get down to a very low percentage moisture content by weight (around 0.7 to 0.8%) before the relative humidity starts to drop very quickly according to the characteristics displayed by the materials’ adsorption curves.
This means that someone measuring the humidity on an anhydrite screed
for a long period of time will feel very insecure and not really know if they are getting anywhere with the drying process. They might continually measure 95 to 100% ERH without seeing any drop, yet the screed may be drying very well. It is only when you use other measurements (measurements of moisture by weight) that you know that things are progressing in the right direction and can predict that the desired fall in the relative humidity will happen soon.
Such knowledge allows the constructor to be optimistic that deadlines will be met. It also means that when things are not progressing well, action can be taken to install drying processes, or to consider the application of a surface damp proof sealant. Measuring moisture content by weight can be carried out using a Speedy Meter (AKA Carbide test) or by using some specialist radio wave transmission meters for example Tramex CME.
It is clear that being conscious of elevated moisture levels, how to measure them and taking action at an early stage, saves significant time and money. If it comes close to your handover date and you are considering a forced drying regime – then you have probably set yourself quite a challenge. If you have left monitoring late and suddenly decide there is a need to reduce moisture levels, you might have to resort to an emergency strategy. This might involve partially drying the floor and then using a surface vapour barrier (a fairly expensive solution) which then locks the moisture into the building. This also can reduce the building’s insulation value and the moisture could then, depending on construction method, find its way into the walls.
In conclusion, we recommend that the moisture content of screeds is evaluated early, that laitance is removed from anhydrite screeds and measures taken to make sure that the screed is protected from any further wetting from rain or site activities. Failure to do this can lead to contractors missing deadlines and incurring post-handover claims for deterioration after occupation because of higher moisture levels.
Richfords Fire & Flood is offering CPD training on these issues from 2017.
www.richfords.com
twitter.com/TContractFloors FEATURE | 41
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