Anhydrite (Calcium Sulphate) Floor Preparation
Anhydrite screeds have been commonly used in construction projects over the last 20 years as an alternative to traditional concrete screeds, mainly due to the fact that they are much less labour intensive to lay and are very compatible with underfloor heating systems. They also have a much faster drying time, being ready for light foot traffic after 48 hours and being worked on after 4-5 days.
During the drying process, laitance forms on the surface of the screed. This must be ground off before any accurate hygrometer reading can be taken. If a cement based smoothing compound is laid over a moist anhydrite screed, Ettringite may be formed, which is an expansive crystal that can lead to failure of the floor (blown screed). For this reason it important that the laitance is removed. This is the job of the contractor who laid the screed, however we understand that this may not always be possible, or you may not know who the person who laid the screed was if you have moved into a new home.
We offer a service where we remove the laitance using a floor grinder either alongside other works we are undertaking for you, or as a standalone job to allow another tradesman to come in after. Floor grinding does not require any materials, so can generally be done on short notice.