South Campus Miami Valley Hospital & Franklin County Courthouse

Posted on Posted in Suspension System for Cement Plaster

For decades, plaster ceilings have been suspended using 1-1/2” and 3/4” channel. The 1-1/2” is suspended from the deck, beams, or joists using 8ga. hanger wire and is usually spaced around 3’oc. I say usually because the spacing must be changed based on the span and the weight of the ceiling to be suspended from it. The 3/4” channel is then wire-tied to the 1-1/2” channel at a spacing determined again by the ceiling to be hung from it. These spacings are dependent on each other and the spacing of the members from which they are to be suspended. After the framing members are tied together, the metal lath is then tied to the 3/4” channel.

 

ASTM—C 1063 – 03 is the Standard Specification for Installation of Lathing and Furring to Receive Interior and Exterior Portland Cement-Based Plaster. Refer to it to find the specific spacing for your application.

“Standard” channel suspension system at the South campus Miami Valley Hospital.

As an option, a grid ceiling which is engineered for stucco and plaster have been developed. I will refer to the Armstrong system, although I am aware other manufacturers have systems which are similar.

The Armstrong Stucco/Plaster grid system has mains with routed slots at 13.5”oc so the cross tees snap together. This eliminates wire-tieing the channels together and it makes the spacing 100% accurate. The lath is then screw applied to the bottom face of the 1-1/2” tees. I recommend paper back lath so the thickness of the applied Stucco/Plaster is kept even. With standard suspension, paper-back lath cannot be used as the paper inhibits the ability to tie the lath to the channel.

“Snap-in” grid system used at the Franklin County Courthouse in Columbus, Ohio.

 

This exterior ceiling is 220’ above street level.

 

Note the studs laying on the framing - they will be put in as upright braces as part of the engineered uplift system. The carpenters are working off Hydro-lift mobile.

The greatest thing about the Stucco/Plaster grid system is that it is engineered. This means the hanger spacing, grid spacing, and up-lift bracing have all been designed into the system. Up-lift bracing has been accomplished in the past by standing up 3/4” or 1-1/2” channel—but it was never engineered or identified in the ASTM standards.

 

Another good thing about the grid systems are their ease of installation (labor savings). It is still critical to be plumb and straight with the 9ga. wires (you cannot just loop them like you might an acoustic ceiling grid, they must have square bends and tight loops or they will sag and cause cracks) but after the initial mains are properly suspended, putting together the rest of the system is a snap! If you have questions about the systems, or anything plaster, Ken Oren  would be happy to help!

The Dayton Bureau for Lath and Plaster is funded by contractors through the Dayton area Plasterer’s Union. It seeks to promote quality work through the use of trained craftsmen. If you have project details or specifications, Ken Oren is available for questions. There is no charge to architects when the project in question is offered to local bidders. The Bureau has purchased ASTM Section C and AutoCAD LT for reference and convenience in addressing design issues. If you wish to email an item for review to kenoren@plasterinfo.org, your query will be promptly addressed.

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