Tractor Cab Coating

Q. I think I am looking at a failure of a powder coating on tractors I am considering purchasing. There is rusted sheet metal steel on these cabs. Do I go through the normal removal of rust to bare metal and repaint? I was thinking of removing loose rust using zinc-phosphate and then priming and painting with acrylic enamel.

The failures are on Jodale-Perry tractor cabs. This is the second failure I’ve noticed on this company’s products and I only  looked at these two units. One is a 1998 and the other is 2000 model cab. I am looking for enough information to allow me to consider fixing one of these units, and if it can be successful. All other aspects of the cab are of the highest detail, but the painting seems to be in question.  B.B.

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A. I was not familiar with the Jodale-Perry name, so looked them up on the Internet, and you are correct that they powder coat their products, although I am not aware what other steps (pre- or post-treatment) are part of their process. While the powder coating should provide reasonably good corrosion resistance, it will only be a good as its pretreatment. It is possible that some parts of the pretreatment were not performed correctly or an insufficient pretreatment was specified.

It was my understanding at one time that the pretreatment performed on “Class A” agricultural equipment is generally as good (and as involved) as that of the automotive industry. If that were the case, it would typically involve the use of double-sided electrogalvanized steel, a multi-stage pretreatment and zinc phosphate system, a cathodic, epoxy electrocoat primer, topcoat (typically solvent-based or high solids) with a final clearcoat. If the manufacturer simply applied a cleaning, iron-phosphate pretreatment, little or no priming and a single-step powder coating, and both of the cabs appear similar, it may be that is all the more you can expect from a pretreatment and coating such as that for the environment it is exposed to.

Regarding repainting: It is ideal to take all the rust off, get back to base metal, then apply the proper pretreatment (zinc phosphate is a good idea), prime and paint. If that is too difficult, there are some primers that allow you to coat rusted surfaces by “converting” it into a more stable base. However, I do not think that would be as good as taking it down to bare metal. Before purchasing a new cab, I’d investigate the current state of the supplier’s pretreatment and painting process. It could be that it has improved over time.