Archive through March 04, 2014

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Author Message Ronald L. Geren, FCSI, AIA, CCS, CCCA, SCIP Senior Member Username: specman Post Number: 1195 Registered: 03-2003 Posted on Monday, March 03, 2014 - 07:25 pm:    Client wants to "seal" the weathering steel after it has weathered to the desired color. The task is trying to artificially weather the steel before or after installation. Has anyone successfully "sealed" weathering steel? If so, what was used? And finally, what is the thinnest that weathering steel is available? Ron Geren, FCSI, AIA, CCS, CCCA, SCIP www.specsandcodes.com Justatim Senior Member Username: justatim Post Number: 58 Registered: 04-2010 Posted on Tuesday, March 04, 2014 - 08:02 am:    Not to answer your question, such sealing would replace a low- or zero-maintenance finish with a high-maintenance coating. Is the client willing to scaffold and re-seal the steel every 5 years or sooner? ken hercenberg Senior Member Username: khercenberg Post Number: 721 Registered: 12-2006 Posted on Tuesday, March 04, 2014 - 10:06 am:    I'm having a hard time getting my head around this one. First they want to intentionally cause the metal to rust and then they think they can put the genie back in the bottle? Rust blooms. It destroys concrete. Once the process has started, it doesn't stop until it runs out of material to oxidize. Putting on an acrylic or urethane coating, presuming you can get it to stick, won't contain the beast. Virtually every coating in our industry starts its instructions with "First, remove rust". Sorry. Just had to vent there. I think you might want to check into some high-end PVDF finishes out there. Hunter Douglas used to have some really cool coated panel systems that were warranted for 20 years not to change color. Ronald L. Geren, FCSI, AIA, CCS, CCCA, SCIP Senior Member Username: specman Post Number: 1196 Registered: 03-2003 Posted on Tuesday, March 04, 2014 - 10:46 am:    Justatim: Yes, I've explained that to them. Fortunately they don't want to do it to all the weathering steel on the project, just the railings for a small pedestrian bridge (they're worried that the rust will rub off onto people's clothing). Ken: I found waxing as a way of coating the steel. But then I found this coating from US Steel, which is a fluoropolymer coating that has the aged CORTEN appearance. I may suggest this as an alternative. Ron Geren, FCSI, AIA, CCS, CCCA, SCIP www.specsandcodes.com Dave Metzger Senior Member Username: davemetzger Post Number: 501 Registered: 07-2001 Posted on Tuesday, March 04, 2014 - 11:01 am:    Yes, until the finish has "set", it will indeed rub off on people's clothing, and hands. The project location affects how long it takes for the self-rusting process to run its course; the air must be sufficiently polluted in order to trigger the rusting/weathering process. I've been told that it is possible to pre-weather Corten, similar to pre-weathering of copper roofing to accelerate the development of the patina. I have specified this for copper, but not for Corten. ken hercenberg Senior Member Username: khercenberg Post Number: 722 Registered: 12-2006 Posted on Tuesday, March 04, 2014 - 11:04 am:    Interesting. How well does the wax stand up in exterior conditions, especially if subjected to handling? I'm curious if they have ever seen what weathered steel does to the surrounding surfaces. At applications I've seen this tends to migrate and stain 'downstream' surfaces. Hope they're receptive to the coating idea. J. Peter Jordan Senior Member Username: jpjordan Post Number: 694 Registered: 05-2004 Posted on Tuesday, March 04, 2014 - 11:10 am:    In your climate, this stuff will never stop rusting and will stain everything. I do know that they used to make steel sheet (was used on the stairs at Aloha Stadium which eventually became unsafe). You may want to mention that where there is a structural requirement (and railings fall in this catagory), it will have to be replaced. Sometimes you can tell an architect, but you can't tell him much. Ronald L. Geren, FCSI, AIA, CCS, CCCA, SCIP Senior Member Username: specman Post Number: 1197 Registered: 03-2003 Posted on Tuesday, March 04, 2014 - 11:25 am:    Ken: They are fully aware of (and I think counting on) the staining. Peter: I'm glad you mentioned the Aloha Stadium. My clients want to use it on the bridge decking and are still considering it. I'll use the Aloha Stadium as