Screed

According to DIN EN 13318, the European standard issued by the German Institute for Standardisation, screed is defined as one or more layers of screed mortar laid on site directly onto the substrate, with or without bonding, or onto an intermediate separating or insulating layer, to fulfil one or more of the following functions:

• to achieve a specified height level
• to receive a floor covering
• to be used directly

Traditional cement screed mortar generally consists of cement, aggregate with a grain size of 0–8 mm, and water. The properties of screed, such as drying time, strength development and workability, can be influenced by using screed admixtures or by replacing the entire cement component with special binders (rapid cements).

In the context of reducing construction times, the drying behaviour of screed is very important. Using admixtures or rapid cements accelerates the drying process, enabling earlier readiness for floor coverings. Screed is ready for covering when it can support the durable, damage-free installation of a floor covering. The key criteria for assessing readiness are:

• residual moisture content
• sufficient strength
• adequate shrinkage and stress reduction

As it is not possible to assess strength and shrinkage behaviour on site using conventional craft methods, these parameters should ideally be determined prior to installation during a suitability test. The only feasible on-site measurement is the CM measurement, which determines residual moisture and indicates readiness for covering.