As stated in the 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 AISC Specification Commentary Section M3.1, "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.  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.

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 AISC National Engineering Conference, Milwaukee, WI, AISC, Chicago, IL.

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Technical Advisory

Anecdotal evidence suggests a recent increase in the specification of primer for fully enclosed steel members in building structures. However, this practice is not recommended and unnecessarily results in increased costs while also producing a negative environmental impact. Click here to view the full AISC Technical Advisory.

When paint is required, SSPC emphasizes the importance of the development of a total paint system. Among the primary considerations for this design decision by the owner, architect, or engineer are: 

1. The end use of the member. 
2. A realistic estimate of time and severity of exposure of each coat of paint. 
3. An economic evaluation of the initial cost as compared to future maintenance cost. 
4. A practical determination of the division between shop and field work and responsibilities.

last modified 18 September 2002

The following information should be specified when steel is to be painted: 

1. The type and manufacturer of the specified paint (one alternative is the fabricator’s standard shop primer) 
2. The required level of surface preparation (expressed as an SSPC designation, i.e., SP2) 
3. The desired dry film thickness of each coat 

All technical data and directions for application of the specified paint, including required curing time, will be obtained by the fabricator from the paint manufacturer and need not be repeated in the contract documents, other than by reference.

last modified 1 January 2006

When contract documents call for a "shop coat" or "paint" without specific identification of a paint system, this is interpreted as the fabricator’s standard primer applied to a minimum thickness of 1 mil on steel that has been prepared in accordance with SSPC-SP2, with no conditional performance implied.

last modified 18 September 2002