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Your Host and Tour Guide:
Paul Oman, MS, MBA - - Progressive Epoxy Polymers, Inc. - -
Member: NACE (National Assoc. of Corrosion Engineers), SSPC (Soc. of Protective Coatings)
"Professionals helping Professionals"
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How Zinc Primers Work
Zinc rich primers are used to protect steel surfaces from corrosion. Unlike regular paints or epoxies which resist
corrosion by forming an impermeable barrier between the metal and atmospheric moisture, zinc rich primers provide
corrosion protection by electrical means. The zinc and the steel for a tiny electrical - cathodic cell that protects
the steel at the expense of the zinc. Of course the zinc primer also provides a little barrier' protection as
well.
Why Use Them
Some types of zinc rich primers (inorganic - see below) are used as a stand alone coating, but often they are topcoated
with a paint or epoxy (many industrial coating specifications call for a zinc primer, epoxy intermediate coat and
a urethane topcoat - we offer such a system as well - CLICK HERE for more information). A zinc primer under a topcoat
of epoxy or urethane paint provides a backup or secondary method of protecting the steel from corrosion.. Although
epoxies can, and often are, used successfully on steel surfaces without any sort of general purpose primer or zinc
primer..
Organic vs. Inorganic Zinc Primers
There are two types of zinc primers, organic and inorganic. Generally inorganic primers must be spray applied.
They do not have to be topcoated and provide better steel protection than non-topcoated organic zinc primers.
Organic zinc primers (often zinc in an epoxy) can generally be applied by brush, roller or spray. If not topcoated
they do not protect the steel as well as an inorganic primer, but tests show they do offer the same degree of protection
if the primers are topcoated.
A new flavor of organic zinc primer is a moisture cured urethane zinc primer. Moisture cured urethane (MCU) coatings
are easier to apply and work with than epoxy based organic zinc primers and are one component (one pack) products,
not counting the zinc powder which must be added into the epoxy or MCU. Pricing of organic and inorganic zinc primers
are all similar. The zinc rich primer we offer is a moisture cured urethane.
Our Recommendation for Coating Steel Surfaces.
Perhaps the best system for coating steel is as follows:
1) Abrasive blast new steel. Old steel should be abrasive blasted or waterjetted down to white' metal. The initial
abrasive blast gives a metal a surface profile which is very important for a good coating bond.
2) Treat with a soluble/insoluble salt remover. (We do not carry this kind of product). This is becoming more recognized
as an important pre-coating step.
3) A zinc rich primer. (Probably an organic zinc primer - moisture cured - if applied on site or an inorganic zinc
primer if applied in a shop where conditions can be better controlled). We do not carry/sell zinc primers. WE DO
NOT CARRY OR RECOMMEND ANY PARTICULAR ZINC RICH PRIMER
4) A solvent based (greater than 0% VOC) epoxy intermediate coat with a urethane topcoat, or a 100% solids (0%
VOC) epoxy topcoat without the urethane. Note: we offer an intermediate epoxy coat - 18% VOC - and a excellent
two-part acrylic polyurethane topcoat.
NOTE: If I were to omit any of the above steps, it would be the zinc rich primer. The zinc primer certainly is
beneficial, but the other steps are more important and modern epoxies do provide outstanding protection of steel
when used alone and without any sort of primer.
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