Can Galvanized Steel Be Painted?
Q. I was wondering if it would be possible to paint some galvanized steel beams and extrusions I have with any kind of paint. And if so, would the paint last, and would it ruin the galvanized finish?Rick Navarro
- Anaheim, California
A. Galvanized material can be easily painted successfully. Surface preparation is the key. You need to ask the paint manufacturer if your paint is suitable for a top coat for galvanized material and what the proper surface preparation should be. The paint will enhance the galvanized coating. It will act as a barrier protection for the galvanized material and subsequently the galvanized material will allow the paint to last longer because there is no underlying corrosion. Painting over galvanizing is often referred to as a "duplex coating." It is routinely done for street lights, DOT applications, and various architectural applications.Mike Stroia
- Canton, Ohio
A. Yes, Rick, it is done routinely, but among other things galvanized finishes that are not going to be painted are chromated, whereas galvanized finishes that are to be painted are not. Painting a chromated galvanized finish is not done as easily -- but any galvanized finish can be painted. The American Galvanizers Association has several free on-line brochures.
Although URLs break or change over time, in May 2013, the following URL led to an excellent 12-page booklet called "Duplex Systems"
Ted Mooney, P.E. RET
Pine Beach, New Jersey
I need to know if by any means can we paint on 11 Gauge Galvanized Steel? If yes, then what is requirement for surface preparation and all other information.
Thanks in advance.
designer - Ajax, Ontario, Canada
A. This is a tough question to answer without full context, Purnendu . . . because an individual consumer may be perfectly satisfied with a do-it-yourself paint job, but might find the same quality on an OEM part to be unsatisfactory.
When a consumer is trying to paint existing galvanized steel it may be hard to get good adhesion, but scrubbing with trisodium phosphate and a tampico brush, followed by a self-etching primer made for galvanized steel may be good enough.
But when an OEM wants to paint galvanized steel, it starts with specifying the galvanized steel. Ideally it will be galvanneal, as used on auto bodies. If not, at least the final chromate treatment should be omitted. Then a conventional phosphatizing treatment at the factory. ASTM D6386 [link by ed. to spec at TechStreet] specifies the "Standard Practice for Preparation of Zinc (Hot-Dip Galvanized) Coated Iron and Steel Product and Hardware Surfaces for Painting".
The American Galvanizing Association calls galvanizing followed by painting a "duplex coating" as Mike has advised, and they have several booklets with full details at www.galvanizeit.org. Good luck!
Latex Self-Etching Primer
February 12, 2009
Q. Hello. I am the Materials Manager for a metal stampings organization currently stamping and welding a galvanized steel commercial washing machine console. We are currently sending this part out after stamp and weld to a subcontractor to paint. Throughout the 1.5 years this has been in production we will get random spikes in fallout from our paint supplier in the range of 90-100%. They are blaming the galvanizing and/or "outgassing". The material used is at this spec: "HOT DIPPED GALV G90 CS EXTRA SMOOTH, NON CHEM TREAT COATING PER ASTM A653 [link by ed. to spec at TechStreet] ZERO SPANGLE - EXTRA SMOOTH FINISH". The issue is what appears to be dirt / trash in the paint. What are possible causes of this? Is there a very specific pretreatment that should be required to E-coat/paint this type of steel? Thanks!Eric Baker
- Louisville, Kentucky