Q. I run a commercial painting contractor business. A customer wants us to paint the underside of galvanized steel metal decking, which happens to be the interior ceiling of his new structure. The metal has been up for seven months, and he decided he wants it painted white to brighten-up the factory. I was planning on cleaning the ceiling with vinegar and then painting it. Incidentally, the rest of the building is not completed yet so it is essentially empty. Do you have any other suggestions for painting it? B.H.
A. Painting is the easy part; the hard part is surface preparation. Wiping with vinegar will passivate a galvanized steel surface, however that’s not the difficulty here. Wiping a ceiling probably will not allow the vinegar sufficient reaction time to passivate it.
Another approach is to wash the surface with a hot detergent solution to remove any oily soils and then paint using a special primer for galvanized steel. Most often an oily or waxy substance is applied to galvanized steel at the mill to prevent white corrosion. Detergent washing also will remove finger grease.
The surface must then be thoroughly rinsed with water to remove the detergent. This process would involve power washing with a hot detergent solution and then rinsing with clear water. The difficult part of this approach is working overhead. An alternative to power washing is hand wiping, which may not effectively remove all the oily soils.
Your paint supplier will have a primer for galvanized steel. Buy that and apply it according to the manufacturer’s directions. If it is white, one coat should be sufficient. If not, it can be topcoated using any white paint
Power washing probably requires the workers to wear goggles, protective clothing and other devices to comply with OHSA regulations. The paint can be applied using rollers.