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Reliable Moisture Assessment Test in Screeds

The retention of excessive moisture in screeds is a major problem that affects the quality and longevity of floors. As it is often difficult to predict the drying times accurately, it is always important to carry out a reliable moisture assessment test prior to the installation of the final finish.

According to industry benchmarks, a standard traditional screed of 75mm thickness usually takes 110 days for optimal drying- provided good airflow and a controlled temperature of 20°C and Relative Humidity of 50% are maintained. This is however different for modified screeds, and may vary from one brand of screed to another.

As per the British Standards Code of Practice, the traditional hair hygrometer test is recommended for estimating the relative humidity in screeds. However, this is a time consuming process and is not a recommended test method for certain modified screeds that form a chemical bond with water.

As modified screeds are currently not covered in the British Standards Code of Practice, manufacturers generally prefer the Moisture Content Test for screeds, as these yield speedy and more accurate results.

The commonly used Moisture Content Test in screeds are:

Calcium Carbide Test:

The moisture content of the screed is assessed by testing a sample of the screed using a carbide moisture meter. A sample of the screed is removed at approximately 50% of the screed depth, and the weight of the sample is measured accurately.  The removed screed sample is further mixed with a calcium carbide reagent and subjected to orbital rotation in a vacuum flask. The results are displayed on a pressure gauge as CM%. The test is relatively quick and easy to carry out, and yields accurate results. However, as the calcium carbide method is a destructive form of testing, minor remedial repairs would generally be necessary for the screed area from where the sample is removed.

Tramex Meter:

This is a non-destructive method for the assessment of moisture content in screeds, and the results are read directly from the screed surface using an electronic meter. The meter assesses the moisture content of the screed by measuring the electrical impedance of the screed. Low frequency signals are emitted by electrodes with spring mounted probes, placed on the screed surface, and the results are instantly displayed on the Tramex meter. Readings taken from a Tramex are for guidance, whereby higher than expected results should be further checked with the Calcium Carbide Test.