September 17/24, 2018: Volume 34, Issue 7
By Marlene Morin
It’s a given that a high content of moisture in a concrete slab will damage a floor. But where does the moisture come from? How can it be tested and measured? More importantly, how do you solve a moisture issue?
Following are a few answers to these critical questions.
Where does moisture come from? Concrete is made of five elements: cement, sand, aggregate, air and water. Water is used to help the chemical reaction between the different elements and support the workability and the placement of the concrete. The latter takes between four to six months to evaporate, while other sources of moisture can then influence the concrete that was poured. Moisture can come from below grade, earth or water table, to name a few.
Testing the moisture content. Each floor covering you intend to put down can handle a certain amount of moisture. This limitation is given by the manufacturer and varies from one floor to the other.
Understanding moisture limitation will help you avoid mold and bacteria, blistering, delamination, swelling and debonding.
How to measure moisture content. There are five ways recognized by the American Society for Testing and Materials (ASTM) to measure the moisture content. Two of the ways produce qualitative measurements and tell you if there is a moisture issue. The other three ways are quantitative and tell you the amount of moisture content.
The qualitative methods include the plastic sheet test (ASTM D4263) and concrete surface pH testing (ASTM F710). You can also use the mat bond test to identify if there is a moisture issue, but there is no ASTM standard for this.
The quantitative methods are the MVER test, also known as the calcium chloride test (ASTM F1869), the relative humidity test (ASTM F2170) and the electrical impedance test (ASTM F2659).
I recommend performing a quantitative test. You can easily compare the amount of moisture content to the moisture limitation of your floor and decide if you have to treat the substrate prior to application.
How to solve a moisture issue. Now that you have identified a moisture issue, you have to mitigate the moisture to avoid further problems.
There are different types of moisture mitigation solutions. The reactive penetrants products will react with the chemical inside the slab to reduce the porosity of the concrete and reduce moisture transfer. In order for the products to perform, it is important to know if there are enough possible chemical reactions within the concrete.
You can also use high-performance adhesives. However, you need to make sure the concrete is in great shape and check what “high performance” means. Be sure to read the moisture limitation.
For wood floors, you can use an all-in-one adhesive. The chemistry behind these adhesives allows you to glue down your wood while preventing the moisture in the slab to escape. This solution is a great alternative when you are gluing down engineered wood floors.
And last but not least, you can use epoxy solutions. These products offer a very high level of moisture protection and are usually easy to apply.
Marlene Morin is a marketing manager at Sika Corp. In this capacity, she oversees the marketing activity of the floor covering division of Sika USA. Morin is also a certified ICRI Concrete Slab Moisture Technician.
