For home usage, a screed’s mechanical strength must be at least 20 MPa, but for industrial use, it must be at least 30 MPa in order to lay any kind of flooring.
The screed ought to be uniformly thick throughout and compact on the surface.
It is vitally crucial that the screed is cured and that the majority of the shrinkage is finished prior to laying any kind of flooring.
In favourable conditions, a typical sand-cement screed takes 7 to 10 days to cure for every millimetre of thickness. Therefore, the turnaround time for a screed built from conventional cementitious mortar might be very extensive (more than one month).
Screed fractures can be caused by a variety of factors, including hygrometric shrinkage, too much water in the mix, and the use of too-fine particles.
The screed’s surface needs to be spotless.
To avoid compromising the adhesion between the flooring and the screed, dust, filth, disconnected regions, debris, and any other material or substance on the surface of the screed must be removed before installing the flooring.
It is necessary to measure the screed’s residual humidity. Particularly when installing flooring that is sensitive to humidity, it must correspond to the maximum level for that type of floor covering and must be uniform throughout the whole thickness of the screed.
Levels of less than 2% for wooden floors and less than 2.5–3% for PVC, rubber, and linoleum are acceptable for cementitious-based screeds. No matter the kind of floor covering used, residual humidity for anhydrite screeds must be less than 0.5%. Moisture content should be less than 6% for tile and stone installation.
A straightedge at least 2 metres long should be placed on the screed surface in all directions to determine whether it is flat. Although the allowable tolerance varies depending on the length of the straightedge being used to check for flatness, the highest acceptable tolerance for this specific straightedge is 2 mm.