
hairline crack, curved maybe 3 inches long, above one of the ribs. Should I
worry unduly? Can it be repaired? Stop drilling is out of the question <vbg>.
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