We have been asked provide a solution for an issue with the roof of a car wash. The 12-year-old structure is concrete block walls. Roof structure is open web steel joists. The OWSJ are exposed at the underside. The roof deck is hi-rib steel. Roofing is composite over rigid insulation. The upper and lower chords are showing rust. There is no condensation on the underside of the deck. A suggestion given was to strap the underside of the OWSJ and apply plywood sheeting and a vapor barrier. I prefer to consider leaving the joists exposed and coat the joist with some sort of asphalt coating. The epoxy paint that is on the joists is pealing. Has anyone dealt with this issue.
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Rust on steel joists
- Thread starter rittz
- Start date
JedClampett
Structural
A lot of us have dealt with rusty joists, although a car wash is kind of unusual.
I agree with you that hiding the joists is a bad idea. I'd blast them, and recoat with an epoxy. Alternatively, you could use an epoxy coating that bonds to the corrosion. However, I disagree with the asphaltic coating. IMHO, epoxy coatings are the most protection for your coating buck.
Note that no matter what you do, joists are going to corrode. They have so many nooks and crannies that are hard to coat, that they're just susceptible to rust. But to me, that's another reason not to hide them. At least when you can see them you know what you're dealing with.
I agree with you that hiding the joists is a bad idea. I'd blast them, and recoat with an epoxy. Alternatively, you could use an epoxy coating that bonds to the corrosion. However, I disagree with the asphaltic coating. IMHO, epoxy coatings are the most protection for your coating buck.
Note that no matter what you do, joists are going to corrode. They have so many nooks and crannies that are hard to coat, that they're just susceptible to rust. But to me, that's another reason not to hide them. At least when you can see them you know what you're dealing with.
I also agree that hiding the problem is a very bad idea. My suggestion is to use a light sandblast to clean off the worst of the rust, and then spray the whole roof soffit, joists and deck, with a coating that is forgiving of poor surface preparation. Carbomastic 15 would be my choice.
But hiding makes the problem go away doesn't it? ![[bigsmile]](/data/assets/smilies/bigsmile.gif "[bigsmile] [bigsmile]")
Actually - if you had a significant mechanical venting system that constantly dehumidifies the air in the enclosed space (using a poly sheet ceiling system) it might work ok -
simply by keeping the enclosed space fully vented and dry you could then paint the joists with something less than a high cost epoxy.
However, the mechanical system might cost more in the long run based on life cycle costs of the equipment, energy, etc.
Actually - if you had a significant mechanical venting system that constantly dehumidifies the air in the enclosed space (using a poly sheet ceiling system) it might work ok -
simply by keeping the enclosed space fully vented and dry you could then paint the joists with something less than a high cost epoxy.
However, the mechanical system might cost more in the long run based on life cycle costs of the equipment, energy, etc.
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