Vapor barrier under concrete?

[fflintstone]

I was planning to put a vapor barrier under the concrete and I am about to pour. Two different concrete guys have given me weird looks when I tell them that. What are the pros and cons? Its $80 for the plastic and my funds are limited.
I am on a sand hill and I had to soak the ground over night two nights in a row just to get it so I could work it with the loader blade.
Thoughts? Opinions? Links to REAL technical data?

 

[londonsteve]

It's definitely best practice to use vapour barrier and is code almost everywhere. We are dong a lot of bases with vapour barrier and thermal insulation, costly but nice in the winter.

 

[aqr81]

I'm not familiar with soil conditions, or water table levels in your area. I can tell you that where I am, logically there would be little concern or need for it; regardless, it is a code requirement. I generally approach these type of things as "better safe than sorry". Other than the additional costs, I am not aware of any cons.

 

[bmwpower]

Put it in for sure. My concrete guy gave me the same looks, but he got over it. If you ever want to coat the floor, tile, etc. you will want a vapor barrier down. How much do you need? You have seam tape?

 

[larry_g]

http://www.stegoindustries.com/docs/Vapor Barriers Under Concrete Slabs.pdf

The above link gives some good information on your question. If BMWpower is correct then read the section on finishing and the finishers poking hole in the VB to get things to cure.

lg
no neat sig line

 

[fflintstone]

wow! posted this and I did another lap around with the rented compactor.
I come in and 4 replys allready! Great! I will get the laser out toning and see how much it compacted.
I am going to check out the link, Thanks.

 

[bmwpower]

http://www.stegoindustries.com/docs/Vapor Barriers Under Concrete Slabs.pdf

The above link gives some good information on your question. If BMWpower is correct then read the section on finishing and the finishers poking hole in the VB to get things to cure.

lg
no neat sig line

I remember that document. Yes, don't let them poke holes or otherwise break the barrier anywhere. That's why it's good to have seam tape handy in case they do. My guys had to jockey wheelbarrows around but the barrier held up. I had the tape ready in case they ripped it.

I went with this stuff. Great product - no problems for me.

http://ravenefd.com/pdf/Install/VB-Install.pdf

You can see the seam tape in use.

 

[Qtip]

Yes do it ...also may what to put rigid foam down

 

[fflintstone]

given my soil conditions and after reading that link I am actualy less inclined to use it, but if I do I will have to make sure they put less water in the concrete mix.

 

[nmanitou]

I think you are on the right track. The real question is what are your soil and groundwater conditions. If, as you described your soils are sandy, well drained, with a low water table and no potential contribution from stormwater runoff, then the vapor barrier is not need and may unnecessarily complicate finishing.

People's experiences with this topic depend in their region and site conditions. VB's are needed in some situations. I live in Michigan also and have built on several similar site to yours without issues related to moisture on the slab.

 

[BillGalbraith]

The pronlem that I found with Stego si that I had to buy a whole roll of it, at $350. I used 28x28, so I still have a bunch of it left. It will go on CL one of these days, but I don't expect that it will sell. If $80 makes you flinch, you will really pucker when you price out the Stego.

 

[Justanoldguy]

In NZ VP is used under all floor areas. Building regs require it.
It takes a bit longer to cure sure, but that is an upside as
quick curing concrete tends to crack more often.

 

[gdf_77]

have you looked into bonding a ground rod. A couple of years ago, in my electrical theory class, this came up. You may just want to check with an electrician and inspector. The reason being that concrete has a natural conductivity, and since it isn't touching the earth with the vapor barrier, you might need to add one, bonding it to the rebar and a ground rod.

 

[fflintstone]

FYI I purchased 6 mil black seating for a vapor barier.

 

[bassr38]

It's good to put a vapor barrier they say now days but I have been a mason for 40 years. Back in the day we use to get the grade ready then rock it and then pour concrete. Now days they have modern technology, at lest that's what they call it, I think the verdict is still out.