The pH scale measures all substances on a scale of 0 to 14. On this scale, 7 is considered neutral (e.g., distilled water). An acid is any substance having a pH of less than 7 with 0 being substances of greatest acidity. An alkali (or, base) is any substance having a pH of greater than 7 with 14 being substances of greatest alkalinity (or, basicity).
Technically, a pH test is a measurement of the concentration of hydrogen ions versus hydroxyl ions. We test pH using distilled water with a pH pencil or a pH litmus strip. The acidity or alkalinity of a substance is increasingly neutralized when water is added.
Substrate pH. There is usually a correlation between a higher moisture vapor emission rate levels and a higher pH reading. The pH test gives current conditions and does not indicated future conditions because concrete's pH is influenced by the concrete's moisture and other topical applications of adhesive, etc. If the pH of your substrate is either too high or too low, the adhesive used to bond to your subfloor (if a direct-glue installation) will release. Mohawk Group's NuBroadlok™ Premium Multi-Purpose Adhesive for their broadloom carpets writes that "pH must be between 5.0 and 9.0." The high alkaline levels can be brought down by an acid wash of the substrate.
Many beverages (e.g., orange juice or milk) are mildly acidic. Many detergents (e.g., hand soap) are mildly alkaline. Flooring can be permanently ruined if exposed to substances of excess acidity or alkalinity. For example, lemon juice can etch natural stone and cleaning agents of high alkalinity can strip color from carpet.