ductbank forms

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mshields

mshields

Senior Member
Location
Boston, MA
Just received a call from a contractor wanting to know if he could use sheet rock in lieu of plywood to build form for ductbank, assuring me that he had done it before without problem.

Not sure if I should accept this or not, the material obviously subject more to warping than plywood. Does anyone have experience with this?

Thanks,

Mike
 
I would be concerned about the strength of the sheet rock if the concrete is deep or if the supports were spaced too far apart.
But if the mechanical concerns are properly addressed I do not see a problem.
Removing the forms may get messy if the paper sticks to the concrete.
The rock probably will not absorb enough water to interfere with curing at the surface.
 
The last job I was on the contractor used this mesh

http://amico-stayform.com/products.htm

Maybe a good alternative/compromise?

Based on how I've seen concrete dumped into duct banks I would not trust the strength of the sheet rock.

Mix strength/ design would be a big determining factor

Also if there is any water in the trench and or rain/snow, I can see the sheet rock falling apart.

Joe Villani
 
The form is just there to keep the concrete in place until it hardens. As long as the final product meets the specification for the duct bank do you really care what is used for the forms?
 
infinity said:
The form is just there to keep the concrete in place until it hardens. As long as the final product meets the specification for the duct bank do you really care what is used for the forms?
Click to expand...

I agree, who cares. Contractors cost if it spills over and he uses more concrete then expected. Heck, I'd probably leave it in place and back-fill over the top of it; if environmental folks don't care.
 
Joe Villani said:
The last job I was on the contractor used this mesh

http://amico-stayform.com/products.htm

Maybe a good alternative/compromise?

Based on how I've seen concrete dumped into duct banks I would not trust the strength of the sheet rock.

Mix strength/ design would be a big determining factor

Also if there is any water in the trench and or rain/snow, I can see the sheet rock falling apart.

Joe Villani
Click to expand...

Stayform is not good for electrical duct banks. It can create a Faraday Cage effect.
 
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