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Concrete Moisture Testing

  • Posted by: Alex Wilkie

What is a concrete moisture test?

A concrete moisture test is used to determine how much moisture is present – usually in order to know if flooring can be safely installed without causing issues. Measuring the moisture of a concrete slab can be done in several ways, but currently the only methods approved by Australian standards measure the relative humidity of the slab. The most common method, uses in-situ probes (ASTM F2170). In this method holes (at least 1 / 100m2) are drilled to a specific depth in the slab, a sleeve is installed into the holes to create a small chamber with an open base inside the slab.  This allows the air inside the chamber to equalise to the relative humidity of the slab. The sleeve is left for a minimum of 1 day for the chamber to equalise with the concrete slab. Following the equalising period, the relative humidity is read using a thermohygrometer or relative humidity sensor.

When should you do a concrete moisture test?

If you intend to install resilient flooring – vinyl, tiles, etc., testing the concrete slab for moisture is a requirement of the Australian standards (AS 1884-2012). It is also best practice as it will help prevent issues and ensure longevity of the floor covering. Concrete moisture testing may also be required if there are unresolved moisture issues or problems with flooring occurring and problems like leaks and rising damp need to be ruled out. Additionally, once a moisture problem is identified, monitoring of the moisture in the concrete slab will provide data on when remediation works have been completed, and when the next stage of repairs can continue.

What do the results mean?

Once you complete a measurement of the moisture in a concrete slab done according to the Australian standards you will receive relative humidity value(s) as a percentage. The standards make it very simple: the relative humidity of a concrete slab should be less than 75% before installation of resilient flooring. Installation of resilient flooring on concrete with relative humidity above 75% has increased risk of causing damage to the flooring, causing failure of adhesives and releasing moisture into the internal environment – which may lead to other moisture related issues such as mould growth.

What to do if moisture in the concrete slab is high?

Try to determine what is the source of the moisture in the slab. Drying of the slab will not be effective unless the issue is resolved. Once the moisture source has been fixed, allow time for the slab to return to normal moisture levels. This may take many months, or equipment can be used to speed the process. The four main factors which affect the rate a concrete slab dries are time, temperature of the slab, relative humidity of the ambient air, and airflow across the slab. For more information on how to dry a concrete slab see this article.

Are there any other ways to test concrete moisture?

Other methods of measuring the moisture in a concrete slab include creating a chamber above the slab surface, sealed to the slab and measured in much the same way as in-situ testing. This method is also in the Australian standards, however is rarely used over the in-situ probe testing.  In the past, electrical conductivity on the slab surface was used, but this method has lost favor as it only measures moisture near the surface of the slab. Moisture meters based on short range microwave signals can also be used to measure moisture within a slab, but have not yet been added to approved methods in the Australian standards of measuring concrete moisture. Regardless, surface conductivity and microwave measurement do have their applications, notably that they can obtain fast results.

What else can affect installation of flooring on concrete?

If you are experiencing difficulties with resilient flooring on concrete slabs consult a professional. The most common issue – after moisture – is the pH of the concrete slab. The Australian standards recommend that pH of the slab be between 7.0 and 10.0 and should not exceed the manufacturers specifications of working ranges for the adhesive (ASTM F710-17).

How do I book a concrete moisture test?

Simply send us your inquiry by phone or email and we will arrange for an experienced technician to attend the site and conduct testing.

 

References

  1. AS 1884-2012, “Floor Coverings – Resilient sheet and tiles – Installation Practices”
  2. ASTM F2170-18, “Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using In Situ Probes”
  3. ASTM F710-17, “Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring”