Use Galvanized Steel? 2

[NFExp]

I designed a house on the ocean. There are a couple of steel beams and post supporting floor loads on the inside of the house (not exposed). I suggested that the steel be galvanized, the contractor is asking if galvanizing the steel is necessary since the beams are not exposed and are within the floor system.

I usually specify all steel to be galvanized when designing near the ocean but the contractor may have a point, Any thoughts?

 

[OHIOMatt]

I would use the arguement that since they are not exposed to view, there is no chance that they will ever see any maintenance. Also, no one will no if a problem is developing.

 

[MikeHalloran]

I had some offshore platform -borne equipment painted by a nominally three-step process that's supposed to be good for decades of exposure. Considering the expense of the very special paints and the manual labor involved in preparation, touchup and inspection, galvanizing would be cheaper.




Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

... also, I wouldn't trust a building contractor to not screw up a high-tech paint job.


Mike Halloran
Pembroke Pines, FL, USA

 

[MiketheEngineer]

While galvanizing will defintely lengthen the beam life - just not sure how good it will be. Even though it is not exposed - within a few years the cavity will be just as bad as outdoors. And as you build it the "bad" air will also be trapped in the cavity.. I think I would look at an epoxy paint of some sort.

We had a scaffold on an ocean beach in Florida. After one year - it was so badly corroded that we had to get out the Sawz-all.

 

[wannabeSE]

Before answering the contractor, I would ask him how much the credit will be for the client if the interior framing is not galvanized.

 

[Structcon]

As the owner to make the decision, since it is unlikely that corrossion of an interior protected steel post would corrode to a dangerous level before other deterioration was noticeable.

 

[racookpe1978]

I go with OhioMat: The steel IS exposed to humidity and air and salt - though perhaps at a lower level than if it were underneath a deck outside, but no interior covering like wood or wall panels or sheetrock is "watertight" and "humidity proof".

Invisible underneath drywall of a ceiling tile in the room below or decorative paneling, the corrosion will never be seen or corrected. House construction in today's AMerica is "built by the cheapest labor at the (illegal alien) pool standing outside the lumberyard. No training, experience, or knowledge should be assumed at any level of the crew, foreman, or contractor.

 

[TXStructural]

Galvanizing is probably not necessary since there will not be active wetting and drying. If the member is inside the conditioned envelope (not buried in insulation or outside the vapor barrier), then I expect that there will not be any reason to NEED protection. If it is under the bottom floor or in the attic, protected from the elements by a single layer of wood or drywall, or buried in insulation, I would probably want primer. Galvanizing is only necessary if you expect salt or water exposure over the life of the building (and be realistic about whether there will be maintenance of the envelope.)

 

[NFExp]

Thanks for the responses. We do business with this contractor alot and he also set us up with the Architect, so I am trying to save him money where we can. I tend to agree with TX structural but I also think that OhioMatt has a point and it seems the general consensus is that galvanized is required at a minimum. Since I can't find any literature that says I don't need galvanzied, I'm going to stick to my original recommendation.

Thanks

 

[moltenmetal]

Txstructural has it right: galvanizing is overkill for steel inside the conditioned envelope of the home. HD galv will cost a lot and will also render welding on site impractical. If all the framing can be detailed so that it can be bolted together you'll be OK with hot dip galvanizing, but when steel members are only part of the framing of an otherwise wood-frame home, details that use welding rather than bolting for final connections between steel members on site are often used. If so, they'll need to grind away the zinc, complete the welds and then touch up with cold galvanizing spray paint (zinc rich primer). In practice you'll get porosity in the welds due to incomplete removal of the zinc prior to welding- almost guaranteed.

If it were my home, I'd paint the steel with zinc-rich primer and be done with it.

 

[ron9876]

I agree with TXStructural. Have never heard of a problem with steel corrosion inside conditioned space. Primer is the typical coating for that situation in south Florida.

 

[TXStructural]

If you want to compromise a little, require a zinc-rich primer (ZRC or equal). It is not as protective as galvanizing, but when applied to clean steel, it provides enough protection for incidental moisture. I have two gates at my house. One was mill finish balk steel and one was wire-brushed and coated with ZRC. The black steel is all rust, while the coated one has only light rust color along some scratches where the coating has been gouged. The best part about zinc protection is that minor damage to coating does not cause structurally significant rusting in many exposures.