Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Vapor Barrier

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Jim Kestner wrote:
> 
> I would like to get opinions on what I consider conflicting requirements
> regarding vapor barrier under slab-on-grade. ACI 302.1-R, 2.4.1 requires
> that if a vapor barrier be used that it be covered with 3" of sand
> before pouring the slab. This minimizes plastic shrinkage cracking and
> curling. It also controls bleed water coming to the surface. This is
> logical and well documented. However, this procedure is risky when
> pouring a slab not under cover. What are the chances of rain occuring
> after the sand is placed over the vapor barrier but before the slab is
> poured? Now, you may have water trapped which could be very expensive to
> deal with or if ignored, worse than having no vapor barrier at all.
> 
> It seems like ACI requirements address the finishing and performance
> aspects of the slab, but have ignored the practical aspects of what the
> contactor must deal with. How do you other Engineers and Contractors
> deal with this?
> 

What are the chances of it raining before placing the vapor barrier?? 
If the subgrade or sand barrier gets wet (saturated) prior to the pour,
delay the pour.

I personally like using the 3" barrier when possible; however, half the
contractors call my office and tell me I have an error on my plans.

Brian K. Smith, P.E.