ASTM F2170 — In-Situ RH Testing

It reads conditions within the slab rather than at its surface, which is why it is the reference test before installing flooring over concrete.

Key facts

Why surface tests are not enough

Moisture in a slab is not evenly distributed, and a surface reading reflects the room's air more than the slab's interior.

A slab dries from the top down. The surface can read acceptably while the body of the slab still holds enough moisture to drive vapor upward for months after flooring goes down. In-situ probes read at a specified depth precisely to avoid this.

This is the difference between a test that tells you whether the surface is dry today and a test that tells you what the slab will do to your floor over the next year.

Where this applies in New Jersey homes

It applies to any flooring installed over concrete: finished basements, slab-on-grade additions, and converted garages.

It is most relevant below grade. A finished basement is the single most common place a New Jersey homeowner puts flooring over concrete, and it is also the place most likely to have vapor drive from the ground beneath.

This is also the point where luxury vinyl plank often becomes the correct specification rather than a compromise — not because wood cannot go over concrete, but because the moisture conditions may not support it.

What the test does not cover

The test measures moisture, not the presence of a vapor retarder, not slab flatness, and not bond compatibility with an adhesive.

A passing RH result is a prerequisite, not a green light on its own. Flatness tolerance and adhesive selection are separate questions with separate answers.

Frequently asked questions