Here are some of my personal opinions for creating a quality, long-lasting
paint job:
If you sandblast your truck, I'd prime the parts immediately (before much flash
rust develops) with a good self-etching two-part (hardened) primer-sealer. OR,
I'd treat the bare metal with a metal-prep solution (using a simple
apply-then-rinse technique) and when dry, prime it with a non-etching two-part
hardened primer-sealer. Both approaches will give you a primer base that is
exceptionally well bonded to the metal and won't chip or flake off. It will
also help seal the metal against moisture and provide a good base for the
topcoat. Make sure that the primer is a primer-SEALER, or else you'll need an
additional sealer coat before painting.
Whatever you do, DO NOT use SANDING-type primers on bare metal. They don't bond
well to bare metal and will chip and flake easily!
Another tip. After priming, there is a 'window of opportunity' of a certain
number of hours during which you can paint the vehicle without having to sand
the primer. This varies with the primer you use. If you wait too long, all of
the volatiles will be gone and you'll have to lightly sand the surface (a
medium scotchbrite pad works pretty well) to make sure that the paint bonds
well to the primer.
Note that some people have a two-part primer-sealer tinted to match the desired
final color (such as olive drab) and actually make it double as the final coat
as well as the primer (possible military approach here?). I don't think I'd
recommend this, but as long as it's a primer-sealer and not just a primer, I
suppose you might get away with it.
After priming, I'd suggest using a two-part, catalyzed paint to provide better
sealing, more chip and scratch resistance, and probably better UV protection.
As to the type of paint to use for a top coat, you'll probably want to stick
with a two-part acrylic enamel...mostly because it's easier to work with and a
little cheaper than the urethanes and lacquers. Still VERY durable stuff. Plus,
if you want a semi-gloss (or flatter) luster, it's harder to achieve with a
urethane than with an enamel. Also, stick with one brand of paint throughout.
This all might sound kind of elaborate, but it really isn't. Basically, this is
just two coats: one primer-sealer coat and one final top coat (and possibly
preceded by some metal prep solution, depending on the primer you use).
By the way, if you haven't used catalyzed paints before, the "two-part"
business just means that you mix a hardener/catalyst with the primer or paint
before spraying. Most of these paints have a pretty long pot life...sometimes
as long as 36 hours...so you don't have to rush once you've mixed some up. The
only disadvantage to these two-part paints is their cost. Better paints just
cost more. Period. Spend the extra hundred bucks on the paint now and make it
last twice or three times as long.
Another suggestion: Get an HVLP gun to use with your compressor. You could
shell out for a turbine unit, but some of the newer gravity-feed type guns will
work with your existing compressor and don't require a particularly large
volume of air. Some can operate continuously with a 2 HP compressor. Check the
CFM and PSI requirement of the gun before buying it. You should be able to get
a good gun for about 175 US dollars. They can go a lot higher, but unless
you're doing regular production work and are working with difficult paints,
etc., it should do a good job for you. I've seen jobs done with 100-dollar guns
that look great...smooth, no orange peel, etc. It's really the operator...and a
clean, properly adjusted gun...and the proper consistency of paint...that make
the difference. Good lighting helps a lot, too. HVLP guns offer two important
advantages:
First, they use a LOT less paint. The transfer rate can be as high as 90% for
some guns...two to four times better than a conventional high-pressure gun.
Considering the price of good paint, the gun could pay for itself in ONE
vehicle paint job.
Second, they are better for the environment...and your lungs. Naturally, you
STILL want to wear an approved respirator when spraying or sanding any paint.
A note about rust: If you're painting over any existing rust, you obviously
want to seal it, but it's no more important to seal rust than it is to seal
bare metal. The main thing is that there is NO LOOSE rust (preferably no thick
deposits of rust that can flake off later), and that the primer-sealer that you
use is designed to bond well to a clean, solid rusted surface as well as to
bare metal. The self-etching primers or the metal-prep solution followed by a
non-self-etching primer should both work pretty well on a clean, solid, rusted
surface, even though the etching action is more pronounced on bare metal.
There are lots of "miracle" paints to use over existing rust. Some may be quite
good in their own way and I have no doubt that many of them do a good job in
sealing the metal and rust against moisture and oxygen. The question here is
their suitability as a primer coat...that is, how well subsequent layers of
paint will bond to them. I'm not going to make any recommendations here, except
that I personally would avoid the acrylic polymer types of rust killer
paints/solutions...at least for exposed areas. I think that chassis rails are
better candidates for these special paints than body panels. For rusted areas
on a chassis, after cleaning off the loose rust, you could use a good
slow-drying oil-base primer with talc, zinc phosphate/chromate, or silica.
These inert materials are designed to absorb the resins/oils and bond together
like overlapping bricks, sealing against air and water. The slower drying
primers have more time to penetrate existing rust, which tends to be a bit
porous. This approach seems to be similar to what Corroless describes.
Rustoleum rusty metal primer is an old standby that works pretty well. However,
as I said, I'd avoid these "special" rust paints on body panel surfaces. Stay
with the two-part hardened primers whenever possible on the visible sheet metal
areas.
Any metal that is properly sandblasted should provide a good paintable base for
your primer-sealer coat. Often, there are many tiny, pinpoint-sized rust specks
that just can't be sandblasted out without taking a bunch of good metal with
them. Don't worry about these. They won't hurt a thing. Just avoid leaving
larger areas of rust that could potentially flake off.
As usual, I've gotten a bit carried away. Anlyway, I hope that gives you some
material to work with. My final suggestion would be to talk with some
experienced painters with a good reputation. Of course, even if you do, you'll
get as many opinions as the number of painters you talk to. Still, they'll have
some good things to say.
Have fun,
Alan
(Salt Lake City, Utah)
RKiser8375@aol.com wrote:
> I have a question concerning repainting my M37. Apparently, the military did
>
> not use primer when they painted their vehicles. Mine appears to have bare
> metal underneath the OD #595-24087. Assuming I sandblasted the truck, is it
> necessary for me to prime it before I repaint it?
>
> Rob Kiser
> Bright Orange '52 M37
===
To unsubscribe from the mil-veh mailing list, send the single word
UNSUBSCRIBE in the body of a message to <mil-veh-request@skylee.com>.