Concrete slab

[Humbleto]

I've got a quick question for some of you more knowledgable folks. I'm planning to put up a 30x50 metal building on a slab in the hill country of Texas. Should there be plastic (moisture barrier) under the rebar? The guy I'm using doesn't think there needs to be one. I'm leaning the other way. Any comments??

Thanks in advance

 

[Egon]

Use the moisture barrier [ plastic ] under the slab. It helps retain the concrete moisture for proper curing.

 

[CharlieTR]

Yes, absolutely put the plastic down, and under the rebar.
Why do he say no to?
consider getting another guy.

 

[flusher]

I've got a quick question for some of you more knowledgable folks. I'm planning to put up a 30x50 metal building on a slab in the hill country of Texas. Should there be plastic (moisture barrier) under the rebar? The guy I'm using doesn't think there needs to be one. I'm leaning the other way. Any comments??

Thanks in advance

I had a 24'x42' slab poured for my metal garage/shop in Jun05. Here's what it looked like before the concrete pour.
The black plastic is 10-mil Visqueen laid over about 4" thickness of gravel.

 

[EddieWalker]

The vapor barrier seems to be pretty common up North, but just about unheard of down here. From what I understand, it keeps the moisture from coming up from the ground and into your slab.

I've never seen anybody do this who works concrete for a living in my part of Texas. I've also never seen it done in California where I lived before here. Neither areas get any snow, so that might be part of it too.

One thing to keep in mind is that the dryer your mix, the harder it will be when it cures. I don't know how or if this has anything to do with moisture barriers or not.

Listen to your contractor. He knows the area that he's working in better than anybody else. There are reasons people do things different all over the country, and while I'm sure it won't hurt anything if you put a moisture barrier down, I don't know why you would want to.

Eddie

 

[gsganzer]

They put a vapor barrier under my slab when i had an addition put on. My 30 x 40 shop on the other hand doesn't have one. The floor will sweat under certain conditions, meaning that moisture migrates up through the slab.

In my opinion, put one down. What is it, $100 worth of materials. If put it in and don't need it you wasted $100. If you don't put it in and you did need it, then your screwed.

I understand what Eddie's saying, but there's an awful lot of contractors that do things wrong out of ignorance or laziness. How many concrete guys do you think really want to be bothered fooling with plastic sheeting? If they can avoid it, I'm sure they do. Maybe if you're on a true sandy soil, like some parts of Texas and California then it's not needed. I'd rather play it safe.

 

[CharlieTR]

I was taught that there are three "zones" for concrete slabs.
Dessert, Wet/warm areas, and cold areas, and that the vapor barrier is required in cold zones and wet/warm zones. But I have been wrong before (lots).

 

[mspaeth53]

The concrete company can add something called berlex to the concrete to make it water proof. Did my workshop that why and had no problems with water.

 

[HomeBrew2]

Pretty common in this part of Kalifornia. For the minimal cost, I'd sure insist on it too.

 

[BB_TX]

I put up a 30'x40' metal building in 2000 in Fannin county. I put up the building, but had a contractor do the slab for me. They put the plastic down under my slab. I didn't ask, he didn't say. He just did it.