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 outs, but t
hey 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
