Touch-up & Repair
Although galvanized coatings are highly
abrasion resistant, coating damage may occur
once the galvanized steel leaves the
galvanizer's facility due to extremely rough
handling, installation techniques, or
in-service conditions. There are methods
available to ensure post-galvanizing coating
integrity.
There are three widely available accepted
touch-up and repair methods: zinc-rich
paint, zinc-based solder, and zinc flame
spray (metallizing).
Zinc-rich paint
Organic or inorganic zinc-rich paint for
touching up and/or repairing galvanized
steel should contain between 65-69% zinc by
weight, or >92% by weight metallic zinc in
dry film. Inorganic zinc-rich paints are
more effective than organic in terms of
delivering corrosion protection, and they do
not shrink after drying/curing as organic
coatings do. This is a major advantage when
the paint is applied to corners, edges and
rough surfaces.
Zinc-rich paint is brush-
or spray-applied to a clean, dry steel
surface. Spraying or brushing should be in a
single application of multiple passes
according to the paint manufacturer's
instructions. Zinc painting can be done on
the job-site and is the easiest repair
method to perform because limited equipment
is required.
Zinc-based Solder
Soldering with zinc-based alloys consists of
applying zinc alloy -in stick or powder form
-to the area to be repaired, which has been
preheated to approximately 600 F (315 C).
Common repair solders include zinc-tin-lead,
zinc-cadmium and zinc-tin-copper alloys.
the surface to be reconditioned shall be
wire-brushed, lightly ground, or mild
blast-cleaned. All weld flux and spatter
must be removed by mechanical methods if
wire brushing or light abrasive-blasting is
inadequate. The cleaned area should be
preheated to 600 F (315 C) and wire-brushed
at the same time. Care must be taken to not
burn the surrounding galvanized coating.
When the repair has been completed, flux
residue can be removed by water rinsing or
wiping with a damp cloth.
Zinc Flame
Spray (Metallizing)
Metallizing is the
melting of zinc powder or zinc wire in a
flame or electric arc and projecting the
molten zinc droplets by air or gas onto the
surface to be coated. The zinc used is
nominally 99.5% pure or better. The
performance of wire versus powder is
comparable. Zinc-aluminum alloys also can be
used. The application equipment used may
limit the concentration of aluminum.
