# Lay plastic between ground and concrete slab?



## DangerMouse (Jul 17, 2008)

i'd have to agree with you.... good idea.... heh

DM


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## Floorwizard (Dec 5, 2003)

> A friend of mine told be that installing the plastic will somehow keep the concrete floor from drying completely


I will not pretend to really know anything about this, but I would wonder how it will not be able to dry completely if the top side was exposed?

Now maybe if it was (sandwiched) by plastic.....


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## jaros bros. (Jan 16, 2009)

Concrete does not cure by drying out but through a process call hydration. Installing a barrier such as polyethylene below the slab retards the transfer of moisture from the ground to the concrete. Your friend sounds like he has heard an urban legend or he's pulling your leg.


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## DangerMouse (Jul 17, 2008)

jaros bros. said:


> Concrete does not cure by drying out but through a process call hydration.


:yes:

DM


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## rusty baker (Feb 13, 2009)

In my area if you don't put plastic under the slab, it won't pass code.


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## Mudd (Dec 29, 2008)

A plastic liner is good because it will stop some moisture from coming up through the slab... as long as it's the right kind of plastic.

The alkali in concrete will eat away at many plastics and disintegrate them over time.


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## jordao (Feb 8, 2010)

rusty baker said:


> In my area if you don't put plastic under the slab, it won't pass code.


http://www.buildingscience.com/docu...barriers/?searchterm=vapor barrier under slab

11. Concrete slab floors in ground contact are required to have a Class I vapor retarder below the slab in direct contact with the slab or rigid insulation having a thermal resistance of at least R-5 below the slab in direct contact with the slab.


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## Philfun (Apr 22, 2012)

Hi, I'm a new member who is building a house in Valencia (Dumaguete), Philippines.
I have not heard of inserting plastic between the ground and the concrete slab. However, you should definitely put some sort of barrier between any plastic piping, used in the plumbing for example, and the concrete slab or any other concrete. As Mudd said, if there is no barrier, eventually the concrete will eat away at the plastic piping and cause it to leak.


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