Vapor barrier under 2" foam
- Thread starter matt60j
- Start date
now im confused. It always seems like people pour directly onto thier foam. -MATTSteve in Mi
Well-known member
I put the 6 mil polyethylene film under the 1" Dow rigid (blue) foam. If it's a good idea to keep the water out of your concrete floor I figure it is even better to keep that water out of your foam insulation.
Where did you get your foam and how much is it? Also what is the psi rating? Thanks. -MATT
rburke65
Well-known member
I thought you put the film down, then the foam, then the wire, (pex,) then concrete.
Steve in Mi
Well-known member
I purchased ~200 sheets for my shop build in 82' from the Dow employee stores in Midland and Bay City. It will do no good to tell you the cost, it can't be purchased for that price today and it will only make you cry.
In addition to the foam under the floor I put an inch both inside and outside my block foundation walls and continued the outside 1" upward to encapsulate the entire 2 story building. 2" X 6" stud cavities were filled with R-19 fibreglass.
overkill 19
Well-known member
When I pu SM on my walls, no need for VB as the foam is its own VB. different codes in diff areas though.
Willy Victor
Well-known member
- Joined
- Apr 9, 2006
- Messages
- 444
Overkill is correct, foam is it's own vapor-barrier.
Willy
Willy
I'm crying alright, 70 sheets at $20 a sheet. Employee stores are nice. I work at the old Dow plant in Bay City but I can only get bags candles cleaners etc. -MATT
http://www.concretenetwork.com/vapor-barriers/installation.html
this is one post, I will look for more
this is one post, I will look for more
My argument about the vapor barrier on top of the insulation. The concrete needs to retain its moisture during the curing process, to maintain a lower heat cycle. By having the vapor barrier under the insulation, it created voids in between the panels for the moisture to run too. So the bottom half of the slab dries quicker than the top half. the slab curls. Then it cracks. This is also the same principal of pouring without vapor barrier.
Now contractor love pouring without vapor barrier because they can pour it wetter and the water will wick out the bottom and dry quicker, but the slabs cracks. so now we are at the point, "all slabs crack". No, they don't, only those that are done wrong.
So you in the business of placing concrete, you want to place wet, due to less man power. You don't want vapor barrier because, you don't have the manpower to install it and you have to buy the vapor barrier. You want the concrete to set quick, so you can go home early and stop paying labor. Oh all concrete cracks.
Correct way is to use a vapor barrier on bottom against the concrete, on top of the insulation or rocks. Then after placement wet slab and cover with another vapor barrier for at least seven days. You got to go into the placement, trying not to create cracks.
Now contractor love pouring without vapor barrier because they can pour it wetter and the water will wick out the bottom and dry quicker, but the slabs cracks. so now we are at the point, "all slabs crack". No, they don't, only those that are done wrong.
So you in the business of placing concrete, you want to place wet, due to less man power. You don't want vapor barrier because, you don't have the manpower to install it and you have to buy the vapor barrier. You want the concrete to set quick, so you can go home early and stop paying labor. Oh all concrete cracks.
Correct way is to use a vapor barrier on bottom against the concrete, on top of the insulation or rocks. Then after placement wet slab and cover with another vapor barrier for at least seven days. You got to go into the placement, trying not to create cracks.
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Engine-Ear
Active member
Interesting thread.
"I thought you put the film down, then the foam, then the wire, (pex,) then concrete." -burke65
Me too...Now that I reviewed pics of my own slab, and contrary to brownbagg's point of view, I realize that my concrete guy must have felt that the foam was the vapor barrier, too. Brownbagg, I agree with your logic, BTW.
"I thought you put the film down, then the foam, then the wire, (pex,) then concrete." -burke65
Me too...Now that I reviewed pics of my own slab, and contrary to brownbagg's point of view, I realize that my concrete guy must have felt that the foam was the vapor barrier, too. Brownbagg, I agree with your logic, BTW.
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overkill 19
Well-known member
My father in law just poured a slab last week, he used a new product that is a vapour barrier and sm foam all in 1. it had a seal adhesive flap for the joints and came in 4 foot wide roll and was some what flexible to form to the contours of the ground. It comes in 3/4 or 1 1/2 probably other sizes too. When I pour mine next year I'm going to use the 1.5 on the edges and 3/4 in the middle. Seamed like a very tough product. I will look up the brand name when I take to him next.
overkill 19
Well-known member
Just a quick point about pouring concrete too wet. Dont do it! When concrete is strength tested, too much water is not good. For slabs I beleive it would not make a big difference, in commercial it would. Sometimes people misunderstand plasticisers and retardants, for just too wet. Plasticizers make it easier to work and retardants extend working time. Both of these do not signifcantly decrease strength.