pH is the value used to express the acidity and alkalinity of a substance. Based on a scale of 0 to 14, pH 0-pH 6 represent substances that are acidic, and the values pH 8-pH 14 indicate alkaline materials. A pH of 7 is neutral. The relative strengths of various substances increase as the values move away from pH 7 in either direction. For example:
pH 0 – Hydrochloric Acid
pH 4 – Orange Juice
pH 7 – Pure Water
pH 9 – Borax
pH 14 – Sodium Hydroxide (Lye)
Let’s take a quick look at the mathematical application. The key word here is “log.” Log refers to the fact that each unit change in pH represents a ten-fold change in the strength of the material being tested, i.e. a pH of three is 10 times more acidic than a pH of four. Conversely, a solution with a pH of 11 is 10 times more alkaline than a pH of 10.
This becomes more interesting when one considers that pH levels range from 0-14, meaning they represent a span of 0 up to 1x10 to the 14th power, an incredibly large scale of measure.
There are three methods that can be used to measure the surface condition of a concrete slab: The pH paper test; the pH pencil test; and the pH meter test. (photo 1) In all three tests, the slab must be clean and free of any sealers, curing compounds, paints, oils, adhesives, or residues. This can be accomplished by either a light scraping or sanding of the concrete. A light abrasion of the surface is all that is necessary. Care should be taken not to penetrate the concrete too deeply, as alkaline readings will be artificially high. (photo 2)
For all pH testing, either distilled or de-ionized water must be used.
pH Paper TestStep 1: After cleaning the surface of the concrete, apply a 2-inch diameter puddle of distilled or de-ionized water to the surface of the concrete. Allow the solution to set for one to two minutes. (photo 3)
Step 2: Place the pH test strip into the solution and allow it to become saturated. (photo 4)
Step 3: Compare the pH test strip with the color chart to determine the alkalinity. The pH paper measures alkalinity in half increments. (photo 5)
pH Pencil TestStep 1: After cleaning the surface of the concrete, dampen a 2-to-3-inch diameter area with distilled or de-ionized water. Do not allow the water to puddle. (photo 6)
Step 2: Mark an “X” in the dampened area with the pH pencil. (photo 7)
Step 3: After one to two minutes, compare the pencil mark with the color chart to determine the results. (photo 8)
pH Meter TestStep 1: After cleaning the surface of the concrete, apply a 2-inch diameter puddle of distilled or de-ionized water. Allow the solution to stand on the surface for two or three minutes. (photo 9)
Step 2: When the allotted time is up, place the surface probe of the pH meter into the solution. Hold the surface probe in the solution for about one minute, or until the meter stabilizes. Care must be taken when using a surface probe, as the tip is made of a thin, glass-like substance and is easily cracked or scratched. This will cause the meter to malfunction.(photo 10)
The most destructive area of moisture problems is the slab’s alkaline condition. Alkalinity, far more often than moisture, is responsible for the destruction of adhesives and materials.