How do Ottawa contractors test for moisture in concrete before applying epoxy

Moisture Testing Methods Ottawa Epoxy Contractors Use Before Coating

Professional epoxy contractors in Ottawa rely on two primary moisture testing methods before applying any floor coating: the calcium chloride test (ASTM F1869) and the relative humidity probe test (ASTM F2170). Both are essential in Ottawa because our extreme climate — with over 200 centimetres of annual snowfall, spring melt, and a high water table in many neighbourhoods — drives significant moisture vapour through concrete slabs year-round.

The calcium chloride test involves taping a small dish of calcium chloride crystals to the cleaned concrete surface under a sealed plastic dome. After 60 to 72 hours, the dish is weighed to determine how much moisture it absorbed. The result is expressed as pounds of moisture vapour emission per 1,000 square feet per 24 hours. Most professional epoxy systems require a reading below 3 pounds, though some high-performance moisture-mitigating primers can tolerate up to 5 pounds. This test is affordable, typically running $75 to $150 per test location in Ottawa, and most contractors will test at least two or three spots across a garage or basement floor.

The relative humidity (RH) probe test is considered the more accurate of the two methods. A contractor drills small holes into the slab at 40 percent of the slab depth, inserts calibrated humidity probes, and allows them to equilibrate for at least 72 hours. The reading must typically fall below 75 percent relative humidity for standard epoxy systems. This method captures a more complete picture of moisture conditions within the slab rather than just the surface, which is particularly important in Ottawa where seasonal moisture fluctuations can vary dramatically between spring and late summer.

Many Ottawa contractors also perform a simple plastic sheet test as a preliminary screening. They tape a two-foot-square piece of clear polyethylene to the floor for 24 to 48 hours and check for condensation or darkening underneath. While this is not a quantitative test and cannot replace calcium chloride or RH probes, it quickly reveals whether moisture is obviously present. If condensation appears, the contractor knows more rigorous testing is essential before proceeding.

In homes built before the 1980s — common in neighbourhoods like the Glebe, Old Ottawa South, and Sandy Hill — there is often no vapour barrier beneath the slab, making moisture testing even more critical. Newer builds in Barrhaven, Kanata, and Riverside South typically have poly sheeting under the concrete, but even these can develop moisture issues due to Ottawa's Leda clay soil and seasonal water table fluctuations. A reputable contractor will never skip moisture testing regardless of the home's age, and the $150 to $400 investment in proper testing can save thousands in coating failure and reapplication costs down the road. You can browse flooring contractors who perform pre-installation 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:

• Homeupgraders
• RenoMotion Inc.
• PLD Residential Renovations Inc.
• HAflooring
• Ottawa Caulking