Powder Coating Q&A: Proper Coating for a Public Restroom

Q. I am developing a product made of aluminum 6061 that will be anchored to the floor of public restrooms, so the foot will be splashed by a detergent-filled mop as many as 20 times a day. I’m getting contradictory advice from potential suppliers and shops. Some say that I needn’t worry too much while others say “better safe than sorry” and recommend epoxy, or a second coating.

In the end, everyone seems to agree that I should first try the cost efficient solution of polyester, and see if it holds. Everyone also agrees that the texture of the finish (glossy, rough, fine textured) doesn’t really matter. What do you think?

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A. Tricky business, trying to predict what will happen to a coating layer in the field. Here are my thoughts: Anything that is fastened to the floor is subject to physical abuse. It starts with the installation when a person with tools puts it in place and then fastens it to the floor. Then there are the mops, buckets and other things that may cause chips or scratches in the film. Your coating needs exceptional mechanical properties.

Next, there is the added stress of corrosives. In spite of what some will say about detergent, water and detergent can do a lot of damage over time. If the film has thin spots or breaks in the coating, the detergent and water mixture will eventually find their way to the aluminum under the coating. If the aluminum has been treated with a chromate or quality non-chrome aluminum conversion coating, it may survive spot exposure to moisture. But some gradual break down is expected if the coating layer is too thin.

If the aluminum is blasted or processed only through an iron phosphate washer, it is a matter of time before the entire surface fails. Keep in mind, the exposure to the cleaning solution leaves a wet surface around the parameter of the base.

So, what should you do? Limit sharp edges in your design. That is the first place that break-down can occur. Rounding edges and corners within practical limitations will improve your edge coverage and help avoid failure. You need to have one of two things: a very good aluminum conversion coating or a layer of epoxy primer. A double layer of powder (primer plus topcoat) is probably the most certain solution. A single coat of polyester without a chrome, non-chrome or very good zirconium oxide coating is certain to fail. If it was my product and long-term corrosion resistance and adhesion were critical, I would use a non-chrome aluminum conversion coating, a layer of epoxy primer and a topcoat of TGIC polyester.

Originally published in the February 2016 issue.