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.

Be sure you understand the options. There are 2 kinds of crawlspaces allowed by the IRC: Vented and Unvented (aka "sealed"). The terms "unvented" and "sealed" are misleading because this type of crawlspace is not completely sealed or unventilated. The IRC code requires that both of these types of crawlspaces be "ventilated" so that moisture does not collect and encourage the growth of fungus (whether from the ground, condensation on the slab, etc.) by one of the following methods: 1) "Vented" Crawlspace - install vent openings in the exterior wall of the crawlspace 2) "Unvented" Crawlspace - inside the house supply to or exhaust from the crawlspace a small amount of air with a return air path to or from the house and insulate the exterior walls of the crawlspace. Both crawlspaces must have a vapor retarder at ground level and an access opening. For more information see IRC section R408.1, 2, & 3.

These combination adhesives are fine. Almost all of today's residential slabs are poured using a moisture barrier (plastic) below the concrete. These aren't fool proof, but they do 90% of the moisture resistance. So long as you pay TOP dollar for your adhesive, you should be fine. To assess the quality of a product in this category, you should be paying $80 - $120 per gallon (or more for these 4-in-1 products). Their spread rate should be 30sf per gallon (or less). This makes the price (roughly) $3/sf - $4/sf. A 1000sf of basement will require 33 - 35 gallons of product (which is why they often come in 5 gallon buckets). You can see why a glue down, below grade hardwood install is a BIG price tag. The adhesive alone could cost $4K for 1000sf below grade. The labour is EXTRA. The one thing to remember: all adhesives need a prepared concrete to stick to. The slick concrete surface you see now will have to be ground/shot blasted so the adhesive has something to grab. Slabs are chemically cured in today's building conditions. They ADD chemicals to help the water evaporate faster out of the slab. These chemicals MOVE to the surface of the slab and are considered contaminants/deposits that MUST BE ground off. Once the concrete has been roughed up (and flattened at the same time), you should be fine with this level of adhesion/moisture barrier. Be prepared for another $1-$2/sf for the grinding/shot blasting.

Here is an article to read: http://tenoaksflooring.com/publications/Glue%20Installation%20Instructions.pdf The suggestion is you may glue directly to concrete subfloor with just Wakol MS 260 Adhesive if the VOC moisture is zero. If you have moisture it is recommended to use Wakol PU 280 Moisture Barrier first and then glue down with MS 260 Adhessive. Video of applying Moisture Barrier: https://www.youtube.com/watch?v=978TsRewzpE Video of gluing floors to concrete slab: https://www.youtube.com/watch?v=AEWgfDBuqEQ