The screed

What is the screed and how to make it

The screed is a horizontal layer belonging to the package of the slab which has the function of adjusting the laying surface for the subsequent entrapment of the flooring and at the same time, to separate the structural elements from the surface finish.

Its thickness part on average by 4 cm and can be up to 8 cm when used for the definition of the slopes in balconies or flat roofs of buildings.

Inside can be embedded the pipes of the heating systems, water and discharge of bathrooms and kitchens.

On some occasions the screed can work with the reinforced concrete structure of the floor; in that case there can be inserted a welded mesh, knitted usually 20 x 20 cm and a thickness content between 6 and 8 mm.

Mixture for screed

A traditional mixture for the screed consists of a mixture of cement, sand of varying grain size and water. The doses of the various ingredients are to be determined carefully to prevent shrinkage and cracking after installation.

Additives of different type may vary the basic recipe and approach the performance of the screed the performance needs from time to time requests.

The height of the screed can be defined allowing, over and above the existing floor taken as a reference, adding half a centimeter in thickness of the tiles that you intend to put in place.

In commerce there are a large variety of products able to meet specific site requirements and to solve the problems that are most frequently linked to the leveling of the surface and the presence of moisture.

Autoleveled screed and lightweight screed

For indoors, when a minimum thickness is required and it is necessary to work quickly (within 30 minutes), Leca proposes Massettomix leveling, a premixed screed suitable for application even if there are floor heating systems.

Its fluid texture makes it easily leveled with a special bar as soon as it is thrown.

After 24-36 hours after laying the screed it can be walked on, allowing you to do other things with the pipeline, while for completion with a top layer of flooring is not sensitive to moisture it is necessary to wait up to two weeks.

When the thicknesses are greater you should instead prepare a screed consisting of two different layers, corresponding to two distinct working phases. For the lower one it can be used, in addition to the traditional blend, a lightweight aggregate having a cellular structure.

Leca again proposes one with zest clinkerized high resistance to mechanical stress and fire, with outstanding acoustic and thermal insulation.

Thanks to this property, located in completing the extensive application packet attic of flat roofs where, in accordance with the provisions of the current regulations regarding energy saving, you must respect a certain limit value of thermal conductivity.

The lightweight screed must however be completed by an upper layer adequately reinforced, and suitable to withstand the mechanical stresses induced by the various activities usually performed in the environment in which it is placed.

The completion can be constituted by a thin screed or self-leveling by a traditional cement and sand, suitably reinforced with networks consisting of various kinds of materials: steel, glass fiber or synthetic fibers.

During the restoration work of floors and foundations in existing buildings and in conjunction with changes due to the movement of bathrooms and kitchens, the substrate plays an important role.
From an assessment of its thickness it is possible to estimate the slope of the drain pipes and the new plant network.

It is important to highlight the fact that, as the thickness increases, is not to neglect the assessment of the load induced to the structure even in the presence of lightening layers.

Fast drying screed

Sometimes, however, the imperative of the construction site is set up a support, drying quickly, will prove adequate for moisture sensitive flooring such as parquet.

Fassa Bortolo proposes, to this end, a screed mixed ready for use, the SR 450, additivated with specific products able to shorten the drying time in work.

After about an hour and a half from the end of the processing is the taking of the slab, while the drying time is reduced to just 48 hours to an average thickness of 4 cm and a moisture content of less than 2%.

Retaining instead a mix for traditional screed you can decrease the drying time by adding specific products such as Mapecem by Mapei, hydraulic binder-setting and drying and, in addition, controlled shrinkage, especially suited to completion with finishes in wood, rubber and linoleum.