[TowerTalk] Aluminium Paint versus Cold Galv

[Patrick Greenlee]

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 at 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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