Concrete Moisture Testing

15 

Q&As

Please note for floor coverings, moisture is measured in Relative Humidity (RH), so throughout this Q&A, we will note moisture as RH.

1. Why should I moisture test my concrete subfloor?

It’s a requirement of the Australian Standards AS 2455.1:2019, AS 2455.2:2019 and AS 1884:2021 and the floor covering manufacturer’s instructions.

2. What is the difference between concrete slab curing and drying?

Curing takes approximately 30 days for a concrete slab to achieve the desired properties for its intended use.

Drying is the time it takes to meet the floor covering manufacturer’s recommended RH & pH levels to install the floor coverings. The time varies greatly depending on the slab thickness

  • drying from 1 side or 2
  • the water/cement ratio
  • ambient conditions
  • the surface finish (i.e. overpower trowelled surfaces retard the drying time)

Testing has shown that the drying time of a 150mm slab can be double that of a 100mm slab, and a 200mm slab can be triple that of a 100mm slab.

3. When does a slab start to dry?

A slab starts to dry from the time it gets poured; however, a concrete slab is like a sponge, and it will rehydrate from water ingress. A slab is considered to be drying in preparation for the installation of floor coverings from the last time it got wet.

4. When should I moisture test the subfloor?

Moisture testing of the subfloor should be undertaken a few days before the floor coverings are installed to replicate the RH conditions of the slab that the floor coverings are being installed on.

5. How many moisture tests do I need to undertake?

The resilient floor covering Standard AS 1884:2021 require that you undertake three (3) tests for the first 100m2 and then one (1) for every 100m2 thereafter.

The textile floor covering Standards AS 2455.1:2019 and AS 2455.2:2019 state that for indicative testing, you undertake not less than one (1) test per 500m2, and if a more definitive survey of the floor area is required, the number of tests should increase by one (1) additional test per 100m2.

If, however, you are testing in accordance with ASTM F2170 ‑ 19, then three (3) tests for the first 100m2 and then one (1) for every 100m2 thereafter.

6. How far do I drill into the slab to do an in-situ probe test?

For a slab on the ground or on metal decking (which is drying from the top only), you drill to 40% of the thickness of the slab. For a suspended slab (which is drying from both sides) you drill to a depth of 20% of the thickness of the slab.

7. Do I need to test an old slab before laying a new floor covering?

Yes, environmental and building conditions change over time, and it’s a requirement of Australian Standards AS 2455.1:2019, AS 2455.2:2019 and AS 1884:2021 and the floor covering manufacturer.

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8. If the floor covering manufacturer’s installation instructions are different from the Australian Standard, which do I follow?

Always follow the manufacturer’s instructions over Australian Standards. The manufactures’ instructions are specific for their product, whereas the Australian Standards are a minimum best practice guide.

9. My adhesive, levelling compound and flooring product all state a different RH requirement. Which RH requirement do I follow?

Follow the manufacturer who states the lowest RH requirement.

10. Can I use a surface meter to test the moisture in a slab?

No, a surface test will only give you a qualitative test result, and a flooring manufacturer will only warrant their product when quantitative testing has been undertaken, such as the in-situ test in accordance with ASTM F 2170 ‑ 19.

11. Do I need to undertake pH (alkalinity) testing of the subfloor?

Yes, the Australian Standards AS 2455.1:2019, AS 2455.2:2019 and AS 1884:2021  and most floor covering and adhesive manufacturer manufacturers require that you undertake pH testing of the subfloor.

12. How many pH tests do I need to do?

The resilient floor covering Standard AS 1884:2021 require that you undertake three (3) tests for the first 100m2 and then one (1) for every 100m2 thereafter.

The textile floor covering Standards AS 2455.1:2019 and AS 2455.2:2019 state that for indicative testing, you undertake not less than one (1) pH test per 500m2, and if a more definitive survey of the floor area is required, the number of pH tests should increase by one (1) additional test per 100m2.

13. Do all floor covering manufacturers require the subfloor to be moisture tested?

Yes, all floor covering manufacturers require the subfloor to be moisture tested even those that state  their products can be installed over a slab with 99-100% RH.

14. What if the test results are only slightly higher than the floor covering manufacturer’s recommendations, or some results are higher, and others lower than the floor covering manufacturer’s recommendations?

Please speak to the floor covering manufacturer, and unless they are prepared to give you a warranty based on your results, a moisture abatement system will be required.

15. How does the water/cement ratio affect the RH of the slab?

Generally, the higher the water content in the water/cement mix, the longer the slab will take to dry and the longer it takes to dry, the longer the slab will have an elevated RH and/or pH.

Should you have any queries, please contact ATTAR on 1300 139 155 or info@attar.com.au.