From: "Barry L. Ornitz" <ornitz+U@dpnet.net>
Subject: Re: What paint to use on a tower
Date: 23 Apr 1999
Newsgroups: rec.radio.amateur.antenna

Famille Magnan wrote in message
<199904212050074965645@ppp2-201.infoteck.qc.ca>...
>I am in the process of taking a 68 feet tower down. There is surface
>rust on it. I'd like to know what kind of paint is best for this
>application. Also, what's the best way to get rid of the rust ? Sand
>blasting or with a grinder or sanding by hand ?


Different posters gave quite different responses, from Rustoleum to hot dip
galvanizing.  Gary Coffman gave the best answer - having the tower
professionally cleaned and hot dip galvanized.  This certainly offers the
best protection.  However it is relatively expensive for the small ham-type
towers commonly available.  But if you want to keep the tower for a long
time, and it is still structurally sound, the expense may be worth it.

The second best option (again if the tower has no structural damage) is to
use inorganic zinc coatings.  You will need to sandblast the tower first to
roughen the surface and remove all traces of rust.  The inorganic zinc is a
suspension of zinc powder in an ethyl silicate binder.  This chemically
reacts with both the steel and the zinc particles (forming insoluble metal
silicates) to give a good bond that is electrically conductive.  Testing by
power companies on a number of transmission line towers has shown this
coating is second only to hot dip galvanizing in its protection.  Several
companies make this coating material.  Porter Paints is the company that
immediately comes to mind.  This coating is expensive - about $75 per
gallon the last time I priced it.  Unlike regular paints, this material
prefers high humidity or moisture when it is applied.  However, it must be
coated with another paint after it cures.  The recommended top coat is a
polyurethane.  This coating has a very limited shelf life too.  It was used
extensively at Eastman Chemical Company to protect outdoor steel storage
vessels, pipe bridges, and buildings.

Someone else suggested the commercial cold galvanizing paints.  LPS and
others make these and they are commonly available.  These contain zinc
powder in an organic binder.  Unfortunately there is not much zinc.  The
coating is often barely conductive.  While it offers slightly better
protection than regular paint, it comes nowhere close to providing the
protection of the inorganic zinc coating.

Back in 1967, I used a zinc filled epoxy to paint a slightly rusted tower.
Unlike the cold galvanizing paints of today, this stuff was 75% zinc
powder.  A pint can weighed 4 pounds.  I wire-brushed the tower and used
this paint.  It was electrically conductive.  It protected the tower for
about 7 years before rust became a problem again.  This paint was made by
Devcon Epoxies and may still be available, but I would still suggest the
inorganic zinc coating instead.

Someone else suggested Rustoleum.  While this is commonly sold just about
everywhere, the results will be poor.  If, however, you plan to paint a
non-rusted galvanized tower, Rustoleum and other companies make paints and
primers that adhere well to the zinc.

To summarize this, consider the following table.  The best approach is at
the top (with cost no consideration).  The poorest approach is at the
bottom:

        1.    Hot Dip Galvanizing
        2.    Inorganic Zinc
        3.    Zinc-filled Epoxy
        4.    Cold Galvanizing Stray
        5.    Rustoleum
        6.    Regular House Paint

        73,  Barry L. Ornitz     WA4VZQ     ornitz@dpnet.net