There are paints that don't need primers to go on over rust (just remove
heavy flaky rust not light rust.) Rustoleum is one brand with such
products. I have used a lot of their "Hammertone" paint made to go on over
rust with no primer. I painted some rusty square steel tubing used as
columns to support my back porch slab above the walk-out basement's patio,
an area exposed to full sun, rain,ice and snow. That was 10 years ago and
there is no sign of rust, plus the paint looks near new. I buy it at Lowes
in quarts and spray cans. Comes in black and silver (special bulk buys
allow buying other colors.) I had them tint some silver as dark green as
they could and got a lovely shade of light green.
Patrick NJ5G
-----Original Message-----
From: Donald Chester
Sent: Friday, November 28, 2014 10:54 PM
To: towertalk@contesting.com
Subject: [TowerTalk] Aluminium Paint versus Cold Galv
Reviewing the archives, I see many posts over the years on the subject Cold
Galvanising paint. Some say it works wonders while others have reported it
being no better than ordinary paint. Here is my experience.
I once used a spray can of Cold Galv on another outdoor steel structure, and
recall rust spots creeping through within just a few months. I have used
aluminium paint on unprotected steel, and on galvanised steel showing signs
of rust, and it always seems to last a long time before more rust appears.
The steel casting on the salvaged broadcast station base insulator I use
with my tower was not galvanised at the factory. After erecting the tower I
painted the ungalvanised casting with aluminium paint, and in the 33 years
that I have had the tower up, I have re-painted it only once. Aluminium
paint seems to be almost as good as hot-dip galvanising for warding off
rust, and I believe it is a more effective product than Cold Galv for
protecting steel.
Here is a brochure from ALCOA touting the advantages of aluminium paint.
See
https://ia601502.us.archive.org/33/items/AluminumPaintATreatiseOnThePhysicalPropertiesOfAluminumPaintAndIts/AluminumCoOfAmericaCca39891.pdf
According to the brochure, "Many power companies are finding aluminium paint
more satisfactory than galvavizing for protecting the steel towers used in
supporting power lines... In painting towers, bridges and structures in
general, the painter appreciates the difference in weight... Since the
corrosion of iron and steel is caused by moisture and oxygen, it is obvious
that a highly impermeable paint film is desirable for their protection"
ALCOA goes on to say, "The metallic aluminium flakes, called aluminium
bronze powder, which are its pigment portion, have many unique and useful
properties which no other paint pigment has. The simple mixing of this
aluminium bronze powder with a suitable oil or varnish vehicle at once
provides an aluminium paint which renders unusually satisfactory service in
many and varied applications... Aluminium bronze powder for paints is made
by stamping aluminium into very small and thin flakes... The shape of the
particles of aluminium bronze powder is of particular interest. The ordinary
pigment materials like zinc oxide, red lead, white lead, etc., are composed
of particles distinctly granular in form even though they be exceedingly
small. Aluminium bronze powder is, however, essentially flake-like in
character... little particles of aluminium swirl about in the liquid and
many of them come to the surface of the liquid and remain there... Very
quickly an almost continuous film of metallic aluminium is formed at the
surface of the varnish by the little flakes... which arrange themselves, in
layer upon layer, much like fish scales... descriptively called LEAFING..."
Of course, one must keep in mind that ALCOA is promoting their product, but
still this is a credible explanation. Cold Galv uses tiny particles of zinc
suspended in the vehicle/bonding agent of the paint to coat the steel, on
the theory that the zinc particles will protect the steel in the same manner
as the solid layer of zinc in real galvanising. But with hot-dip
galvanising, the zinc coating is directly bonded to the steel like solder,
making electrical contact with the steel substrate. By galvanic action
(hence the term "galvanising"), the zinc sacrifices itself in the presence
of corrosive substances like sulphuric acid in polluted air, thus protecting
the steel from rust. With zinc paint, the particles are suspended in the
varnish-like vehicle of the paint, which continues to serve as a bonding
agent after the paint dries. Since varnish is an electrical insulator, not a
conductor, each zinc particle is effectively isolated from the steel it is
supposed to protect, so how could any galvanic action occur?
Don k4kyv
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