Letter 40001

Improving adhesion of TGIC powder over hot dip galvanized steel  

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Is there any products that would improve the adhesion of our powdercoating over newly hot-dip galvanized steel that does not have major environmental issues or require the use of an automated 5 stage wash system?

We are a manufacturer of steel products in Phoenix, Arizona. Our products are used in the Phoenix area only and normally we do not have issues with serious rust issues since our climate is very dry. Our powder coating is done in house and is a simple batch booth and oven. Our cleaning process is simple. After cutting, all components are hand washed with a degreaser/cleaner. After fabrication and before powder coating we use a manual power washer to clean off any soot from the welds. This has worked very well in Phoenix and the rust that we do get is surface rusting from scratches to the finish.

We have been interested in offering our product nationally, however, as we currently finish our product, I would not want to offer it as is. We have been researching hot-dip galvanize after our fabrication is done and then powder coating. We have done some test with our TGIC powder over freshly galvanized product and mostly it has been very good but we have noticed a few failures in adhesion. Our galvanizer recommends a zinc phosphate pretreatment, but we worry about the environmental issues and the necessary equipment. One powder supplier recommended Picklex but after talking to the company, I feel it is too expensive since the manufacture told me I could not dilute it.

Scott Guthrie
fence company - Phoenix, AZ USA

Hi Scott,

You are getting good advice from your galvanizer. If your products are going to be offered nationally, then they will see many environments that are more corrosive than the climate in Phoenix.

Zinc phosphating is the pretreatment of choice for galvanized surfaces, but you might be successful with an iron phosphate system that utilizes a high-performing final rinse. If you are using a high-quality powder coating, all the better.

George Gorecki
- Naperville, Illinois