Controlling moisture levels is a vital aspect of construction and building maintenance. Excessive water in concrete slabs can lead to mold growth, adhesive problems, and severe structural issues when left unchecked. The calcium chloride test emerged in the early 1940s as a preliminary method for assessing moisture in concrete slabs. Today, it is a widely available, trusted technique used by millions of construction experts worldwide.
In this blog, we’ll explore the calcium chloride test’s significance, applications, and benefits. We’ll also discuss how to perform a calcium chloride test yourself and reveal where you can find the best equipment to do the job accurately and reliably every single time.
What is the calcium chloride test?
Calcium chloride moisture tests, also known as the ASTM F1869 standard test method, are a simple, effective way to assess the moisture vapor emission rate (MVER) of a concrete slab. In short, it shows how much moisture is in concrete, allowing us to evaluate the material’s properties and assess its viability for its intended purpose.
The calcium chloride test works on the principle that calcium chloride is a highly hygroscopic material, meaning it absorbs water like a sponge. This absorbency means the calcium chloride will soak up water vapor from the concrete slab, causing a weight increase in the sample. We can then use the difference between the start and end weight of the calcium chloride to calculate the amount of moisture in the concrete.
Why does moisture content in concrete matter?
Moisture is both the closest friend and worst enemy of concrete. It is a necessary component of every concrete mix, ensuring flexibility, workability, and flowability. That said, too much moisture can be detrimental to the stability and performance of the end product. A higher water content typically makes concrete weaker and more permeable.
A high moisture content can also cause cracks in the concrete, affecting durability. Freeze-thaw cycling and internal ice formation will cause the concrete to expand, creating fissures that contribute to the degradation of the material.
Assessing the moisture vapor emitted from a concrete slab indicates the mixture’s properties, allowing construction experts to make informed decisions about the quality and longevity of concrete flooring.
Concrete moisture also greatly impacts the effectiveness of flooring installation. Too much moisture vapor evaporating from a concrete surface can cause significant problems when applying coatings or flooring adhesives. It can also cause the flooring to buckle, warp, and change shape.
Finally, moisture in concrete can contribute to the growth of efflorescence (white salt deposits), mold, and mildew, which can create serious health hazards, especially if the flooring installer is working in an indoor area.
Why is it important to assess concrete moisture?
Now that we’ve discussed the impact of excess moisture in concrete, let’s discuss some of the key reasons why we need to test for it.
Assessing flooring suitability: Assessing the moisture content of concrete gives construction experts confidence that their project will go to plan. It allows them to assess concrete suitability and check that the floor covering materials they intend to install will work as intended.
Preventing structural failures: Concrete moisture can lead to many structural problems in the long term, such as adhesive bond failures, warping, buckling, and mold. The calcium chloride test identifies potential problems early, enabling floor covering industry professionals to address issues before they worsen.
Meeting industry standards: Many industries have established guidelines in place regarding acceptable concrete moisture levels. The calcium chloride test is a fundamental step toward meeting the rigid standards in place for construction professionals.
Reducing costs: Understanding the moisture content of a concrete slab helps reduce the cost of expensive repairs. Discovering a problem in a concrete slab enables the construction expert to take preventative measures, reducing the likelihood of reinstallation in the future.
Keep Reading: Complete Water Quality Testing Guide: How and Why.
How do you perform a calcium chloride test?
To better understand how the calcium chloride test works, let’s discuss how to perform one.
You will need:
Calcium chloride moisture test kits
A scraper or wire brush
A thermometer
A gram scale
Safety equipment (Gloves, goggles, masks)
Performing a calcium chloride test: step by step
Follow these simple steps to perform simple, accurate calcium chloride tests each and every time.
Assess environmental conditions: For accurate results, ensure that the building you’re testing in is between 65°F and 85°F with a relative humidity of 40-60% as per the ASTM F1869 standard. These conditions establish a moisture vapor equilibrium, standardize the test and optimize moisture absorption rates.
Gather your equipment: Collect all necessary materials, including calcium chloride moisture test kits, a wire brushes, thermometers, safety equipment, and your scale.
Prepare the concrete: Use a scraper and wire brush to thoroughly clean the concrete slab. Ensure you remove any dust, dirt, and loose particles that could impact the accuracy of your results. Never use chemicals to clean the floor. Aim to clear a minimum 20×20 inch surface area before testing.
