COATING POLISHED BRASS

Q. We manufacture a line of decorative tubular railings and fittings. I was wondering if anybody had any ideas of what clear coating to put on polished brass, because we used a clear polyester topcoat on them and after three years, one of our customers complained about it developing what look like corrosion spots (I think caused by moisture) underneath the top coat.

I’m wondering if we should put a thicker coat or two coats of clear, or if there is any other product on the market that will just seal the brass so nothing can get to it.

The failed brass top rail sits on top of a railing in a greenhouse. We have been asked to refinish the railing.
If you have any ideas, please help. T.L.

 

A. I see three issues here: 1) Coating polished brass and its surface preparation, 2) Basic coating adhesion and 3) Continuous exposure to a humid atmosphere.

Coating polished brass with clears can be tricky. The brass must be squeaky clean. Even traces of oily soils, corrosion products, polishing compounds or other contaminants will cause adhesion and appearance failures in that location. Polyester coatings are rated as “good” for adhesion to polished metals.

On the other hand, epoxy/polyamides are rated as “excellent” for adhesion to polished metals. Furthermore, moisture resistance of epoxies is better than polyesters. Every greenhouse I’ve visited has been warm and humid, reminding me of the walk-in humidity chamber we had at work. You’ve sold your coated brass railing to a customer using it in a high-humidity chamber. That’s not a good thing.

My recommendation is: 1) Remove the old finish completely. 2) Re-polish the brass. 3) Remove all oily soils, polishing compounds and other contaminants. 4) Apply two coats of epoxy/polyamide clear finish.