What You Need to Know About the Hygrometer Screed Moisture Test

I’m Andy Parkin Managing Director at the Multi Award Winning Speed Screed. Today I would like to talk about the hygrometer screed moisture test and how it is performed.

Why The Hygrometer Screed Moisture Test?

The single largest failure of floor coverings is too much moisture, laying the coverings before the screed or concrete is dry enough.  Yes, it may look dry, but no matter how many years of experience you may have the only way to know 100% if the screed is dry enough to bond is to conduct a moisture test.

The British Standard clearly indicates the need for a moisture test. BS 5325, BS 8201, BS 8203 for textile, wood, and resilient floor coverings, respectively.   The recommended method would be to carry out a hygrometer screed moisture test.

A hygrometer is used to measure the Relative Humidity (R.H) of the air contacting the screed. It is done over a small volume and the air is isolated from surrounding air. A series of tests are performed to ensure that the R.H is not more than 75% for most floor coverings. A maximum of 65% R.H is permitted for solid timber floor coverings.

To perform the hygrometer screed moisture test, a digital hygrometer is required. Also, you will need an insulating box with butyl sealing tape and a data sheet to crosscheck the values. Digital hygrometers can measure the Relative Humidity as well as the air temperature.

Hygrometer Screed Moisture Test

The test begins with ensuring that any external methods of drying the screed are turned off at least 4 days before the test is performed. The floor should be clean and free of any dust particles. Getting some insight about the property certainly helps to determine the area where you should be performing the test, with least ventilated areas being the obvious choice to start with.

Now, position the digital hygrometer along with the insulating box on the floor and seal the edges with butyl tape. If butyl tape is unavailable at the time of the test, any kind of waterproof putty can be used.

It is crucial to ensure that the instrument is turned off because the air inside needs to reach the moisture equilibrium. Once the instrument is positioned, completely seal it off and leave it. If the surface is uneven, make sure to use at least two layers of tape so no air can escape. Leaving the instrument overnight is a good practice.

Once it is time, the actual hygrometer screed moisture test can begin by turning the instrument on.

The ideal time to wait before the first reading is taken is 4 hours for 50mm thick screeds. The thicker the screed, the more time should be allowed to pass.

A trick to reduce the time of the instrument sitting idle is to seal the floor with polythene sheets or rubber mats at least 3 days prior to the test. Once the mat is removed, place the instrument in the centre immediately and seal it off. Moisture equilibrium will be achieved within 4 hours in this case, but leaving it overnight is best practice.

Takeaway

Hygrometer screed moisture test is an essential step before installing floor coverings. It will determine whether the floor is ready or not to receive floor coverings. Depending on the results, further actions may be required.

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