Good post, Rick. Nice to hear from someone who actually is an expert on
the subject.
I used PolyFiber's 2 part epoxy varnish on my Pietenpol. Since the
landing gear struts are exposed to sunlight any time the plane is out of
the hangar, what should I look for in UV degradation? Will I notice a
yellowing, or a change in clarity? Of course, since the plane spends
most of its life in a hangar, the changes may take years to appear. The
longest period of continuous use outside a hangar is the occasional trip
to Brodhead.
Jack Phillips
NX899JP
_____
From: owner-pietenpol-list-server@matronics.com
[mailto:owner-pietenpol-list-server@matronics.com] On Behalf Of Richard
Schreiber
Sent: Tuesday, November 25, 2008 11:33 AM
To: pietenpol-list
Subject: Varnishing Wood
I have been reading the posts recently on varnishing wood with interest
and would like to add my 2 cents to the discussion. First a little
history. I have worked in the coatings industry for over 35 years
serving as a Technical Director for various paint companies supplying
coatings to the international market. I now own my own paint company
supplying high performance coatings to the firearms industry.
The formulations used for wood varnish, have been in a state of flux for
the past two decades due primarily to mandates from Congress, the
Environmental Protection Agency and cost considerations. This has been
especially true for the last 10 years. In order to meet the current
environmental regulations for low solvent content, manufacturers have
had to dramatically reformulate their products. The old non-urethane
based varnishes were made by cooking various seed oils, such as linseed,
tung, soybean etc., with resins. This was a costly process and based
more on art than any real science. These cooked varnish formulations
began to be replaced by the urethane varnishes in the 50's. By the 70's,
this replacement began to accelerate. This was due to the superior
performance and ease of manufacture of the oil modifed urethanes. By the
late 80's the replacement of the old cooked varnishes with the oil
modifed urethanes was almost complete. Their may have been a few hold o
uts, but they were relying on perceived quality not on fact. By the mid
to late 90's there were many oil-modifed urethane varnishes on the maket
that far surpased the old style vrnishes in quality. These oil- modified
urethane varnishes dried faster, had better flexibility, better color
retention and much better resistance to UV degredation than the old
style varnishes. Many of these oil-modifed urethanes were more than
adequate for varnishing wood aircraft, no matter what finishing process
was used. In the late 90's Mike Cuy picked a good one from Minwax for
his plane. Others in the past, have used spar varnish from ACE hardware
with success . However, as I stated before, these formulations have
changed dramatically in the past 10 years, to satisfy the current VOC
regulations and probobaly would not pass the 30 minute lacquer thinner
test.
I certainly do not have access to the competion's formulas, but I know
what I have had to do to my formulations in the past to satisify these
regulations! None of the changes are good for aircraft wood varnishes.
This especially true when it comes to solvent resistance. If it were me
(which it is as I am in the varnishing stage on my Piet) this is what I
would do.
1. If you are finishing with a system that contains strong lacquer
solvents such as Stits, Randolph etc., varnishing with a two part epoxy
would be a good option. Just be aware that epoxies have very poor
resistance to UV light and the coatings are expensive and somewhat
difficult to apply.
2. If you finish with the Stewart's water based system, you have more
options. Since solvent attack is not an issue, most of the currently
available exterior grade oil modified urethanes would be OK.
3. This is the process I am going to use. This is not ment as an
advertisement, its just what I have done. Since I manufacture and sell
high performance varnishes for firearms, this is what I have used on my
Pietenpol. Our Permalyn finish was designed for exterior use, with
flexibility and resistance to gun cleaning solvents in mind. I have
tested for resistance to strong lacquer solvents with a 30 min soak and
it passes just fine. For those that might be interested here is a link
to information on the varnish
http://www.laurelmountainforge.com/finish.htm.
For anyone who wants to call me direct call at 219-548-2950, 9-5 CST.
Rick Schreiber
Valparaiso, IN
lmforge@earthlink.net
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