an argument against doing so. Ron Geren, FCSI, AIA, CCS, CCCA, SCIP www.specsandcodes.com Dave Metzger Senior Member Username: davemetzger Post Number: 502 Registered: 07-2001 Posted on Tuesday, March 04, 2014 - 11:29 am:    For the National World War II Memorial, we specified wax to protect the bronze fabrications. It was a custom blend of four microcrystalline waxes and polyethylene wax that was developed by the National Park Service for bronze statuary. It did stand up to exterior applications, but I understand it had to be reapplied annually. And yes, as Peter noted, in dry or non-polluted climates, the Corten rusting process will continue. In the early 1970's SOM designed a building (Uris Hall) at Cornell University in Ithaca NY, with the exterior envelope consisting of weathering steel Vierendeel truss framing and glazed openings. Because of the clean air in Ithaca, the steel patina took years to develop, and in the interim the building was a combination of rust and white streaks. Ellis C. Whitby, PE, CSI, AIA, LEED® AP Senior Member Username: ecwhitby Post Number: 214 Registered: 03-2003 Posted on Tuesday, March 04, 2014 - 12:03 pm:    Weathering steel is also a problem when salt can get on it: either coastal locations or near areas where deicing salt is used. As I recall some Midwest highway departments had to replace numerous bridges at overpasses. The weathering steel beams supporting the bridges kept “rusting” much longer and faster than anticipated because of salt spray from trucks passing under the bridges due to deicing salt spread on the road below. The steel beams were never able to achieve a “stable” rust surface. Richard L Matteo, AIA, CSI, CCS Senior Member Username: rlmat Post Number: 642 Registered: 10-2003 Posted on Tuesday, March 04, 2014 - 12:59 pm:    Okay gang - let's put this to rest. As one who worked for the Architectural Firm that developed HSLA aka "Corten" steel as a building material, once the rusting process has begun, there is no way to treat it. Ken H. has it right. The steel stops rusting after a certain point, but you cannot seal it. The more important question is why Corten was specified for handrails in the first place. If the railings are already installed, they would have to be cleaned using preferably an SSPC SP6 Commercial Blast, they primed with a zinc-rich primer and top coated with a high performance polyurethane coating from Carboline or Tnemec and I would consult with the product rep on the spcific prep and finish process. HSLA Steel for first used as a building material in the 1950's for the Deere & Company HQ in Moline, IL. It's still standing. Ellis and others who mentioned the issue with salt are also correct. Ron, Please feel free to contact me at rm4matt@gmail.com or 949-230-7523 and I can expand on the information. Robin E. Snyder Senior Member Username: robin Post Number: 514 Registered: 08-2004 Posted on Tuesday, March 04, 2014 - 03:43 pm:    Ron - I have used Tnemec 1079-0763 over corten and field rusted finishes. Still subject to the caveats all mentioned above by others. Ronald L. Geren, FCSI, AIA, CCS, CCCA, SCIP Senior Member Username: specman Post Number: 1198 Registered: 03-2003 Posted on Tuesday, March 04, 2014 - 03:52 pm:    Richard: It is for the guardrails and not handrails--I should have made that more clear. No handrails are required. Ron Geren, FCSI, AIA, CCS, CCCA, SCIP www.specsandcodes.com spiper (Unregistered Guest) Unregistered guest Posted on Tuesday, March 04, 2014 - 04:37 pm:    if I am not mistaken I believe it is also possible that adding a coating to Corten steel can actually lead to accelerated failures at localized flaws in the coating, sealer, wax, etc. It may be that if the steel is allowed sufficient time to weather and then is coated it may be okay but I am not sure there is sufficient time to allow such weathering since it could take months or even years and not days. Richard L Matteo, AIA, CSI, CCS Senior Member Username: rlmat Post Number: 643 Registered: 10-2003 Posted on Tuesday, March 04, 2014 - 06:27 pm:    Ron - If people are going to rub up against it, them I go back to my recommendation for prep and painting. If the project is in AZ, you can only use the inorganic zinc-rich primers due to the lack of moisture need to cure the organic primers. None of the projects I worked on where they used "Corten" ever used the material where the public could come in contact with it. We always used painted carbon steel.