Undercoats and primers form the bonding bridge between the substrate and the levelling compound or the adhesive applied on top. Their use is prescribed by DIN 18365 "Flooring Works". It is always necessary to follow the manufacturer's instructions for use.
Screeds form the load distribution layer. They are normally installed on top of concrete floors. When produced as in-situ screeds, they are made from aggregates (gravel, sand etc.) and suitable binders. A fine aggregate is used for screed production in order to ensure layers with a smoother and more even surface.