I am working with my concrete contractor to pour the floor slab of the house I am building. He has already poured the footings, frostwalls, and basement walls. Here’s the question: The architect calls for gravel, then plastic vapor barrier, then poured floor. The contractor asked for vapor barrier, then gravel, then poured floor. I have always heard it done the way the architect requires, buit my contractor is insistent. What do you think?
Mike
Replies
Much as it pains me to agree with an architect--he's right. You put the poly on top of the gravel, and pour the concrete directly on top of it.
I can't imagine what your contractor's reasons are; putting the poly under the gravel would prevent water from draining downward, and unless you've got through-footing drains, any water that accumulates in the gravel will stay there, eventually weeping up into your basement.
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
I worked on a web site for a local concrete contractor and helped design an animation explaining why you put the barrier down first, then the VB:
http://www.stellarcontractors.com/
(Click on the WHY DO IT RIGHT graphic)
Granted, this is with slab on grade industrial.
In the end, though, this is just more proof that no two builders/contractors can agree on how to build a basement. ;o)
Here is a link to why the VP should be on top. I note that they are talking about using sand rather than gravel, but I think that the results are similar.
The is for a home and the main point it the control of moisture.
http://www.buildingscience.com/resources/foundations/sand_layer_under_slab.htm
Mike ,
1 reason your contractor does not want to put the poly right under the concrete could be, it would take 6-8hrs to set up for finishing under normal conditions in a basement that has a floor installed above it.
I agree. If this slab is inside in hot, humid weather, you'll be calling your float men back from home some time after midnight....that's not a mistake, it's rustic
How would adding accelerator to the mix affect the cure time and ultimate strength?
They added accelerator to the mix for my slab, poured directly over rigid foam with VB underneath, poured at 1:30 PM...last pass with the power trowel 9:30 PM. 24X29 one side open garage doors, temp about 75 degrees, dew point in the 50's.
An accellerator would reduce cure time, with no adverse affects on the concrete strength. ...that's not a mistake, it's rustic
Thanks...
I've always said: "That's not a mistake, it's ART!"
If you put poly under the cement all the water in the cement mix has to go up and can't go down. it takes a long time to set to the point they can float it and power trowel it. What makes it worse most cement contractors like to add water to the mix so it easier to level and move around. So there is more water that has to evaporate into the air instead of the ground. Now if you just put 4 inch of gravel between the poly and the cement the water can move it two direction and it will set up faster.