I'd recommend that anyone who is contemplating re-doing the
sound-proofing on their car consider a few things first: Regardless of
whether or not you intend to put down a new bitumastic cut-out
deadener or add just a layer of the padded type, I suggest that you
strip the floor-pans down to bare metal, etch/abrade out all the old
rust (don't worry, even if the paint looks good, you'll find some rust
there, lurking, waiting, around the drain holes and the captive nuts
for the seats if nowhere else), and use one of the following three
primer/sealer products (or something of a similar chemistry, if you
understand how these three work): Rust Bullet, Master Series Silver or
Eastwood's Rust Encapsulator. The first two are essentialy identical:
Moisture-cured urethanes with aluminum powder as the pigment (I've
even heard rumors that they are made by the same factory, and just
receive different labels). Rust Encapsulator has a different
chemistry, but all three work much better than POR-15, as confirmed by
independant testing.
The reason I recommend this laborious process is for the following
reasons: When the factory 'tar' soundproofing is pulled up, it often
takes some top coat and primer with it. Most of us use a scraper and
heat-gun to pull it up. The scraper is bound to penetrate the
paint/primer somewhere, and the heat gun is bound to loosen the
paint-bond somewhere, after all, what else are pain-guns used for????
While the factory primer on the 70's models is pretty tough, it
doesn't stop undercutting of rust even if you don't pull it up with
the 'tar'. Many times I've stripped away perfectly good looking
factory primer to find alot of pristine metal criss-crossed with the
tin-worm, making the panel in question look like a road-map. Also,
many of these cars have been restored with laquer-based paints, which
stop moisture penetration about as good as Iraqi border police stop
insurgents from entering the country. Also, if you are adding one of
the cheaper padded sound proofing materials (also intended as thermal
insulation) atop the factory stuff, they can hold moisture like a
sponge. By the way, some of the cheaper ones ARE made from shredded
scrap cotton sprayed with fire-retardant and backed with a cheap foil
that will rip if you sneeze. While I was cutting some of that stuff
(from J.C. Whitney, perhaps, or Vicky Brit), I actualy found a t-shirt
label in the mix! Anyhow, none of us want to have to replace our
floor pans after just a few years, so I highly recommend the extra
labor now, even if your floor looks good. At the very least, I'd
suggest scuffing the current paint with 150-grit and then covering
with one of the three products, as they will form a better barrier
than anything wlse I've come across.
Two coats of any of these essentialy seal the metal for good.
Moisture-cured urethanes stick much better than epoxies (made the
mistake of getting some on my hands two weeks before my wedding, and
it took hours of scrubbing with pumice the night before to get rid of
my epidermis, as the paint wasn't leaving on it's own) and tend to be
far more flexible as well as resistent to chemicals and acids. I've
beome very familiar with the Master Series product, as I live in a
very humid environment, and have no idea how long my car is going to
be un-painted while I make all the body-mods. So I strip a portion of
the car and do chemical or mechanical rust removal, and then hit the
area with the product, followed by a second coat the next day. When I
strip an adjacent area, the best paint removers do almost nothing to
the Silver primer, and when I use acid for the rust, it also does
nothing to the Silver primer (sometimes turns it a bit yellow). None
of the epoxies I've used even come close!!! The only problem I've
encountered is that it looks about the same color as the stripped
steel, so I have missed the occassional spot (I use a foam roller and
brush for this paint, as I'll be block sanding later, which will
remove any stipple). The bare spot will show up a few weeks later
with rust, but it won't undercut the primed areas. Then I just fix
these spots. If you are working on your car piece-meal like me, I
can't think of a better product. It was developed for priming
bridges, with minimal rust preparation, and this is an inherantly
corrosive enviroment, where the tests show it lasts over a decade.
I've only used the Eastwood Rust Encapsulator a little bit, but I've
seen a few independant tests that rate it quite highly.
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