Macv, it's interesting that you bring up the product Preprufe. This is a pretty high-end waterproofing product. It was my initial understanding that Preprufe was primarily a commercial application, but the more I've spoken with waterproofing experts, I'm learning that it does get used in high end residential projects. It's very very expensive, but it is the ultimate in below slab waterproofing. If you wanted the absolute best waterproofing, you would use Preprufe under the footings and under the slab and have the preprufe lap around the edges of the footings, then you would overlap the outside walls and outside edges of the footings with bituthene. The bituthene would overlap the preprufe at the footing and the entire foundation would be waterproofed. This is the best waterproofing money can buy, but you'll pay for it, as I believe that Preprufe is about $1000/roll and each roll covers about $300 sq. feet. I am in the initial planning stages of a build in Mass. and if money allows, I'll be doing my basement waterproofing in this method. Of course, on top of the bituthene you'll want 2" of XPS (R-10) and an exterior french drain and you'll never have basement flooding issues. Macv, do you see much Preprufe used in your work on residences?

Look at Hydroment's Ultraset. It's a trowel-on membrane. An excellent adhesive, a moisture barrier, and a crack isolation barrier all in one. For the areas that will have RFH, you can use the Ultraset as an adhesive to set something like Cerazorb, a synthetic cork. Some folks do use 1/4" or 6mm thick true cork on the slab to act as a thermal break, just make sure it's not a low-density cork and that it's recommended for that purpose. There are RFH websites that sell a proper cork product. The RFH can then go over the Cerazorb/cork. OR you can use the Ultraset to adhere RPM mats (or equivalent) to the slab and install your RFH over that. RPM mats will act as a therma break, even though they have a negligible R-value. RPM mats are lugged mats, the lugs act as anchors for weaving RFH wire. While the RPM mat has little R-value, cork on the other hand has an R-value of about R3, so you'd get roughly R 0.75 from a roll of 1/4" cork. In the areas that won't get RFH, you can use Ultraset to adhere 1/4" cork/Cerazorb to the slab, then install a floating engineered flooring over the cork. 1/4" thick Wedi board can also be used instead of cork/Cerazorb, etc. All those are low-profile options. You'll get a bit of a thermal break but very little improvement in R-value. If you want more R-value, look at sheets of XPS. XPS comes in 4' by 8' sheets and is about R5 per inch. As you can see there are numerous ways to get this done. Some products have certain advantages over others.

I can tell you that the cork would be SOGGY if you had moisture in the slab. The vinyl on top would have sped this up. It would have looked black and moldy when you removed the vinyl. If it looked dry and intact, you are fine. I would run the wood right over top and take my chances. I'm sorry you had to find out the hard way about vinyl and underpad. The installation instructions on the vinyl would have pointed that out.

Yes, concrete slabs will absorb moisture from walls and moisture will wick and dry from floors -sponge effect. You always want to maximize your vapor barrier system for permanent installation. Minimum system equals high risk of floor damage.