Prepare the calcium chloride: Remove the sealed calcium chloride dish and weigh it to the nearest 1/10g. Keep the calcium chloride in the dish when weighing, as this will make it easier to record the weight difference later. Be sure not to spill any of the calcium chloride, as this will make your test inaccurate.
Apply the test kits: Remove the protective sticker from your test kits to expose the adhesive side. Place the test kit on the concrete surface and press firmly. Position 3 test kits for areas up to 1000ft², and add one extra test kit for each additional 1000ft².
Place the calcium chloride dish: Remove the lid from each pre-weighed calcium chloride dish and place them in the center of your test areas.
Seal the test kits: Seal the calcium chloride test kits using the plastic dome included in your test kit. Peel off the protective film and place the dome over the dish, pushing down to make the test environment airtight.
Wait for the recommended time: Allow the test to remain undisturbed for 60 to 72 hours. The exact duration required will depend on the manufacturer of your test kit. Ensure the dome is not exposed to sunlight during this period.
Weigh the dish: Remove the plastic dome cover from your sample. Reseal the calcium chloride dish and weigh it using the same scale you used at the beginning of the test. Record the final weight, date, time, and test location. Remove the adhesive from the concrete surface.
How do you calculate the moisture vapor emission rate?
Now that you’ve completed your experiment, it’s time to calculate the final result. MVER is measured in pounds of moisture emitted per 1,000 square feet over 24 hours (lb/1,000 ft²/24 hours).
The formula for MVER will depend on the testing standard and kit you use. For this example, we’ll base our calculation on the Gilson HM-674D Concrete Moisture Emission Test Kit. The formula for calculating MVER using this kit is:
(52.91 x M) ÷ (A x T) = MVER
M = Mass increase between the final sample and initial sample
A = Contact area of test minus area of the dish (most test kits will specify a nominal value)
T = Test Duration
To better understand how this works in practice, let’s assume your experiment achieved these results:
M (Mass increase) = 5.0g
T (Duration of test) = 72 hours
A (Contact area of test minus area of dish) = 0.52ft²
Let’s put these measurements into our formula:
(52.91 x M) ÷ (A x T) = (52.91 x 5) ÷ (0.52 x 72)
52.91 x 5 = 264.55
0.52 x 37.44 = 24.96
264.55 ÷ 37.44 = 7.065
MVER = 7.065
An acceptable emission rate for concrete is typically considered to be 3 pounds or 5 pounds depending on the standard. This test result would indicate that the MVER is too high, making the concrete unsuitable for flooring applications.
Calcium chloride moisture test vs relative humidity test: which is better?
Like the calcium chloride test, relative humidity testing (RH) is a method used to measure the moisture content within a concrete slab.
The test involves inserting an RH probe into a hole drilled into the concrete surface. The probe contains sensors that measure the temperature and RH of the air inside the hole. After 24 to 72 hours, the tester can read a meter connected to the probe to measure RH, revealing the moisture conditions within the concrete slab.
RH testing has some clear advantages over calcium chloride moisture testing. Firstly, RH tests can be more accurate and reliable because the probe penetrates deeper into concrete floors. In contrast, the calcium chloride test only measures the upper few inches of the concrete.
In addition, the RH test gives readings in-situ, and can be left in place for extended periods, allowing for continuous monitoring of concrete over time. The calcium chloride test must be removed and weighed after each test.
That said, RH testing is considerably more expensive than calcium chloride tests, so they aren’t suitable for everyone. The right choice for you will depend on your budget and testing applications.
Where can I find the best concrete moisture testing equipment?
The first step to consistent, reliable calcium chloride tests is choosing the best-quality equipment.
CertifiedMTP stocks a wide range of first-class concrete moisture testing equipment. From calcium chloride kits and environmental meters to relative humidity test kits and pH test strips, we have the high-quality tools you need to get accurate moisture readings time and time again.
Looking for something different? We also offer a wide range of soil moisture testing and aggregate moisture testing equipment. Whatever your material testing needs, CertifiedMTP has the equipment you need to get the job done.
Still can’t find the equipment you’re looking for? Don’t hesitate to reach out. We’re always happy to help you find the right tools for your material testing needs.
