The best way to prepare the slab for a moisture & pH test, is by shot blasting or grinding which requires special equipment. Here, a portable surface grinder with dust collector is an ideal tool for obtaining a clean surface area. Grind cleanly, at least 1 square foot of area for each test (20x20 inches per ASTM F-1869). Allow the area to remain open for at least 24 hours (per same) before installing tests. When special tools can not be obtained for preparation, try using a razor scraper to remove debris followed by a bit of work with a wire brush. Test results can vary according to the type of floor surface profile. However, the logical method is to test over the same kind of surface profile the floor will be installed upon.