Atelier is right on the money as far as moisture testing is concerned and it is best to slab test on or right after high humidity and rainy days to get the worst-case-scenario test returns. The flooring system integrity will only be as good as it is in its worst day in the enviroment its installed in. After you get test results and compare them to the manufacturers product tolerances, then you can decide on the right product for that application or other remedies to bring it to withing manufacturer tolerances. The key here is prevention. Guessing isnt knowing, and any preventative measures used by guessing might be overkill OR might not be enough for the product. You just dont know without testing and in some cases an area will never be good enough for some products without rectifying the underlying construction causing the problem. Yes, some adhesives and substrate treatments will add a water vapor barrier and stop or stem hydrostatic pressure in the substrate but they all have cap limits. Owens Wood Flooring has a comptehensive information section of their site on Owens Plankfloor Gluedown Installation Owens states the following: "MAKE CERTAIN BUILDING INTERIOR AND SUBFLOOR ARE DRY Interior walls should be dry enough to be painted and a room temperature as required by adhesive manufacturer with a relative humidity of 30-50% should be provided before any installation begins. To determine if a concrete slab is suitable for hardwood flooring, please follow the NWFA guidelines to perform a Calcium Chloride test. If excessive moisture is present, do not lay flooring. Check floor in several locations. Concrete sub floors must be clean, flat and sound and of sufficient compression strength (3000lbs PSI) being sure that the surface is not slick. Sections not flat such as waviness, trowel marks, etc. are to be eliminated by grinding or the use of an acceptable leveling compound. Especially along the walls, the sub floor flatness must be checked and, if necessary, improved. Flat to 1/8" in an 8 radius. In addition to concrete sub floors, these products can be installed over dry, flat wood sub floors, such as plywood. If plywood is used as an overlay over an existing sub floor, the thickness of the overlay material much be such as to yield a total ¾" sub floor thickness. New wood type sub floors should also be checked for moisture using a moisture meter. In general, wood or plywood sub floors should not exceed 12% moisture content or 4% moisture content difference between wood flooring and sub floor." The NWFA is a resource you can only get information from if you are a paying member, so you might want to search around for the same information on calcium chloride tests from a independent source if you or your installer isnt a member. It should be noted that there are different types of moisture testing. 1. Relative Humidity of the Installation Area. 2. Moisture in the substrate itself hydrostatic Pressure. 3. Moisture testing the wood looring itself before the install to ensure its equalized to the within-tolerance installation area humidity. Here is some more information you may find useful: moisture testing hardwood flooring moisture testing for relative humidity in a room hydrostatic pressure in concrete ASTM F2170 ASTM F1869 your installer should be well educated in all of the above. ask them plenty of questions and get a good comfort level in their abilities. ask for and check out their references too.

Funny you posted this today ! I was just meeting with a man for my new home flooring and we discussed the moisture level in slabs. I too am on a slab and he suggestes that I have a test done before we determine the appropriate flooring. He did tell me there is a moisture barrier that can be put down (sorry, I can't remember what he called it) he did say it was expensive around $3.00 sq. ft.

Concrete will just wick moisture everywhere that it’s attached to. The framing and any vanity that touches the floor will rot out pretty quickly. An epoxy kludge isn’t a substitute for proper construction practices that include proper waterproofing for wet spaces. If you want the look of a concrete shower, then you can go the traditional construction method and use a micro topping over the cement board walls. You would need to pay attention to proper detailing to the max and have a capillary break installed all the way around where the micro met the existing. Not cheap. There is nothing magic that is cheap and that would provide acceptable conditions for a wet use area.

I can tell you I don't know much about carpet. But I can tell you concrete needs to breath. I would recommend a moisture test reading before putting anything down. Old carpet was much common on concrete then nowadays with requirements.