Screed

Screed has three meanings in building construction. 1) a flat board (screed board, floating screed) or a purpose-made aluminium tool used to smooth and true materials like concrete, stucco and plaster after it has been placed on a surface or to assist in flattening; 2) a strip of plaster or wood applied to a surface to act as a guide for a screed tool (screed rail, screed strip, screed batten); 3) the material itself which has been flattened with a screed (screed coat). In the UK, screed has also come to describe a thin, top layer of material (traditionally sand and cement), poured in site on top of the structural concrete or insulation, on top of which other finishing materials can be applied, or it can be left bare to achieve a raw effect. It is becoming more common to use "self-leveling" poured screeds which use materials other than cement as their binder.

In the US, screeding is the process a person called a concrete finisher performs by cutting off excess wet concrete to bring the top surface of a slab to the proper grade and smoothness. A power concrete screed has a gasoline motor attached which helps smooth and vibrate concrete as it is flattened. After the concrete is flattened it is smoothed with a concrete float or power trowel. A concrete floor is sometimes called a solid ground floor.

A plasterer also may use a screed to level a wall or ceiling surface in plasterwork.

This sense of screed has been extended to asphalt paving where a free floating screed is part of a machine which spreads the pavement.

A weep screed or sill screed is a screed rail which has drainage holes to allow moisture which penetrated an exterior plaster or stucco coating to drain through the screed.

Flowing screeds are made from inert fillers such as sand, with a binder system based on calcium sulphate. Consequently they can look very similar to a sand/cement screed Flow screeds are often preferred to traditional cement based screeds as they are faster to install and provide a similar finish. Flow screed is most often used in combination with underfloor heating installation as the reduced thickness provides for more effective and efficient heat transfer.

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