Richard mentions, “Because the steel did not exhibit the color of the specified primer, we were able to prove it was never primed…” That’s one good reason to specify a particular color.
One of Tnemec’s popular primers is available not only in “iron oxide” red, but also, I believe, in green and gray. I have often wondered if red primers were meant to disguise rust, while other colors were intended to make it more evident…
The following was copied from the AISC web site.
10.1.1. When must structural steel be painted?
As stated in the 2005 AISC Specification Section M3.1, “Shop paint is not required unless specified by the contract documents.” Therefore, fabricated structural steel is left unpainted unless painting requirements are outlined in the contract documents.
In building structures, steel need not be primed or painted if it will be enclosed by building finish, coated with a contact-type fireproofing, or in contact with concrete. When enclosed, the steel is trapped in a controlled environment and the products required for corrosion are quickly exhausted. As indicated in the 2005 AISC Specification Commentary Section M3.1, “The surface condition of steel framing disclosed by the demolition of long-standing buildings has been found to be unchanged from the time of its erection, except at isolated spots where leakage may have occurred. Even in the presence of leakage, the shop [primer] coat is of minor influence (see page 391 Bigos, Smith, Ball, and Foehl, 1954)1.” 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.
In exterior exposed applications, steel must be protected from corrosion by painting or other means. Likewise, steel must be protected from corrosion in special applications such as the corrosive environment of a paper processing plant or a structure with oceanfront exposure.
[1] Bigos, J., G.W. Smith, E.F. Ball, and P.J. Foehl, 1954, “Shop Paint and Painting Practice,” Proceedings of the 1954 AISC National Engineering Conference, AISC, Chicago, IL.
last modified 1 January 2006