I would not put a vapor barrier under the pad regardless.
How to install vapor barrier on basement floor.
Any kind of persistent moisture will allow mold to get a foothold and soon ruin carpet or wood flooring.
The other option is to set the 2 4 wall framing in 4 from the masonry or concrete basement walls and use just the vapor barrier on the insulation facing toward the living space.
Before rolling out the underlayment be sure to sweep vacuum and remove all debris on the substructure.
If you have moisture on top of the foil you have a humidity issue in the house.
If you have a wine cellar or basement add a vapor barrier there too.
The area on which you are installing the vapor barrier should be clean.
A moisture barrier may or may not be needed to insure good adhesion of your vinyl floor so do your homework to avoid problems later on down the road.
Polyurethane sheeting is a typical vapor barrier that contractors use to prevent moisture from penetrating the walls of a basement.
Also be sure to use treated lumber for the bottom plate on the wall framing.
The material is stapled to the frame of a basement wall before it is finished with plaster or drywall.
A concrete floor with a too high moisture content can wreak havoc on a vinyl floor.
Tape all the seams to adhere the repair piece to the existing vapor barrier.
A vapor barrier consists of one or more layers of sheet plastic 6 mil visqueen on top of the soil in the crawlspace or basement.
Installing the vapor barrier is really quite easy as.
Cut another piece of vapor barrier material large enough to cover the damaged area by a minimum of 6 inches on all sides.
See what goes into waterproofing a basement too.
If after a day or two you have moisture under the foil you have vapor coming through your slab.
Too much humidity in a wine cellar can damage the corks and ruin the wine.
Water vapor can pass through building materials in several ways including direct transmission and by heat transfer but studies suggest that fully 98 percent of the moisture transfer through walls occurs through air gaps including cracks around electrical fixtures and outlets and gaps along baseboards.
A concrete floor seems like the perfect base for a vinyl floor installation.
How to install vapor barrier on concrete floor under laminate flooring always read the flooring manufacturers recommendations and instructions before installing the underlayment.
Those are the basic steps on how to install a vapor barrier under a concrete floor or slab.
A vapor barrier is also helpful to keeping a basement insulated and warm.
To properly determine if you have a vapor issue in your basement tape down some foil to the slab.
Because excessive dampness in a crawlspace or basement can condense you can install a vapor barrier to protect floor framing from becoming damp and covered with fungus efflorescence and rot.
Thus installing vapor barriers on wall surfaces must.
The science of moisture movement.