Is the Job Site Right for RH Testing?

RH Testing of Concrete & Screed Needs “In-Service Conditions” to Work Properly

Relative Humidity testing of concrete and cementitious screeds (whether it be done with the ASTM F2170 probe method or the BS Standard Humidity Box) is an accepted method of testing for suitability to install a floor covering or coating. However it is important to note that these tests should only be performed in an "air-conditioned" environment, where temperature and humidity are regulated and stable. In other words, in “In-Service Conditions".

The more precise term for this type of testing is ERH with the E standing for "Equilibrium" Relative Humidity.?This involves trapping a portion of air and allowing it to come to equilibrium with the material (in this case concrete or screed) by means of a British Standard Humidity Box or an ASTM approved RH Hole Liner. Equilibrium means that no more Moisture Vapor is passing from the material into the trapped airspace, or vice versa. The airspace is in balance with the material.

However,?this fine balance of equilibrium?requires that?the temperature?remains?stable for long enough to?both?achieve equilibrium,?and?long enough for the tester to?get to site and take the measurement. Any small change in temperature?during the process?will throw this balance out by a potentially large number?of?ERH percentage points.

The chart below illustrates a small change of 1oC (approx. 3oF) can have a large effect on the ERH.

To highlight the need for stability, both British Standards and ASTM discuss the temperature stability in their respective published standards:

British Standard 8201, 8204 & 5345 state that the box test should “… create an enclosed pocket of air which is isolated from the humidity and fluctuations in temperature of the outside air.”

ASTM F2170 is more explicit with: “Concrete ?oor slabs shall be at service temperature and the occupied air space above the ?oor slab shall be at service temperature and service relative humidity for at least 48 h before making relative humidity measurements in the concrete slab.”

All too often we speak to customers who are having difficulty using these test methods on building sites which are open to the elements and which, a lot of times, don't even have doors or windows installed.

The reality is that RH Testing is not suitable in these conditions!

The following article has much more detail, but please message me for more information: