How to Test a Concrete Floor for Moisture Before Epoxy
Moisture coming up through a slab makes a floor coating lift. Test the concrete before you order. The test takes five minutes to set up and 24 hours to read.
The plastic sheet concrete moisture test
- Cut a 2 ft square of plastic sheet.
- Tape it to the bare concrete and seal all four edges.
- Wait 24 hours.
- Peel it back. Water under the plastic or a dark spot on the concrete means the slab is damp.
On a large floor, test more than one spot.
If the test shows a damp slab
Roll on P-409 Moisture Vapor Primer before the base coat. One 1.5 gal kit covers about 140 sq ft. Call (877) 703-7699 and we will size it for your floor.
If the slab is dry
No primer is needed on ground or etched concrete that passed the test.
Basement slabs fail more often
Slabs below ground are damp more often than garage slabs. In a basement, skipping the primer on a damp slab is the most common reason the floor peels.
A primer handles moisture vapor. It does not stop water that comes in through the walls or the slab after rain. Fix leaks before you coat.
