Primed steel in concealed construction?

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Author Message David Axt, AIA, CCS, CSI Senior Member Username: david_axt Post Number: 569 Registered: 03-2002 Posted on Tuesday, November 01, 2005 - 01:19 pm:    There is a debate in our office. Should structural steel be primed even though it is concealed and will not be fireproofed or painted? Why or why not? Richard L Matteo, AIA, CSI, CCS Senior Member Username: rlmat Post Number: 122 Registered: 10-2003 Posted on Tuesday, November 01, 2005 - 01:32 pm:    In a previous firm, we always primed the concealed steel as it sometimes sat in the fabricator's yard or at the job site for a while before being installed and it will rust. We also called for it to be touched up in the field after installation to prevent rusting after it was concealed. Shop prep included SP-6 and a zinc-rich primer and field touch consisted of SP-3 prep and same zinc-rich primer. I still specify it in my current firm. This tends to be the optimum, so if cost is an issue, the standard primer may suffice, provided it is something like Tnemec 10-1009 or similar and not what the fabricator happens to have laying around in his shop. A lot depends on where the fabrication shop is and how soon the material is installed after delivery. J. Peter Jordan Senior Member Username: jpjordan Post Number: 150 Registered: 05-2004 Posted on Tuesday, November 01, 2005 - 02:31 pm:    I should think it has a lot to do with the environmental conditions of the fabrication and construction site. I am not sure that I would recommend primer for a project in Phoenix, but I would definitely consider going beyond the standard for a project in Galveston. I looked at a project in an urban area several years ago; a multi-story open garage with a structural steel frame completed 3 years earlier. The Owner had deleted the painting from the contract which had evidently included field touch-up of primed surfaces damaged by handling or connecting/welding. The primer (a "stock" inexpensive shop primer) had held up very well except where it had been damaged. There was some degredation with the most severe exposure along one side of the structure. I concluded that had the Owner gone ahead with touching-up the primer, field painting could have been delayed a little longer. In a few cases, corrosion at bolted connections and welds was severe enough to be more than a little scary. I know the inside is "air conditioned," but it doesn't start out that way and concealed areas will not be ventilated. In more hostile areas, how lucky do you feel if you omit the primer? Richard L Matteo, AIA, CSI, CCS Senior Member Username: rlmat Post Number: 123 Registered: 10-2003 Posted on Tuesday, November 01, 2005 - 02:39 pm:    I agree with Peter. The project that prompted my former firm to go with the upgraded primer had steel arriving at the job site already rusting. It turned out that the fabricator's storage yard was located on the Brooklyn (NY) docks!! Here in California I call for the higher grade when the project is near the ocean or in higher elevations where it snows. Anne Whitacre, CCS CSI Senior Member Username: awhitacre Post Number: 264 Registered: 07-2002 Posted on Tuesday, November 01, 2005 - 04:50 pm:    David: does your structural consultant have an opinion? our stuff is always shop primed, precisely for the conditions stated above: it sits around the job site, is exposed (often to salt air) for some period before building enclosure; and if nothing else, is shipped on some large vessel from Korea and is exposed to salt air and unconditioned space just to get to the job site. Doug Brinley AIA CSI CDT CCS Senior Member Username: dbrinley Post Number: 143 Registered: 12-2002 Posted on Tuesday, November 01, 2005 - 04:56 pm:    "Structural steel that is not indicated to be painted or 'fireproofed' should be prime-painted with one (1) coat of the fabricator's standard rust-inhibitive primer." David Axt, AIA, CCS, CSI Senior Member Username: david_axt Post Number: 570 Registered: 03-2002 Posted on Tuesday, November 01, 2005 - 05:35 pm:    Actually how this question came about is that the structural engineer put the note, "Structural steel shall be unprimed unless otherwise noted." in the structural general notes. We did not indicated what pieces of steel were primed but we did indicated the type of primer in the specs. So ALL the structural steel arrives on the jobsite unprimed. AISC says that it is okay for bare steel to be in enclosed concealed construction. (Unregistered Guest) Unregistered guest Posted on Tuesday, November 01, 2005 - 06:41 pm:    David, Is it a school project? David Axt, AIA, CCS, CSI Senior Member Username: david_axt Post Number: 571 Registered: 03-2002 Posted on Tuesday, November 01, 2005 - 07:34 pm:    Yes it is a school project in the Puget Sound area. The contractor was extra money for something he should have provided in the first place. He is notorious for "dialing for dollars" on our projects. Doug Brinley AIA CSI CDT CCS Senior Member Username: dbrinley Post Number: 144 Registered: 12-2002 Posted on Tuesday, November 01, 2005 - 07:47 pm:    GC/CM or design/bid/build? Mark Gilligan SE, CSI Senior Member Username: markgilligan Post Number: 44 Registered: 05-2005 Posted on Wednesday, November 02, 2005 - 01:14 am:    The practice of applying a shop coat of paint to all structural steel is un-necessary, un-economical, and can cause problems. The rust that occurs prior to the structure being enclosed may look bad but it is not an issue structurally. There might be situations where the steel is stored a long time in a corrosive atmosphere but in today’s fast tracked projects that is typically not an issue. In addition if the corrosion prior to enclosing the structure is significant you should be able to reject the steel. The question is can you justify the added expense for a low likelihood event. Furthermore the shop coat by itself is not adequate to deal with corrosion issues. If you have an expectation of moisture problems you need to do something more than just a shop coat. The reality is that most modern large steel buildings do not have a shop coat applied and there have not been significant problems. A shop coat should only be applied when a subsequent finish will be applied either for aesthetic or corrosion protection. If this is the case you need to coordination of the shop coat with the finish treatments. This coordination is often overlooked. The existence of a shop coat on steel that will be encased in fireproofing will typically cause problems with the adherence of sprayed on fire proofing. You can still apply sprayed on fireproofing over painted steel but you need to either use special paints or you need to attach wire mesh to the steel to hold the fireproofing in place. This may be necessary when there are corrosion issues since the sprayed on fireproofing does not provide corrosion protection. The wrong type of shop paint can also cause a safety problem for steel erectors so be careful that you do not specify a paint that causes the iron workers to slip. Even when shop coat is applied it is omitted where steel is to be welded, or where it is to be embedded in concrete. If there is a corrosion issue this steel will not be protected by the shop coat. What do we do about it? The bottom line is that a shop coat by itself gives a false sense of security and its cost is hard to justify. David Axt, AIA, CCS, CSI Senior Member Username: david_axt Post Number: 572 Registered: 03-2002 Posted on Wednesday, November 02, 2005 - 04:18 pm:    Doug, DBBS: Design/Bid/Build/Sue! Mark, Thanks!