Anhydrite screeds contain no coarse aggregate so this in itself is clearly a paradoxical practice doomed to failure. In actual fact over-sanding can be counter-productive and is more often than not completely unnecessary. Laitance is often stated as the reason for this level of effort.


Laitance is often misunderstood and occurs with all screed types regardless of binder mechanisms used. It is simply the layer of particulate matter which migrates to the surface of the screed with bleed water during initial setting. There is the mistaken perception that if it is not removed early from the screed, it impedes drying. Independent testing that has been carried out concludes that this is not the case. There is a perception that if it is left in place for too long then it becomes hard to remove. The fact is that if it cannot be removed without a great deal of effort it does not need to


be removed at all. Another misguided notion is that all anhydrite screeds produce laitance and so must be sanded more than other screed types. In fact, there are a number of anhydrite screeds that use specialised technology at mixing stage, which prevent the formation of loose friable laitance. People often forget or ignore the real reasons for sanding the floor screed – which is the removal of site debris, to provide a key and to remove any loose and friable particulates from its surface.


The surface of the screed needs to be hard and free from loose extraneous construction debris. So, in essence anhydrite screeds require no more sanding than any other screed types. Therefore, the need for sanding is not an appropriate criterion on which to base a screed selection.


www.lkabminerals.com/en/products/gypsol


www.lkabminerals.com/en/ products/gypsol


twitter.com/TContractFloors


SUBFLOOR PREPARATION | 33


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52