Is your slab ready for flooring?

WHY should concrete slab moisture be an increasing problem for flooring installations over the last 5 or so years? Why is Relative Humidity (RH) Moisture Testing for Concrete Subfloors now in demand more than before?

Are concrete contractors using more water? Can we blame them for the spate of failures of late?

Well, no, of course not. They have to use more water in some cases- where excessively dry conditions can cause the concrete to crack, for example. Using more water helps the curing, and therefore the strengthening process of concrete. In fact, for major structural projects, engineers are using a combination of drying rate measurements and heat measurements in concrete structures to determine its overall strength. It’s called the maturity method. But that’s another story, for now (fascinating though it is).

Indeed, the water in concrete’s original pour is a part of life for flooring installations and we have known this for some time.

Certainly the “greening” of adhesive and other products has made them more susceptible to moisture and alkaline attack. There is little doubt in the industry that this is a prevalent issue.

Green building codes and lower-VOC products are also a part of life, and adaption to them is required. But this alone is not the problem either.

Flooring industry boffins (that’s not a rude word by the way) has always agreed that moisture is an issue which needs to be tackled, but have not really agreed on how to measure it.

With almost 12 years in the timber flooring industry, I know that the timber folks were well accustomed to, and dependent upon, the “Moisture Meter” (electrical resistance) way of measuring. It was great- because the parameter was simple (nothing over 5.5% moisture content, down goes the floor). Even better than that, the meters were easy to use. Turn ’em on, hold ’em down, and look at the little needle.

What changed? Well, two things: It was always known to be the case that these measurements only scratched the surface of the concrete- literally- just a few mm’s. Also, it only measure the water which was THERE, rather than the water which HAD NOT FORMED YET. But only recently was it decided that this was a problem. Or, perhaps, it was that a better way was found.

Meanwhile, increased use of additives in concrete mix (green influence again) such as fly ash (waste material) was found to be skewing the resistance meter’s readings.

Only by measuring humidity deep within the slab, would a reading be found which would best paint the picture of what a flooring installation was most likely to experience if laid down at that time.

If only things could stay simple. But the Devil is always in the details, and Relative Humidity (RH) Moisture Testing for concrete subfloors has emerged as the method most widely acknowledged for its accuracy and relevance.


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