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Jan 20, 2017 | Concrete Repair, Moisture Problems, Moisture Testing | 0 comments

Do you have a concrete slab that is in need of moisture sensitive coat­ing? Have you done your research and found an abundance of confusing information? Did you get varying information on which test to do first? Have you asked yourself these questions? Are they necessary? How do I make sense out of all this information?  We can certainly clarify some of this information for you.Flooring

To answer your question about moisture testing we say that yes! Testing is necessary. It is said that moisture related flooring failures cost hundreds of millions of dollars annually.  A study that was conducted in 2005 reported that more than 80 percent of new and re­modeled/adaptive reuse floors never get tested for moisture. These facts alone justify the need for moisture testing.

The most confusing part of moisture testing is knowing when and how to test. There are various testing products ranging in prices, from cheap and quick to pricey and invasive. Each test will result in suitable results but each one tells you something different about the moisture level in the concrete.

Most moisture meters’ function on the principles of electrical impedance, radio frequency, or electrical conductivity/resistance. Generally, relative mois­ture content can be checked by placing two contacts on the concrete, pushing a button, then converting the reading signal to a relative moisture measurement.

What do I do first?

Begin your testing process by mapping the slab. This is to familiarize yourself with areas where the slab appears wet, dry and in-between. Mapping ensures that you will use the right number of tests for your concrete slab. Moisture meters are used to map problem areas. Moisture meter checks only takes a few seconds.

Begin the testing process by walking the entire floor with the meter and getting a snapshot of the relative readings throughout the floor. Ensure that doorways, the middle of the slab, where pipes are buried, areas where there’s airflow and sunlight on the floor, are all checked. To ensure accuracy check every few feet

Which Test Should I Use?

After this process is done you can proceed to more specific moisture tests. Which tests should you use? Many contractors use the F2170 moisture test. These contractors often go out business after completing one or two concrete flooring jobs. The F2170 and similar tests don’t give precise num­bers on moisture content. Just seeing a result of moisture content below 50 on the moisture meter scale of 0 to 100, doesn’t mean that the reading is good in terms of absolute mois­ture in the concrete. Continuing a flooring job on the results of these types of test isn’t much different than not testing at all.


The following tests are commonly used:

  • The ASTM F1869 standard test method for measuring moisture vapor emission rate of concrete subfloor using anhy­drous calcium chloride. This test is used to find out exactly how much moisture is coming through the floor. The ASTM F1869 is more Commonly called the calcium chloride test. To test you place a dish of calcium chloride under an airtight dome on the concrete for 72 hours. Then, weigh the dish. This test is measured in pounds of water emitted from 1,000 square feet. These results will be used to show how likely your coating will fail because of water vapor. Flooring manufacturers recommend a maximum rate of 3 pounds per 1,000 square feet.
  • The plastic sheet moisture testing method involves duct­ taping an 18 square-inch sheet of clear plastic to the floor and leav­ing it for 16 to 24 hours. If there’s condensation in-between the plastic and the concrete, you’ve got moisture.
  • The ASTM F2170 Standard Test Method, is used to determine relative humidity in concrete floor slabs using in situ Probes. Situ Probes are common for moisture testing. They require drilling holes in the floor to 40 percent of the slab thickness. This method demands three test locations on the concrete slab up to 1,000 square feet (93 square me­ters). One test is required for each additional 1,000 square feet. If you’ve got a big slab this test would require a lot of holes and additional tests which are quite expensive.
  • Electronic moisture meters and the ASTM D4263 Standard Testing Method for Indicating Moisture in Concrete by the Plastic Sheet Method are easy and cheap.

How do I test?

The problem with moisture testing is that you can have dry concrete for the first inch or so, with more moisture deeper down. Installing the floor­ing traps the moisture at the surface as it gradually rises, until the first few inches of the slab is all wet causing prob­lems. Accurate testing kits are expensive, but since you’ve mapped the areas of moisture in the floor, you should have a better idea of how many you need.

You should test areas of wet, dry and in-between. The moisture tests only measure moisture con­tent of the surface. To test deep within the slab, contractors often use a modified version of ASTM F1869. This test allows you to see how moisture will redistribute after the flooring installation.

The modified ASTM F1869 test involves sim­ulating the floor coating by taping down plastic sheeting or other vapor-impermeable material, and leaving it for few days. After the incubation period cut a hole in the material and run the ASTM F1869 test as well as the standard F1869 test where the floor was not covered. This process can reveal issues such as os­motic blistering.

This process gives you similar results to the ASTM F2170 Standard Test Method, which is used to determine relative humidity in concrete floor slabs using in situ Probes. Do you need it to perform this test if you’ve already run F1869 and its modified cousin? To answer that question, you must ask yourself three more questions.

  1. How moisture-sensitive is the flooring?
  2. How critical is it to you that the flooring doesn’t fail?
  3. And Lastly, as Clint Eastwood asked in “Dirty Harry”, do you feel lucky?

Drilling holes and insert­ing probes in areas identified as prob­lematic tells you how much and how deep the moisture is in the floor.

The ASTM F2170 test determines the relative hu­midity of the concrete slab at a specific depth. A hole is drilled into the slab to a predetermined depth. The hole then gets a sleeve and a probe inserted into the sleeve for a reading. This method is more accurate than F1869 test because it requires a depth of 40 % of the slab thickness. The test results indicate the potential moisture reservoir and vapor emission rate within the concrete slab. The sleeves and probes can be left in the concrete if they are monitored. Concrete reinforced with metal fibers can produce false readings.  The recommended percentage of humidity before applying the flooring system is 75 per­cent or less.

Avoid Problems

On occasion the tests may indicate that moisture is not the issue. This means that the floor can be installed with a high probability of success. On the other hand, the tests may indicate that the moisture level is a problem. In this instance, there are a few things you can try to bring down the humidity in the slab including setting up dehumidifyers, a mitigation system, or installing a minimal moisture-sensitive flooring.

The only way to ensure successful installation of concrete floor coating is to follow a testing hierar­chy from the initial visual survey to the F2170 test. Each test has its value and its place in the hierarchy, and the tests referenced here are not the only ones. To get an idea of the slab’s moisture condition test systematically, map out general problem areas with qualitative tests and then definitively test those problem areas with more quantitative methods.

When these steps are followed, you have the actionable information you need to keep your floor and your character from being drenched.

Does that sound easy enough? If you need someone to give you a certified third party moisture test, Concrete Fusion can help. Visit our website or call us (613) 714-0656

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