The Importance of Moisture Testing

In the summer of 1981 a friend called me to ask if I would be interested in moonlighting to help him install floor sealer for a company in California. Even though I worked 18 hours that day, I decided to take my friend up on his offer. The job started my career in the concrete floor specialties industry.

Back then, our industry was not very scientific: “Coat It! Coat it! Coat It!” was the answer to almost everything. Not much attention was paid to testing or careful engineering of a concrete flooring system to avoid what today are knee-deep liabilities. Shot blasting was not yet prevalent. We used silicon carbide cup stones on shroudless grinders and everything was prepped with a muriatic acid and water mix with no diamond tooling.

The main testing performed on a concrete slab before our work was a visual inspection. If the coatings peeled, we surmised it was from not rinsing the acid properly. White residue meant efflorescence and a possible moisture problem, but was that really it? Or could it be topical deposits caused by hard water or etching?

At the time, water vapor emission tests were done by simply duct taping a square of 6 mil plastic to the slab and checking if it was wet after 24 hours. There was no way of knowing exactly how much water vapor was transferring through the slab. I didn’t know what water vapor transmission really was. These tests only concerned concrete coatings and hard surface flooring since concrete polishing was more than a decade from becoming a viable hard surface flooring choice.

Moisture testing and polished concrete

To a company that only engages in concrete polishing, why is moisture testing important? After all, why would you care about moisture? You are not selling products that can peel and delaminate. On the other hand, how many times have you met with a potential customer that is choosing between polished concrete and resinous or vinyl tile? Advanced moisture testing can also be done with ASTM 1869 calcium chloride and humidity probes. Conversely, with a simple pH test kit you can demonstrate that the floor is emitting water vapor and the value engineered choice is polished concrete. If the floor is producing more than 3 pounds of water vapor, which is past the parameters that flooring manufactures allow, the litmus paper will turn dark blue at the surface.

If the floor is showing a high moisture problem that also visually indicates an underlying contaminating substance such as sodium sulfate being transmitted from under the slab and deposited on the surface, it is best to do further testing as efflorescence will form on the finished polished concrete. The customer may associate this with the polishing contractor and the reactive chemicals. A slab with more than a 7-pound water vapor emission problem can form visible efflorescence at the surface overnight or over a weekend. Unfortunately treatments and cleaners that dissolve the alkali deposits can also harm the polished concrete surface.

A pH what?

During my 30 years of work in the industry, I can count on one hand the number of specialty floor contractors I encountered with a pH test kit. The test kit contains $12 in litmus paper and a small container of distilled water. I didn’t witness someone using a pH test on a concrete floor until acid stains were prevalent. This was the only way to know if the acid in the stain was properly neutralized for the installation of the sealer.

Quite simply, a pH test is a highly revealing check and can be completed in five minutes. If pH at the surface is high, (10 or higher) it can indicate a water vapor emission problem. Concrete dyes, which are powders that are homogenized into a dissipating liquid for delivery and penetration, are pushed to the surface by high water vapor emissions. This causes the dye to loosen and lift from the surface. When it comes to acid stains the opposite may be true. These chemicals depend on a high pH because the colors are produced by the reaction of the metallic salts in the acid stain and the hydrated lime, or calcium hydroxide, which is a by-product of cement hydration in the concrete. In either case, the key is to know what the conditions are before work starts.