Question of the Day - #118 Does membrane equal admixture

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Question of the Day - #118 Does membrane equal admixture

Postby RDavidson » Tue Dec 30, 2014 12:32 pm

The questions come in regarding alternates to the 5000 psi concrete footings and efforts to temper the cost result in all sorts of alternative requests. The code requires all footings to be 5000 psi or 2500 psi with an admixture or in some cases 3000 psi maybe with an admixture and maybe not. The alternate provided is the admixture which would result in a homogeneous mix and the entire footing would contain this homogenous mix. Questions include:
• Can I use a membrane on top of the footing? Is this equal to the entire footing being 5000 psi concrete?
• If I can use a membrane, what specifications should it meet? Could it be a sheet of 6 mil poly? Can it be spray applied? How about Thompson’s Water Seal?
• If I use a sheet membrane, do I install it at the time the concrete is poured or after it is cured? Can I penetrate a sheet membrane with rebar and if I install it after the rebar is set and the holes are bigger than the rebar, do I need to seal the tears or are some holes ok?
• If I can use a membrane, must it be applied on the sides and top, just the top?
• If it can be spray applied, should it be a surface membrane, a penetrating membrane, a breathable membrane, what?
• What is expected of pad footings? Or interior strip footings?

What is being regulated in R402.2 and Table R402.2 is compressive strength. That is the purpose of the section. As it is written, it appears that the intent is that the entire width and thickness of any footing is intended to meet the standard and a single membrane would not be equal to what is required in the code. The only hint that water and vapor resistance is an issue is buried in a footnote. What say ye?
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