Screeds are usually designed in a single layer, i.e. they are installed in a single operation in full thickness. In certain cases, multi-layer installation may also be useful/necessary, e.g. in the case of utility screeds, if (cost-intensive) aggregates for a coloured or particularly hard surface are added to the upper layer, as in the case of terrazzo floors according to VOB C DIN 18353 section 3.3.
For heavy-duty screeds (industrial coatings) according to DIN 18560-7, a two-layer design is specified in certain cases: e.g. for mastic asphalt screeds with a nominal thickness of over 40 mm or for cement-bound hard screeds/magnesia screeds on an insulating/separating layer.
Source: bauwion
