While concrete is drying, the surface will generally have a lower moisture content than deeper down in the slab.

So you won't really know how much moisture is present if you only do a surface test.

It's also the case that slabs often have integrated beams and other areas of thickening where extra strength is required. This means that these parts will dry more slowly than the rest of the slab.

So you should do at least one test for each level of concrete (or each separate concrete pour) where the thicker areas are.

You also need to test the slab in a range of places to make sure there are no other areas with unusually high concentrations of moisture.

The same principle applies to timber subfloors.

Different timber components may have had different moisture contents when they were installed, depending on whether they were supplied kiln dried or green from the sawmill.

There could also be particular areas in the building with moisture problems - such as through leaking water pipes, poorly sealed flashing or subfloor ventilation problems.

Again, you'll need to test the subfloor timbers in various places to make sure you've got an accurate picture of the moisture levels.

RH and MC levels

The Australian Standards for textile floor coverings (AS 2455) and resilient coverings (AS 1884) specify different relative humidity (RH) or moisture content (MC) levels, depending on which moisture testing method is used. These are shown in the table below.

We'll talk about how to physically carry out these tests in the following lessons.

Note that the figures shown below are general specifications in the Standards. Manufacturers of adhesives, coatings, levelling compounds and floor coverings may have different specifications listed in their installation guidelines.

There may also be particular regions in Australia where these general limitations are not appropriate, such as in North Queensland where the atmospheric RH can stay very high for long periods of time.

Subfloor	Testing method	Moisture level
Concrete	RH surface-mounted insulated hood test	Maximum RH: 70%
Concrete	RH 'in-situ probe test' in concrete	Maximum RH: 75%
Timber	MC test in timber.	MC range: 10-14%. (Note that for timber floor coverings, the MC range is 9-14% for all species, except cypress, which is 10-15%.)

For concrete subfloors, three tests need to be carried out in the first 100 m² of floor, plus one extra test for every additional 100 m².

Tests may also need to done in other positions, depending on the structure of the floor.

Testing methods

For testing RH in concrete, AS1884-2012 (the new resilient flooring Standard) follows the 'in-situ probe' testing methods set by the American Society for Testing and Materials (ASTM).

On the other hand, AS/NZS 2455.1:2007 (the older but still current Standard for carpet) uses a modified version of the ASTM 'insulated hood' test.

We'll describe both of these methods in the following lessons, but if you want to see the full details you should look up the original ASTM documents listed below.

But remember, in addition to following the methods described in the ASTM documents, you still need to comply with the instrument manufacturer's instructions.

Occasionally, you might find that the ASTM and instrument manufacturer say two different things. In these cases, you should ask the floor covering manufacturer how to proceed.

For timber subfloors, the testing methods are defined by the Australian Standards.

Again, we'll describe the general methods later in this section, but you should also look at the original documents listed below.

Test report

It's in your interests to fully document the testing you carry out, and record the following details:

• jobsite address
  
  
• type of subfloor tested, slab thickness and depth of the holes that you've drilled
  
  
• date and time of testings
  
  
• where the tests were carried out (with the positions marked on the floor plan)
  
  
• what the moisture and pH readings were (preferably with photographic evidence)
  
  
• subfloor temperature, ambient temperature and RH at the time of testing
  
  
• test equipment type, make, model, serial number and calibration status.