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Unit: Inspecting and testing subfloors

LMFFL2004A: Moisture test timber and concrete floors
LMFFL3101A: Inspect sub-floors

Section 4: Measuring moisture and pH

Measuring pH levels

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When the alkalinity in a concrete subfloor is too high, it can stop the floor covering adhesive from bonding properly to the concrete.

Although this problem has always existed, it hadn't been fully realised by flooring installers until quite recently.

This is partly due to the fact that the materials used by installers have changed over time.

It's also due to continuing research and a much better understanding of the importance of pH levels.

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The new Australian Standard for resilient flooring installation (AS 1884-2012) now says that a pH test must be carried out on a concrete subfloor as part of the pre-installation assessment.

The minimum number of tests required is the same as for moisture testing - three in the first 100 m2 of floor, plus one extra test for every additional 100 m2.

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What pH means

pH is a measure of how acidic or alkaline a material is.

In scientific terms, 'p' stands for 'potential' and 'H' is the chemical symbol for hydrogen - so 'pH' means 'potential hydrogen', or the ability to attract hydrogen ions.

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Materials with a low pH level are more acidic and have a lower attraction for hydrogen.

Materials with a higher pH are more alkaline and have a higher attraction for hydrogen.

The balancing point is 7. If the pH is lower than 7, it is more acidic; if it's higher, it's more alkaline.

When it's right on 7, it's called 'pH neutral'.

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Freshly mixed concrete is extremely alkaline - well above 10 - but the pH level drops as the concrete cures.

AS 1884 says that the pH level of the concrete surface should be between 9 and 10 before the flooring installation is commenced.

However, it also says that the final level should be determined by the adhesive manufacturer.

You should also check on the pH requirements of other manufacturers' products that you might be using on the subfloor, such as moisture barriers, epoxy coatings and leveling compounds.

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Measuring pH

One way to measure pH is to use paper test strips, which change colour according to the alkalinity of the concrete.

A more accurate way is to use a pH meter, which gives a numerical reading via a digital display.

The testing procedure is as follows.

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Step 1 Sand a small section of the concrete surface with 200 grit sandpaper.

This will remove any impurities from the surface that might affect the test results.

Remove the dust with a vacuum cleaner.

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Note that if the surface is still not porous after sanding - that is, if it doesn't pass the water drop test - you'll need to use a hand grinder to remove the non-porous material.

Remember, if the water is beading on the surface, you won't get an accurate pH reading because you'll only be testing the pH of the water drop itself.

If you do have to mechanically prepare the surface, it's best to wait until just before you install the floor covering so that your pH test is done on the actual floor surface you'll be installing over.

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Step 2 Put several drops of distilled or 'de-ionised' water onto the prepared surface.

The water must have a pH reading of 7 - you can use the test strip or meter to check the water's pH before you use it.

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Step 3 Leave the drops for 60 seconds and then place the test strip or meter reader in the water.

Wait for the period of time specified by the manufacturer.

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Step 4 If you are using test strips, compare the colour of the strip to the pH colour chart.

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If you are using a pH meter, read off the digital display on the meter.

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Learning activity

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Flooring Resources have produced a video clip called 'pH test for concrete' which describes how their pH test kit works. The link below will take you to the clip.

pH test for concrete

pH testing is still quite new for concrete floors, but there are other pH tests that people do all the time, including in their own homes. One example is testing pH levels in swimming pools.

Another is testing the soil in vegetable gardens, especially when certain types of vegetables aren't growing as well as they should.

Have you used a pH test kit before? What were you testing? How did the system work?

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