One of the first things I do when I arrive on a estimate is to test the concrete for moisture. It’s important to have an idea just how much moisture is in the slab in order to feel comfortable offering an extensive warranty. We will discuss the methods and tools available to you. I will also reveal to you my preferred methods of quickly and effortlessly testing all slabs for moisture.
There have typically been three major types of tests for measuring concrete moisture. Each one has a specific use that may or may not be best suited to monitoring a concrete slab. Some might be overkill for a residential garage floor installer.
Calcium Chloride Kits
The calcium chloride test method is used to determine the moisture vapor emission rate from a concrete slab. Calcium chloride testing involves taping a small dish of calcium chloride on a clean section of concrete under a plastic dome. These kits have been used for quite some time now, but be aware that they produce unreliable results. They only measure moisture migration at a very shallow depth. Testing shallow depths is covered by ASTM F1869, but the standard has been amended to exclude calcium chloride as an acceptable test method for lightweight concrete. You will see some plans still spec out calcium chloride kits. However commercial installers should be aware that this will not meet ASTM requirements. Not something residential garage floor installers need to worry about.
Hand-Held Concrete Moisture Meters
This is a non-destructive method of quickly testing the concrete for moisture. It does it by way of electrical impedance which can vary in proportion to the moisture in the slab. The electrical impedance is measured by creating a low frequency alternating electric field (AC) between each electrode. These are a valid general survey tool, but they do not read deep enough to detect a slabs true moisture content. Hand-held electromagnetic fields only penetrate about one inch into the slab. They can also interact with the steel rebar in the concrete to give a false reading of the moisture conditions. For commercial installers a hand-held moisture meters is just one peice of the puzzle to test concrete. It cannot be reliably used alone to determine when to install a floor covering.
Relative Humidity (RH) Testing
This a more intrusive way of testing, but also the prefered way for most commercial contractors. They will use this method along with a moisture meter such as the one previously described. This test is conducted by drilling holes in the slab and inserting “in-situ” probes which measure RH deep within the slab. Their depth-specific application has proven to accurately represent moisture conditions. Since they are located deep in the slab they are less susceptible to environmental or ambient changes at the surface.
My Preferred Method Of Testing The Concrete Slab For Moisture
The method I prefer to use is the moisture meter testing method. Its extremely fast and provides a good idea of what is going on in the slab. I have Tramex CME4 that I keep with me at all times. When testing in front of homeowners I always hear, “that nice, the other companies didn’t run a test”.
It helps to provide me with a level of comfort for as well as to provide the customer with and option to re-mediate the issue with a vapor lock. If they decide to opt out of the vapor lock then I do not have to warranty it. Sure I have done some commercial work in the past but it has been smaller types of commercial projects about 2000-3000 square feet. I used this method for that as well. However I think I would not feel comfortable with this test method on a 20,000 square foot install.