Due to the number of people on this board mucking around with their SAR-1 furniture,
I thought I'd write up an article to talk about various finishing options. I originally
poseted this on AK-47.net.
I assume that we're starting with the "as-is" wood that was on the rifle. If you're really
interested in wood finishing, I suggest the book "Understanding Wood Finishing" by
Bob Flexner. It is an excellent reference. Lots of books will tell you to finish
a certain wood always in a certain way, because "it's just done that way". But wood
finishing is a very personal thing, and not everyone likes the same result. With that
in mind, I do have several hard opinions which you may choose to disagree with:
1) Oil, or Oil/Varnish blends (most Watco, Formby's, "rubbing" finishes, etc.) are
NOT the best way to finish wood on rifles. Yes, they're easy to apply and they do
look good, but they are not a very protective finish for a rifle. If it's on display,
OK, but if you're going to shoot it a lot, then oil is not your best choice. Oil
penetrates, but don't be mislead to think that that equals protection from moisture.
"Boiled" linseed oil isn't really an oil, but linseed oil to which driers
have been added. It cures in about 1 day. I'll quote Flexner's
book here: "Of all finishes except wax, linseed oil is the least
protective. It's a soft, thin finish, so it provides no significant
barrier against scratching. It's also easily penetrated by water
and water vapor. Liquid water will penetrate through a linseed oil
finish and cause a smudge within 5 to 10 seconds."
Tung oil is marginally better, but still not ideal. Oil and oil/varnish
blends can't be built up on the surface of the wood because they
cure too soft.
I believe the Bichwood-Casey Tru-oil is a polymerized Tung oil, which is
very tough and durable. Polymerized finishes are difficult to use
on larger projects because they tend to dry too fast and are
expensive. Otherwise, polymerized finishes are very tough.
Read the label on the bottle carefully. Most of the time, the
manufacturer will call something an "oil" because of the feelings
of familiarity it causes. It may actually be something completely
different (such as a thin varnish suitable for wiping). The same
concept spills over to film finishes. Varnish and/or lacquer with
water cleanup ? Then they're not true vernishes/lacquers, but
a different animal altogether call water-base finishes.
If you have a wiping finish and you're not sure, pour some on
a piece of glass and let it cure. If it dries soft and wrinkly, it's
indeed an "oil" or oil/varnish blend. If it dries hard and (at least somewhat)
clear, it's something else, most likely a varnish. Most of the oil-
varnish blend and wiping varnish products have a name like
"Tung Oil Finish", or "Tung Oil Varnish". There's very few finishes
available which are pure boiled linseed or Tung oil. If you're going
to use a wiping varnish, you might as well use straight varnish,
because it will build up film thickness faster and yhou can save yourself
a lot of time.
2) A FILM finish is best, in particular tough finishes like Polyurethane. Film finishes
also include lacquer, and water-based finishes, but these are not as durable as
varnish or catalyzed film finishes (the latter is best, but you need access to spray
equipment. I like Sherwin Williams Water White Conversion Varnish). In particular,
I would recommend spray polyurethane to most people due to its ready availability and
easy of application.
As far as brushing polyurethane - actually, that is the preferred
methodon larger projects. The slow curing time of varnish
makes a really sticky mess of the overspray. One thing you
have to do when brushing a varnish is to level it and rub it
out. The steps are no different than the ones I listed, but take
more work since the sirface you start with is not as flat as when
you spray it.
In regards to varnish - varnish is created by heating a resin with
an oil to create a chmically new substance. Varnishes are
usually named based on the type of resin used: Polyurethane
and Alkyd are the most common. Spar varnish is used for
outside projects. It has a higher ratio of oil before being heated,
and makes for a more flexible film. This is a desired quality
for outdoor projects, as wood kept outside will still absorb
moisture to a greater degree and expand/contract more. If
the film weren't more flexible, it would crack. So spar varnish,
while you may believe it to be more protective, actually isn't.
Weird, huh ?
....continued in next post....