The Test Most Contractors Skip Entirely

What Moisture Vapor Emission Actually Is

Concrete slabs sit on soil and are naturally porous at a microscopic level, so water vapor from the ground constantly moves up through the slab, at a rate that varies by season, soil type, and whether a vapor barrier exists underneath. Florida's clay-heavy soils and freeze-thaw cycle make this a more relevant factor here than in drier climates.

Why It Matters for Coating

A coating essentially seals the top of the slab. If vapor is emitting at a rate the coating system can't handle, pressure can build beneath that sealed surface over time — showing up as bubbling, delamination, or a milky white haze under the coating known as osmotic blistering. This sometimes doesn't appear until months after an install that looked perfectly successful on day one.

How We Test Every Slab

We run a calcium chloride test or a relative humidity (RH) probe test on-site before quoting the job, measuring the slab's actual emission rate against the coating manufacturer's maximum tolerance for that specific product.

Why Most Contractors and All DIY Kits Skip This

The test itself takes time — a calcium chloride test typically needs 60–72 hours to read accurately, or several hours for an RH probe reading — and equipment most budget contractors simply don't own. Skipping it doesn't cause an immediate problem, which is exactly why it gets skipped. The failure shows up months or years later, by which point the installer is long gone.

What Happens If a Slab Tests High

It isn't a dealbreaker. A high-emission slab can still be coated using a moisture-mitigating primer system rated for that specific vapor pressure. The point of testing isn't to disqualify a job — it's to install the correct system for that particular slab instead of guessing.