Of all the problems that can occur in a finished floor, the ones that stem from high moisture or pH levels are likely to give you the most trouble.

That's why you need to be very thorough in your moisture and pH testing before you start any preparation work.

Moisture levels

Set out below are the relative humidity (RH) and moisture content (MC) levels permitted under the Australian Standards for textile floor coverings (AS 2455) and resilient coverings (AS 1884).

Note that these figures are general specifications - manufacturers of flooring products may have different specifications listed in their installation guidelines.

There may also be particular regions in Australia where these limits are not appropriate, such as in North Queensland where atmospheric humidity often remains high for long periods of time.

For each subfloor, three tests need to be carried out in the first 100 m² plus one extra test for every additional 100 m².

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

Concrete subfloors

For the surface-mounted insulated hood test, the maximum relative humidity allowed is 70%

For the in-situ probe test, the maximum RH is 75%

If it turns out that the RH level is not acceptable for the coatings or toppings you're planning to use, you will have to make a choice - either:

• wait until the concrete dries down to an acceptable level, or
  
  
• apply a moisture barrier to the surface.

Timber subfloors

In timber subfloors, the allowable moisture content (MC) range is 10-14%

If the moisture content is above 14%, it could mean there's a subfloor ventilation problem or that the floor has been flooded due to a broken water pipe or some other plumbing problem.

In these cases, you'll need to address those issues first and then wait for the floor to dry.

pH levels

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

The pH level should be within the 9-10 range.

Again, three tests need to be carried out in the first 100 m², plus one extra test for every additional 100 m².

Note that freshly poured concrete always has high alkalinity (often with a pH of 12-13), because this is a by-product of the chemical reaction occurring between cement and water.

So you don't need to be concerned about high pH levels while the concrete is still drying.

However, if the concrete has reached equilibrium moisture content (EMC) and the pH is still too high, you'll need to take some action.

The most common treatment is an acid wash. We'll talk more about this in the next lesson.