Bill,
You are right about letting oil modified urethanes cure for an extended period
of time before applying fabric. This is true of any varnish that cures by oxidation.
Epoxies or 2 part urethanes cure by an entirely different chemical process
and should be ready for covering in 24 to 72 hours. As for the oil modified
varnishes, one month would be plenty of time. You may be able to cover sooner,
depending on the thickness of the applied varnish and the temperature in the
room where the parts are kept. Its best to coat a scrap of wood exactly the
same as the part being covered. When the test piece is capable of passing the
30 minute MEK or lacquer thinner test, then you are good to go.
I am very aware of the Stewart's water based system. Dan and Doug Stewart are both
members of the Short Wing Piper Club as I am. I have attended their covering
seminars and have a copy of their covering DVD set and I am impressed! If my
facts are straight, the adhesive and primer parts of their water based system
have been around for a number of years and have worked quite well. The top coat
part is relatively new, but the entire system is certified. I do have some
familiarity with how the products are formulated and I think they will perform
OK. I plan on probably using their system at least up through the primer and
maybe the entire way.
Rick Schreiber
Valparaiso, IN
5936D PA22-150
----- Original Message -----
From: Bill Church
To: pietenpol-list@matronics.com
Sent: 11/25/2008 11:54:11 AM
Subject: RE: Varnishing Wood
Now, there's an educated reply. Thanks for sharing your knowledge, Rick.
I just recently finished "varnishing" my empennage with Minwax's Spar Urethane.
I noticed that the can had a note indicating that the product was "improved",
and was now quicker drying. That obviously means that the formulation has been
changed. What it doesn't say is whether the newest "improvement" results in
a more durable finish (the sticker on the lid of the can did not claim it to be
more durable, so I doubt that it is). I recall postings from a few years ago
that implied that hardware store urethanes are much less impervious to solvents
if one attempts to cover soon after sealing, as the finish has not fully cured.
As I recall, it was suggested that the urethane be allowed to cure for at
least a month before applying solvent-based adhesives (hope my memory is working).
I have recently been thinking that the Stewart's water-based adhesives sound like
a good idea, and may be the route I take when I get to that stage of building,
and I read recently that Kitplanes magazine is planning to publish an in-depth
review of the products. From what I have read, the Stewart's products work
as well as, if not better than the traditional systems. The disadvantage, at
this point, is the relative newness of the system, and the lack of a long-term
proven track record.
I have no doubt that, with the way things have been going, practically all solvent-based
products will become increasingly more rare, if not banned outright.
Some may say that the traditional finishes will never be replaced, but I can
recall just a few years ago, hearing many people say that they would never be
able to restrict cigarette smoking. Same story with leaded gasoline. Change is
coming, like it or not. The good thing is that someone is working on solutions
now.
Bill C.
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 ... .
Rick Schreiber
Valparaiso, IN
