Key takeaways
- Every slab on the ground carries vapor
- Testing is quick and cheap insurance
- Primers handle many moderate cases
- Fix water sources before coating
How moisture gets through
Concrete is porous, and a slab on the ground is in constant contact with soil moisture. Vapor rises through it all the time, even when the surface looks dry. Seasonal humidity, rain and the water table change how much.
A coating seals the surface, so vapor that used to evaporate gets trapped, and that pressure is a common cause of blisters and peeling.
How to test
Several tests exist. A calcium chloride test measures vapor emission over a set time. In-situ relative humidity probes measure moisture inside the slab. Surface meters give a quick screen. A plastic sheet taped to the floor is a rough check, not a measurement.
Testing before coating is standard for professional installs, and it takes little time compared with the cost of a failed floor.
What to do about high readings
Moderate readings can often be handled with a vapor-mitigating primer or a more breathable system. High readings may require fixing drainage, grading or gutters first.
In basements and garages around Nashville with clay soils, it is common to see moisture issues in older slabs, and a test shows exactly where you stand.
Related services
Quick answers
Can I test moisture myself?
A plastic sheet test gives a hint, but professional tests give numbers. It is worth having done properly.
Does a dry-looking slab mean no moisture?
No. Slabs can look and feel dry and still emit enough vapor to damage a coating.
Ready to talk it through? Get a free estimate or call 615-209-7643.