What is a calcium chloride moisture test?
A calcium chloride moisture test measures moisture vapor emission from concrete slabs in pounds per 1,000 square feet over 24 hours, used to determine if a slab is dry enough for flooring or coating installation.
The calcium chloride moisture test determines how much water vapor a concrete slab is releasing into the air. A technician places a calcium chloride powder in a sealed dome on the concrete surface for 24 hours. The powder absorbs moisture from the slab. After 24 hours, the dome is removed and the powder is weighed to calculate moisture vapor emission rate, reported in pounds per 1,000 square feet per 24 hours (lb/1,000 sq ft/24 hr).
This test is required before installing epoxy and other moisture-sensitive flooring systems over concrete. If moisture vapor transmission is too high, coatings and floor materials can bubble, peel, or fail within months. Most epoxy installations require results below 3 to 5 lb/1,000 sq ft/24 hr, depending on the product specification. Connecticut contractors performing slab work must verify moisture levels meet manufacturer requirements before installation begins. The test serves as proof of slab readiness and protects against premature floor failure.