Scene 1
A rusted control arm or coil spring or push rod rests on a table in your
garage. The part's been there for months waiting to be restored. You intend to
sandblast it and paint it with two coats of
POR-15® Clear Rust Preventive Paint. You
want the look of bare, clean metal through the glossy coating. You are an
experienced restorer.
Scene 2
Your buddy has sandblasting equipment. You blast your control arm or
springs or whatever, wrap it in newspaper or brown Kraft paper and take it back to
your garage, making sure you don't touch it with your bare hands. The weather is
sunny, or overcast, or rainy, or you choose it.
You open your can of POR-15 Clear and lay down a thin, covering coat. The
part looks gorgeous. Four hours later, or the next morning, you put down your
second coat. Looks great.
Scene 3
A week later or two weeks later you examine the part and see a
rust-colored spot or two under the coating, which still looks otherwise perfect. What's
going on here? This stuff is supposed to stop rust. Have I done something wrong?
Here's What Happened
Now let's go back to the beginning where the rusty control arm is resting on
your bench. It's been indoors for months, so it must be dry, right? WRONG!!
Ordinary steel is very porous. That control arm has thousands or millions of
microscopic cavities in it that are filled with moisture. Even after sandblasting, thousands
of moisture pockets remain. The piece may look dry, but it isn't... and if you let it sit
in your garage after blasting for a few hours before you paint it or worse,
overnight, more moisture settles in to haunt you later. POR-15 is hydrophilic
(moisture-seeking). The first coat 'pulled' that residual moisture to the surface and sealed it
in, as did the second coat. Microscopic corrosion then occurred under the coating
and became visible to the naked eye. The POR-15 coating did not break because
it's flexible and very tough, but if enough moisture remains under the coating and
the corrosion continues for a while, that may occur in the future.
Get The Moisture Out First
After you've prepared your part for painting (by sandblasting,
metal-prepping. etc.), use a warm air blower to make sure the piece is bone-dry, then paint it at
once.
Apply your second coat or POR-15 when the first coat is just dry to
the touch with slight finger-drag remaining. And never forget
the three most important rules of painting:
