Old steel bar joists with expanded metal lathe and concrete topping 1

[Ingenuity]

I have a site inspection today where it has been described to me that the very old parking garage suspended deck is framed with steel bar joists supporting a concrete slab.

BUT...the concrete slab is NOT formed with a metal deck but on (quote) "...plaster with expanded metal lathe...". The bar joist spacing is approx 24".

Apparently the metal lathe is badly corroded, and numerous spalls to top concrete surface too.

My guess is the building is 25+ years old.

Any one have any experience with "plaster forms with expanded metal deck" with a bar joist system.

TIA

Mark

 

[JAE]

If the lath and plaster (can't believe they used plaster)were only used for temporary forms for a reinforced concrete slab...then your focus should be on the reinforced concrete slab...not the rusted lath as its purpose and use is in the past.

However, the plaster (if that's what it is) would retain moisture for a long period of time, along with porousity for oxygen and , voila - we have the potential for an aggresive environment on the underside of your slab. Try to see what the full make-up of the slab system is and inspect the rebar if possible before making any conclusions.

 

[Ingenuity]

JAE,

Many thanks. I too cannot believe that plaster reinforced with metal lathe was used as temporary stay-in-place forms too.

Concrete slab cracks and water leakage have resulted in significant spalling of the concrete and also corrosion to the top chord of the bar joists (moisture trapped in plaster, as you described). The location is 1/4 mile from Waikiki beach - coastal chlorides!

I will review the framing in a few hours and see for my self what was actually constructed.

Thanks for your input.

 

[JAE]

Oooo - can you hire me to come with you and inspect the garage too? Please!

 

[Ingenuity]

I was in Las Vegas for 3 days earlier this week - 32F on Monday morning - what a shock. Good to be home at 75F, sunny, and a lunch-time outdoor swim planned! Sorry

 

[JAE]

sigh

 

[samdamon]

A leaky old parking garage framed with owj near the ocean. Can anyone say "bulldozer"?

 

[Ron]

Ingenuity...if you look closely, you'll probably see that the lath and plaster were not used as formwork for the concrete, but were likely added later for fireproofing or other pseudo-protection.

 

[connect2]

right Ron on the fire protection possibility.
We have seen a number of buildings +/- 1930's in which metal lath was used as a form, becoming redundant after the concrete had cured. In these cases the lath and let me say in quite 'sagged' condition full of concrete, was visible and not covered. These systems were generally combined with light weight concrete and then a topping. Kidder Parker has several comments on their use at the time. Parking structure ... thats unusual from our experiences and will present quite a challenge.

 

[Lutfi]

Years ago they used bulb tees with chicken wire type reinforcement and they used gypsum type decking. This may be what you have. Check on the joist spacing and see if it is close to 48 inches on center.

This system was used for roofs.


Regards,
Lutfi

 

[Ingenuity]

Thanks for the additional comments.

I visited the site on Friday afternoon and was given a CD of scanned original drawings.

It is actually a single parking level serving a small 10-level hotel.

Designed/constructed in 1961 +/-. Steel bar joists at 24" centers supporting 2.5" thick LIGHTWEIGHT concrete slab with 6x6-10/10 WWF on HIGH-RIB metal lath. 1" min asphalt topping is detailed on drawings but removed some time ago and possibly topped with concrete and a waterproofing membrane that has long-since deteriorated. The high-rib metal lath is paper-backed. I could not see any plaster application to the metal lath.

The soffit of the steel joists framing is furred with 3/4" deep furring channels and dry-wall for 3-hr fire resistance.

Concrete slab has deteriorated extensively (spalls and delamination) with extensive corrosion to top chord of bar joists.

The paper-backed high-rib lath was NOT installed after the 2.5" concrete slab as the lath passes over the top chord of the bar joists.

Was this metal-lath with 2.5" concrete a common form of slab framing back in the 60's?

 

[MikeE55]

I believe what you are describing was called steel-tex. It is a black paper with steel lath, draped across the joists. It was used in the 50's - I don't really know how common it was. Typically it's topped with lightweight gypcrete. I have only seen it used for roof decks.