What is a calcium chloride moisture test and do Ottawa contractors use them

Understanding the Calcium Chloride Moisture Test for Ottawa Epoxy Projects

A calcium chloride moisture test — formally known as ASTM F1869 — is the most widely used method for measuring moisture vapour emission from concrete slabs before applying epoxy or other floor coatings. Yes, Ottawa contractors use them extensively, and any reputable epoxy flooring professional in the region should include this test (or its companion RH probe test) as a standard part of their pre-installation assessment. Given Ottawa's extreme moisture conditions — spring snowmelt, high water tables, and Leda clay soil — skipping this test is one of the fastest ways to guarantee an expensive coating failure.

The test works by measuring how much moisture vapour is being emitted from the concrete surface over a set period. A contractor places a pre-weighed dish of anhydrous calcium chloride (a highly absorbent salt) on a cleaned section of concrete and seals it under a plastic dome with airtight tape around the edges. The dish sits undisturbed for 60 to 72 hours, during which it absorbs moisture vapour coming through the slab. After the test period, the dish is reweighed, and the weight gain is calculated to determine the moisture vapour emission rate (MVER), expressed as pounds of moisture per 1,000 square feet per 24 hours.

For most epoxy and polyaspartic coating systems, the maximum acceptable MVER is 3 pounds per 1,000 square feet per 24 hours. Some moisture-tolerant primers can handle up to 5 pounds, and specialized moisture vapour barriers are rated for 15 to 25 pounds. In Ottawa, spring readings commonly range from 4 to 8 pounds in older homes without sub-slab vapour barriers, while newer construction with proper poly sheeting typically reads 1.5 to 3.5 pounds. A professional contractor will test at minimum two to three locations across the floor to get an accurate picture, since moisture levels can vary significantly across a single slab.

The cost of calcium chloride testing in Ottawa runs $75 to $150 per test location, or roughly $200 to $400 total for a typical garage or basement with two to three test points. Many contractors include this cost in their overall quote, while others list it as a separate line item. Either way, it is a small fraction of the total project cost — typically less than 5 percent — and provides critical information that determines whether the floor needs a moisture barrier, whether the project should proceed immediately or wait for drier conditions, and which coating system is appropriate.

One important limitation of the calcium chloride test is that it only measures surface moisture emission, not the moisture condition deeper within the slab. For a more complete picture, some Ottawa contractors also use relative humidity (RH) probe testing (ASTM F2170), which involves drilling into the slab and measuring humidity at 40 percent of the slab depth. The RH probe test is considered more accurate for predicting long-term coating performance, but it costs slightly more and requires drilling holes in the concrete. Many Ottawa professionals now offer both tests or have moved primarily to RH probes, especially for high-value basement projects. When comparing quotes, ask whether moisture testing is included and which method will be used. You can find flooring contractors who perform proper moisture assessments through the Ottawa Construction Network directory at justynrookcontracting.com.

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Looking for experienced contractors? The Ottawa Construction Network connects Ottawa homeowners with qualified professionals:

• Justyn Rook Contracting
• JC Carpentry
• Geerts Roofing Inc
• Custom By Arie
• Kitchens by Michael o/a Michael Francis Home Improvements