Testing concrete
Use in-situ relative humidity probes to ASTM F2170 — three probes for the first 1,000 sq. ft. and one per additional 1,000. Readings must sit at or below the adhesive manufacturer's limit, commonly 75% to 85% RH.
Calcium chloride testing (ASTM F1869) measures surface emission only and is a weaker indicator for a slab that will be covered. Where the two disagree, trust the in-situ RH result.
Testing wood subfloors
Take pin or pinless meter readings at a minimum of 20 points per 1,000 sq. ft., averaged. Subfloor moisture content should be at or below 12%, and within 3 percentage points of the flooring for narrow boards.
Flatness and preparation
Flatten to within 3/16" over 10 feet. Grind high spots and fill low spots with a cementitious patch rated for the adhesive system in use.
Remove all adhesive residue, curing compounds, sealers and paint overspray from slabs before gluing. Adhesive bonds to what is on the slab, not the slab itself.
When to add a vapour retarder
Any slab on or below grade, any slab without a documented vapour barrier beneath it, and any installation where testing lands near the adhesive limit should get a moisture-control membrane or a moisture-control adhesive rated for the reading.
Document the readings and the products used. A written record is the difference between a warranty claim being honoured and being denied.
Need this checked against a live job?
Send us the subfloor, the readings and the product you're planning to use. We'll tell you whether it works before the material ships.
Ask the Sunca team