Finishing a basement and have a question about the concrete floor. When they were building my house, I was able to watch exactly how they laid the concrete slab floor for the basement. I am not sure if it is common in most areas, but basically what they did in my place is put down 4 inches of crushed drainage gravel, covered that with a plastic membrane (polyurethane I think) and then pored the slab. I was told by the builder that this is done to prevent moisture penetrating the slab.
Anyway, I am wanting to put down some laminate flooring, and was going to just put down an underlay, but while doing research, every site I go to suggested putting down some type of moisture resistant sub-floor.
So, my is this. Given how they build the slab floor, how much of a moisture barrier do I need to put down. Is a combination underlay (felt and poly) going to suffice, or do I need to use a pre-engineered sub-floor product (like thermacore or dricore)?
Double felt: Two layers of #15 asphalt saturated felt paper that meets ASTM Standard
D-4869, with the first layer adhered to the slab in a skim coat of appropriate adhesive,
and a second layer adhered to the first layer with appropriate adhesive.