Historic Theatre Renovation - Existing Plaster Dome Weight

[Struct_Dre]

Hello All!

I'm working on a historic theatre renovation and the architect just let us know that they plan to add acoustical plaster to the existing plaster dome. I'm trying to determine if the additional weight is more than the allowable 5%, but I cannot determine the weight of the existing dome. ASCE gives the load for ceiling plaster as 5 psf on tile or concrete and 8 psf on wood lath. These loads do not allow us to consider the thickness of the plaster used and I'm assuming that the plaster used for a theatre's decorative ceiling dome is thicker than traditional ceiling plaster. Does anyone have any insight on this or possibly a resource for plaster load by thickness?

Any help is appreciated!!

 

[Ron247]

Plaster is a generic term for something that is applied in thin layers. You need to know what your plaster is made of to get a somewhat accurate weight. Plaster of Paris is listed as 50-55 pcf but they never say if that is the dry powder weight or the finished product dry weight. They may be the same, I do not know. There is a portland cement plaster we call stucco that I think weighs more than plaster of paris. What they are calling plaster at your project may be stucco.

 

[Struct_Dre]

Well I'm doing some research now to determine the type of plaster used. What I know right now is that it is the historical plaster used in the 1920's (Baltimore,MD), 3 coat, on metal lath. I'm still looking for what type of plaster this would be, but haven't had much luck.

 

[JAE]

Check here for a good overview from the US National Park Service:

https://www.nps.gov/tps/how-to-preserve/briefs/21-flat-plaster.htm

In this they talk about the use of lime vs. gypsum plaster and rough dates for when they switched between them.

A slide show with some interesting comments on failed repairs and current solutions:

http://www.ccfm.net/wp-content/uploads/2018/04/plaster-on-wood-04-10-18.compressed.pdf

I'd agree with Ron247 on the 50 to 55 pcf density range.


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