Frequently Asked Questions Regarding Calcium Sulphate-based Levelling Materials
| Are there other test methods for humidity measurement? |
Yes, besides the test methods mentioned above, the humidity could be measured with microwave or infrared radiation. But for on-site testing the CM method supplies the most reliable data. |
| What is the basis for calculating drying times? |
Given standard conditions (20°C/ 50% RH) the drying time of 4cm thick calcium sulphate screed is about 3 weeks |
| Are there differences in humidity content when using drying kiln instead of the CM method? |
When testing calcium sulphate screed there are no great differences between the two methods |
| Who delivers the CM testing equipment? |
Company: Riedel-de-Haen, Germany, Seelze |
| What do you need to look out for when using a base-bonded floor screed? |
The underlying concrete could have a drying time for more than one year. A floor screed can be applied if the concrete on the surface is dry (< 5%). But the screed should not be coated with vapour dense material, for example PVC. Otherwise there damage can occur caused by humidity. |
| water dries out of the screed? |
1% moisture decrease means around 0.8 litre water/m² surface and thickness of 4 cm. |
| What is the maximum heat flow temperature for floor heating systems? |
The maximum heat flow temperature is 55°C |
| At what point can the heating be used? |
Normally after 7 days, with special systems, after 5 hours. |
| Is it sufficient to half-open the windows? |
No. Half-open windows allow only 0.5 air changes per hour, where as fully open windows and doors change the air 40 times per hour. |
| Should the windows stay open during the night? |
Better not, because the inside temperature could fall and there is a risk of condensation |
| Is the drying process in summertime faster than in wintertime? |
Normally not, because in summer the air humidity is usually higher than in winter. However in winter the heating system is in use.
The drying out process depends to a great extent on the air exchange rate. The more air changes per hour, the faster the drying out.
|
Window position |
Air exchange rate per hour |
|
windows closed, doors closed |
0 to 0.5 |
|
windows tipped, roll shutter closed |
0.3 to 1.5 |
|
windows tipped, no roll shutter |
0.8 to 4.0 |
|
windows opened half |
5 to 10 |
|
windows opened fully |
9 to 15 |
|
windows and window-door fully open |
about 40 | |
| Is it possible to speed up the drying time? |
In the case of poor ambient conditions (high humidity, low temperature, no air ventilation) the rate of drying could be increased by using an air dehumidifier, which produces constant dry air. If the ambient temperature is too low, additional heating should be installed. Windows and doors must be shut during drying. The emerging water has to be transported outside the building. |
| Do calcium sulphate screeds need reinforcement? |
Generally not |
| simple test for moisture content in screeds exist? |
Yes, place a plastic sheet on the screed surface and fix it down with impermeable adhesive tape. The next day you will find condensation on the underside if there is still moisture in the screed. |
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