Towertalk
[Top] [All Lists]

[TowerTalk] Aluminium Paint versus Cold Galv

To: "towertalk@contesting.com" <towertalk@contesting.com>
Subject: [TowerTalk] Aluminium Paint versus Cold Galv
From: Donald Chester <k4kyv@hotmail.com>
Date: Sat, 29 Nov 2014 04:54:48 +0000
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
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
                                          
_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk

<Prev in Thread] Current Thread [Next in Thread>