Pumpable self-smoothing screeds
These are covered by BS 8204, Screeds, bases and in-situ floorings, Part 7: Pumpable self-smoothing screeds – code of Practice (2004).
These are often referred to as ‘self levelling screeds’ and can be used as a levelling screed or a wearing screed. They are defined as ‘screed that is mixed to a fluid consistency, that can be transported by pump to the area where it is to be laid and which will flow sufficiently to give the required accuracy of level and surface regularity’.
Pumpable self-smoothing screeds are proprietary materials and comprise of two main types: cementitious and calcium sulfate. Cement based pumpable self-smoothing screeds tend to be used when a thin screed section is required, when the screed is to be a wearing screed, receive a synthetic resin flooring for an industrial floor or when rapid drying is required. Calcium sulfate based pumpable self-smoothing screeds tend to be used when the screed section is to be thicker or where there is a requirement for an unbonded or floating screed.
Where an existing screeded floor is to be replaced, calcium sulfate based pumpable self-smoothing screeds allow thermal insulation to be laid. The thinner screed and a layer of thermal insulation can be laid within the same thickness as the original thicker conventional cementitious screed.
Further reading: PYE, PW and HARRISON, HW. Floors and Flooring, BRE, 2003.