When solid concrete floors, soil, and aggregates go from stable and sturdy to fragile and insecure, moisture is often the culprit. Moisture damage can go unnoticed by the naked eye until it’s too late. Water dripping from walls, cracks forming in concrete, and soil becoming unstable are all unfortunate times to realize your materials contains more moisture than they should. Accurate moisture testing is essential to ensure all structures are solid and safe for the long term.
There is no defined, standard test method for moisture testing. Every situation is different – the technique used depends on the material, location, and situation.
In this article, we’ll discuss some of the best methods for testing moisture in materials, including benefits, drawbacks, and the equipment needed to perform tests accurately.
8 Common Moisture Testing Methods
In this section, we’ll focus on 9 common types of moisture testing used for concrete, soil, and aggregate testing applications.
Moisture testing in concrete floors, also known as testing concrete moisture, is crucial to prevent issues such as mold and material degradation, ensuring the durability and performance of concrete structures.
1.  The Karl Fischer titration test (KF)
Originally invented by the chemist Karl Fischer, this moisture meter test relies on a chemical reaction to achieve measurable results.
During the test, the researcher dissolves the test material into a solvent. They then mix this solvent with a specific chemical reagent that reacts with water. This reaction separates the liquid in the sample from the material, enabling accurate measurement.
The Karl Fischer test provides a highly accurate reading, measuring samples to parts per million (ppm). For this reason, chemists typically use it to measure samples with trace amounts of water.
That said, there are some drawbacks to the test. The method is destructive, as it alters the test sample. This can be a problem if the sample is important or expensive. The KF test also requires a high level of expertise and can be time-consuming.
There are two ways to perform the Karl Fischer test; these are the volumetric KF test and the coulometric KF test.
Volumetric KF test
In the volumetric KF test, a researcher adds a known quantity of a reagent to a sample within a volumetric titrator. The reagent then binds with water molecules in the solution. Researchers determine the amount of moisture by measuring how much of the reagent was required to complete the reaction.
Coulometric KF test
In the coulometric KF test, the tester combines the reagent and sample by inducing an electrochemical in a coulometric titration cell. The amount of current required to convert the water and end the reaction is used to determine the amount of moisture present in the sample. The coulometric test is more accurate than the volumetric test, meaning researchers typically use it to measure smaller quantities of water.
The Anhydrous Calcium Chloride Test
Some reagents, such as calcium carbide, emit gas when they react with moisture. The amount of gas the calcium carbide releases indicates the moisture present in the sample.
The calcium carbide method is simple and rapid, making it an excellent option for on-site testing of concrete floor slabs, concrete walls, soils, or aggregates. This method is also applicable for testing moisture levels in a concrete subfloor, which is crucial for ensuring the integrity of flooring installations. However, it is not as precise or reliable as the Karl Fischer test, so it isn’t suitable for laboratory-based tests requiring precise accuracy.
The calcium chloride test, also known as the moisture vapor emission rate (MVER) test, is a simple, affordable method for testing the relative humidity of concrete, soil, or aggregates.
During the test, a researcher places a container filled with a known quantity of anhydrous calcium chloride on the test surface, as described in ASTM F1869. The tester then covers the sample and leaves it for 24-72 hours to allow the anhydrous calcium chloride to absorb water vapor emitted from the substance. The calcium chloride crystals are then weighed. The difference between the start and end weight of the anhydrous calcium chloride shows the relative humidity of the sample.
Like the calcium carbide method, the calcium chloride test is excellent for on-site, in-situ measurements. However, it is not a reliable substitute for more accurate tests like the Karl Fischer method.
3.  Oven-Dry Testing
The oven-drying moisture test is a simple procedure used to determine concrete, soil, wood, and aggregate moisture content. It involves placing a sample into a controlled, calibrated oven and dehydrating it at a specified temperature until it reaches a constant weight. The weight difference between the original and new samples indicates the excess moisture that has evaporated from the substance. The oven-dry testing method is also used as a concrete moisture test to assess moisture levels in concrete.
Although oven-dry testing is a reliable and accurate method for testing samples of materials, it is time-consuming and, therefore, unsuitable for those who require instant results. It is also destructive, as the test alters the sample beyond its original state.
4.  Nuclear Testing
Nuclear density testing is a fast, non-destructive method of determining the in situ moisture content of aggregates and soils. The researcher uses a nuclear gauge to pass beta radiation through the sample. The particles react with the sample’s water content, and the resulting radiation levels accurately reveal the moisture level of the substance. Nuclear testing typically requires up to 20 samples to be accurately calibrated.
Nuclear testing is quick and non-destructive. The method also provides results in real time. However, it requires high-quality, specialized equipment and lots of expertise, making it a challenging method for inexperienced researchers.
5.  Electrical moisture testing
Certain moisture meters, such as the C555 Moisture Meter, test the moisture content of concrete slabs using electromagnetic waves. This method is particularly useful for ensuring that the concrete is dry enough for the installation of any floor covering, thereby preventing issues such as flooring failure and mold. The waves pass through the concrete and are subsequently reflected back to the meter. Researchers can then analyze the results to determine the moisture content of the material.
This non-destructive concrete testing method quickly and reliably tests wood, flooring, and concrete moisture. It benefits construction experts. Yet, electrical testing might only provide surface-level readings. It’s influenced by temperature and humidity. This method assesses moisture levels in concrete surfaces, key for coating applications.
6.  ASTM F2170
The ASTM F2170 technique tests concrete moisture by measuring in-situ relative humidity (RH). It requires drilling a hole in the concrete slab and inserting a probe. This probe measures RH at a specific depth. Researchers leave the probe in place for 24-72 hours for an accurate reading. ASTM F2170 is a method in various ASTM standards.
The ASTM F2170 testing method is a helpful way for researchers to assess the suitability of concrete as a building material, making it a key testing application in the construction industry.
7.  Near-infrared testing (NIR)
The near-infrared test involves using a spectrophotometer to fire a beam of infrared light at the sample material. The light interacts with the chemical bonds in the substance. The spectrophotometer then measures the resulting reflection and absorption to determine the amount of moisture present. The more infrared light the sample absorbs, the more water it contains.
The main disadvantage to NIR is that infrared light rarely penetrates through the whole material. If a material has a coating, the light will reflect back off of the surface, providing an inaccurate reading.
8.  Time domain reflectometry method (TDR)
In this method, a probe is inserted into the material being tested. The researcher then transmits a high-frequency signal through the probe. The time it takes for the signal to reflect from the water in the material indicates the sample’s moisture content.
TDR is reliable, accurate, and non-destructive. However, it’s expensive and needs precise calibration based on material type. This makes it challenging for inexperienced researchers. Where can I find moisture testing equipment?
Certified MTP is the one-stop shop for all of your material testing needs. We have a wide range of moisture test equipment, all designed for efficiency and rigorously tested for accuracy.
From concrete testing methods to soil and aggregate equipment, our range of moisture testing tools are custom-built to help you get the job done right first time, every single time.
Looking for something in particular? Get in touch today. Our qualified team of experts is always happy to help you find the testing tool to suit your needs.
