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-   -   Lay plastic between ground and concrete slab? (http://www.diychatroom.com/f5/lay-plastic-between-ground-concrete-slab-38711/)

Flt_Simulation 02-19-2009 05:27 PM

Lay plastic between ground and concrete slab?
 
Below is a photo taken of my new house under construction here in the Philippines.

Before they poured the concrete slab, they installed a layer of plastic sheet on top of the ground ... and of course you can see the rebar on top of the plastic that will reinforce the cement.

A friend of mine told be that installing the plastic will somehow keep the concrete floor from drying completely and will cause problems later on when tile is layed over the slab (some areas of the finished concrete floor will have engineered wood planking with the required pad)

I would think that the plastic is a good idea since it will keep the damp earth below it from effecting the concrete slab above and maybe keep ground moisture from entering the house later on.

What do you folks think .... Good or Bad idea?

Thank's
Ron
Bacolod City, Philippines


http://i127.photobucket.com/albums/p158/Turbo6ta/24.jpg

DangerMouse 02-19-2009 05:35 PM

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

DM

Floorwizard 02-19-2009 06:43 PM

Quote:

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.....

jaros bros. 02-19-2009 06:57 PM

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.

DangerMouse 02-19-2009 07:20 PM

Quote:

Originally Posted by jaros bros. (Post 233174)
Concrete does not cure by drying out but through a process call hydration.

:yes:

DM

rusty baker 02-19-2009 08:59 PM

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

Mudd 02-19-2009 09:42 PM

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.

jordao 08-20-2011 04:37 PM

Quote:

Originally Posted by rusty baker (Post 233235)
In my area if you don't put plastic under the slab, it won't pass code.

http://www.buildingscience.com/docum...20under%20slab

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.

Philfun 04-22-2012 05:56 AM

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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