CHICAGO – Anecdotal evidence suggests that specifiers are increasingly requiring that fully enclosed steel members in building structures be primed.
The American Institute of Steel Construction has issued a technical advisory to clarify the matter.
For almost 70 years, AISC has recommended against painting or priming steel that will be enclosed by building finish, coated with a contact-type fire-proofing, or in contact with concrete. Doing so results in unnecessary costs and delays as well as negative environmental impacts.
Section M3.1 of the AISC Specification for Structural Steel Buildings (1993, 1999, 2005, 2010, 2016, and 2022) indicates that shop paint is not required unless specified in the contract documents. “The surface condition of unpainted steel framing of long-standing buildings that have been demolished has been found to be unchanged from the time of its erection, except at isolated spots where leakage may have occurred,” the Specification’s commentary notes. “Even in the presence of leakage, the shop coat is of minor influence (Bigos et al., 1954).”
A similar situation exists when steel is fireproofed or in contact with concrete; in fact, paint is best omitted when steel is to be fireproofed because primer decreases its adhesion.
There are, of course, exceptions. AISC recommends painting or priming enclosed structures when the expected relative humidity level is above 70% as well as in industrial structures where the steel will be exposed to corroding chemicals.