We dealt with two issues this week relating to problems caused by construction moisture. A plaster beetle infestation and an investigation into the reasons why anhydrite floor screeds were not drying out within a multi-million pound residential development block in London. More on the plaster beetle infestation in a separate blog to follow quite soon.
Our client, was understandably concerned that pumped anhydrite floor screeds, which on some floors had been pumped in 6 weeks earlier, had failed to dry. The installation process for this particular screed required that the laitance be sanded from the surface of the floor once dry, this usually occurs at 3-7 days after installation, however any attempt at sanding the floor immediately resulted in a clogged rotary sanding pad.
Laitance occurs on the surface during settlement/compaction. During this compaction process, bleed water migrates to the screed surface. This brings with it fine particulates within the screed. Laitance is subsequently formed as a result of the evaporation of the bleed water, and once hardened can impede the drying process .
The advantages of laying a pumped anhydrite screed, as opposed to laying concrete is that you can generate quite significant savings on labour and time but only if optimum environmental conditions for drying the screed are present.
Other benefits of using pumped calcium sulfate screeds are that they are self compacting, have very little shrinkage and rarely require movement joints. They are particularly suited to underfloor heating systems because they dissipate heat far better than a concrete floor slab would. Click on link above for full article.