PAINTING GALVANIZED TANK

 Q. I have a 750–1000 gal galvanized holding tank used for maple syrup production. The tank has not been used for a number of years and has some surface rust. I would like to remove the rust and coat the inside of the tank to be able to use it again to store clear water, which will be used in our Reverse Osmosis machine. Because of the use and need for it to be food safe I am unsure of what to use to coat/paint it. Any ideas? M.F.

Any advice is appreciated. Also, if you have another recommended paint application method besides electrostatic, I’d be willing to entertain that too. My biggest concern is getting good DFT on the surfaces inside of the holes. B.T.

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A.Many years ago, I was involved in a project to develop a coating for the inside surfaces of aluminum beer kegs to be used in home refrigerators. I shake every time I think of it, and not because the beer was cold. As you already know, the FDA requires that any coating coming in contact with food have their approval. Furthermore, all the constituents of the coating must have their approval. With this in mind, I am reluctant to make, and owing to the policy of Painting Clinic, I cannot make specific recommendations.

I can tell you that any surface rust must be removed before painting. If the rust removal process involves the use of wire brushes or steel wool fresh zinc may be exposed. One of the problems associated with painting galvanized surfaces is the reaction of certain resins with the zinc. To passivate the zinc, zinc phosphate and chromate pretreatments can be applied to the surface before painting or a finish system specially formulated for use on zinc surfaces can be used. For example, systems using vinyl wash primers and zinc-rich primers, without pretreatment, are used successfully on galvanized surfaces.

To save you time, I suggest you contact a paint supplier who has FDA-approved products. Explain your problem completely to him. Obtain and follow his surface preparation recommendations and apply the product according to his instructions. Your suppliers or customers may be able to identify such a paint supplier.