Technical Focus: 4 Ugly Consequences of Excess Concrete Moisture
Excess moisture from concrete subfloors can cause serious problems with all types of flooring. These range from aesthetic problems to health and safety hazards.
Here are four ugly consequences when moisture is trapped beneath a flooring system:
- Adhesive degradation
- Coating debonding
- Osmotic blistering
- Microbial attack
Adhesive degradation occurs when a moisture-sensitive adhesive breaks down from exposure to too much alkalinity. Excessive moisture allows alkaline materials to move to the top of the slab, where it can attack the concrete. This moisture allows the very basic makeup of concrete to attack the adhesive. The adhesive might begin to ooze from the seams and the floor might lose its bond with the floor. Other problems include epoxy and resin floor coatings debonding from the concrete. Coatings can also develop osmotic blisters.
A microbial attack can also be a serious health concern. Howard Kanare, concrete moisture expert and author of Concrete Floors and Moisture, writes, “Excessive moisture trapped under floor finishes can create conditions for mold and mildew to grow. When flooring is removed, blooms of fungal spores can become airborne, and may cause allergic reactions or respiratory problems.”
All of these problems are caused by too much moisture in a concrete subfloor. That means you must determine whether the concrete is dry enough before you install a floor over it.
All concrete contains moisture and a certain amount is not a problem. But, when there’s too much moisture, it becomes a medium to allow the alkalinity to move up through “capillaries” in the concrete to attack the adhesive at the surface.
As water evaporates, water from deeper in the concrete moves through the concrete’s pores to the surface to replace it. Since water evaporates from the surface of the concrete, the surface is usually drier than the concrete deeper in the slab. So even if the slab looks dry, eventually much of the water deep in the slab will make its way to the surface. As the water collects under the flooring system installed on the slab, it brings serious problems with it.
So just looking at the slab isn’t enough to know if it’s dry. Using a test on the slab surface isn’t enough either. Only a test that can detect moisture deep in the center of the slab will be reliable.
Concrete moisture testing has been studied since the 1960s, and researchers have developed a scientifically proven test for measuring moisture levels deep in the center of a slab.
This test requires sensors for measuring the relative humidity (RH) of the air trapped in the concrete. These sensors are inserted into the slab at specific depths for accuracy. This has been determined to be the best way to get an accurate picture of how much moisture lies deep within the slab.
This test is called “the relative humidity test using in situ probes,” and it’s the basis for the ASTM F2170 standard.
Monitoring ambient conditions
With new construction involving a flooring system over a concrete slab, the concrete drying process is usually the critical path. Constant monitoring of the slab’s moisture condition can help you to make a better estimate of when drying will be complete, so you can schedule dependent tasks earlier.
Ambient RH, the temperature of the air and air movement are important factors in determining how fast concrete dries. That means it pays to monitor ambient conditions during the drying period. Monitoring ambient temperature and RH enables you to spot drying problems early and correct them so that you can shorten drying times and better estimate completion times.
To help you monitor, record and report ambient conditions, Wagner Meters introduced the Smart Logger, a small battery powered data logger that can record ambient temperature and RH for 300 days of replaceable battery life or up to 12,000 readings. The Smart Logger transmits data via Bluetooth to the Smart Logger app running on any iOS or Android device. The app allows you to generate, print and email reports.
Visit the International Concrete Repair Institute’s website at www.icri.org for more information on the next steps or to find an expert to help.