How to perform the in-situ concrete moisture content test

What is the in-situ moisture content test

The in-situ moisture content test measures the amount of moisture content present in a concrete slab. The Concrete moisture probe sends a signal from the bottom of the probe, inside the concrete, to the surface.

This can provide an indication of the moisture content within the slab to a depth of up to 4” (100mm). The concrete moisture probe can only be used with a Tramex concrete moisture meter.


The in-situ moisture content test

To use the Concrete Moisture Probe, a hole must be drilled into the concrete.

The location of the drill holes can be determined by the non-destructive impedance tests, where a higher moisture content % reading was recorded.

The hole should have the same dimensions as the hole drilled for the ASTM F2170 in-situ relative humidity test, so the same hole can be used for both tests. It is recommended to perform the CMP test before the hole liner for ASTM F2170 is placed into the hole.

The Concrete Moisture Probe cradle must be used with a Tramex concrete moisture encounter.

CMP test
drill instructions

Step 1: How to drill holes for the in situ concrete moisture content test

The drill recommendations are as follows:

  • The holes must be drilled dry and perpendicular (90 ̊), do not use water for cooling or lubrication as this can affect the test results.
  • The depth of the hole depends on the slab thickness and drying method:
    • When drying is from the top only, it is recommended that the hole should be drilled to approximately 40% of the slab thickness.
    • When drying is from both sides, it is recommended that the slab should be drilled to approximately 20% of the slab thickness

After drilling, the hole should be cleaned of debris and dust. As the probe is not affected by heat from drilling, an in-situ measurement can be taken immediately.

Step 2: Taking a in-situ moisture content reading

To take an in-situ moisture content reading, first adjust the length of the probe to the required reading depth and attach it to the base of the cradle.

Then, insert the probe into the hole so that the cradle sits flat on the concrete surface. 

To take a reading, place a concrete moisture encounter in the cradle and press it firmly onto the slab.

The moisture content percentage can be measured to a depth of up to 4’ (10cm), as the probe reads from the bottom towards the top.

Rotate the cradle in the hole to take a few readings ‘around-the-clock’ and record the highest result.

In situ Concrete Moisture Content reading

Step 3: Reading and understanding the test results

Comparing the in-situ moisture content readings to the surface moisture content reading results can help indicate whether the moisture present in the slab is coming from above or below.

Reading results from the in-situ moisture probe should be ½ - 1 % higher compared to the surface test results.  

A higher reading indicates elevated moisture from below, while a lower reading indicates elevated moisture from above.

If you need to drill several holes in your test area for performing the ASTM F2170 test, it is recommended to check each location with the concrete moisture probe before fitting the hole liners.

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