According to their type of production, screeds are divided into construction site screeds and prefabricated screeds.

In contrast to precast screeds, construction site screeds are produced on site, using screed mortar - which is mixed on the construction site or delivered in the form of dry or fresh mortar - or mastic asphalt. They are designed heated or unheated and are divided into composite screeds, screeds on separation layer and floating screeds according to their structure. Construction site screeds either serve as a substrate for the final floor covering or, as a so-called useful screed, represent the finished floor surface itself.

CT - Cement screed

CTF - Cement flowing screed

SR - Synthetic resin screed

MA - Magnesia screed

CA - Calcium sulphate screed

CAF - Calcium sulphate flowing screed

AS - Mastic asphalt screed

In contrast to construction site screeds,prefabricated screeds, also known as dry screeds, are delivered to the construction site and laid as finished slabs. The elimination of the drying phase on the construction site leads to a much faster readiness for covering and no larger quantities of moisture are introduced into the building. Lower construction heights than with construction site screeds are also possible. Prefabricated screeds can also be combined with underfloor heating in some cases. As a rule, they are the substrate for the final floor covering, but there are also products that can serve as a finished floor surface themselves.

More about construction site screeds

In addition to the classification of construction site screeds according to their binder according to the above table, they are also differentiated according to DIN 18560 according to their method of installation:

Screed/ heated screed on insulation layer (floating screed) according to DIN 18560-2:

The screed pane is completely decoupled from adjacent components on the underside and at all lateral connections, it "floats", separated by a separation layer, on an insulating layer that can meet impact sound and thermal insulation requirements. In combination with edge insulation strips, the insulation layer causes a significant reduction in airborne and structure-borne sound transmission to rooms adjacent to or below the sides. This type of installation is carried out if there are heat or sound insulation requirements for the floor structure, or if the screed serves as a heat transfer surface for underfloor heating, e.g. in public buildings, residential or commercial buildings. [...]

Composite screed according to DIN 18560-3:

Composite screed form a force-fit connection with the load-bearing substrate and can thus be designed to be highly resilient and thin at the same time. They are particularly suitable for industrial construction, for the economical production of heavy-duty surfaces, when the screed does not have to meet any requirements for sound or heat insulation. They are also used in exceptional cases during renovations when there is not enough construction height available to form a floating screed and the significantly reduced noise insulation values can be accepted. In contrast to the other types of installation, composite screeds do not necessarily have to be produced in the same thickness throughout and are therefore also suitable as sloping screeds for the formation of surface slopes on horizontal substrates. [...]

Screed on separation layer according to DIN 18560-4:

Screeds on separation layer are similar to composite screeds are particularly suitable for applications in industrial buildings if the screed does not have to meet any requirements for sound or thermal insulation. An advantage over composite screed is the possibility of arranging a vapour barrier or waterproofing (e.g. according to DIN 18195) between the load-bearing substrate and the screed. Even in the case of substrates that are not sufficiently rigid, e.g. made of steel or wood, it may be necessary to install a screed on a separating layer instead of a composite screed. [...]

Notes on planning

sound insulation and thermal insulation: A significant improvement in thermal and/or sound insulation can only be achieved in construction site screeds with a screed or heating screed on an insulating layer. If there are requirements for impact sound and thermal insulation at the same time, two insulation layers are usually arranged below the screed pane: pressure-resistant thermal insulation and impact sound insulation with defined compressibility. The use of combined thermal and impact sound insulation is only possible to a limited extent, as the degree of compressibility increases with increasing insulation thickness. However, according to DIN 18560-2, this is only permissible to a limited extent:

a maximum of 5 mm (for payloads as individual loads up to 2.0 kN² and surface loads ≤ 3 kN/m²) or
maximum 3 mm (for higher single/surface loads and generally for mastic asphalt screeds).

The strength of the impact sound insulation is given with two values, e.g. "45 – 3". The first number denotes the delivery thickness dL (here: 45 mm) and the second the compressibility C under load (here: 3 mm).

When selecting suitable insulation materials, their usability must be ensured, taking into account all relevant boundary conditions (e.g. screed installation type and material, fire protection requirements, traffic load, material incompatibilities with the substrate, 250 ° C installation temperature of mastic asphalt, binder/solvent resistance in synthetic resin screeds). Depending on the material , the insulation materials must meet the requirements of DIN EN 13162, DIN EN 13163, DIN EN 13164, DIN EN 13165, DIN EN 13166, DIN EN 13167, DIN EN 13168, DIN EN 13169, DIN EN 13170 or DIN EN 13171. In addition, for thermal and/or sound insulation requirements for floating screeds, the suitability must be proven in accordance with the building regulations, e.g. via relevant application standards such as DIN V 4108-10.

If there are requirements for the screed in terms of sound or heat insulation, the usability of the screed mortar or screed compound must also be proven. Either by declaring compliance with DIN EN 13813 (thermal insulation) and/or with the DIN 4109 series of standards (sound insulation) by the manufacturer, or by proving the required properties by means of a product-specific proof of usability, e.g. a general building authority approval (abZ).

Heated screeds: According to DIN 18560-2, the following types of heating screeds are distinguished:

Type A: the heating pipes are located in the screed above the insulation layer (wet-laid systems). Design advantage: particularly good heat dissipation to the surrounding screed.
Type B: the heating pipes are located in the insulation layer below the screed (dry-laid systems). Design advantage: particularly easy creation of movement joints in the screed disc, thinner screed disc than with type A.
Type C: the heating pipes are located in a levelling screed below the screed, between the levelling screed and the screed there is a separating layer (wet-laid systems).

In type A construction, flowing screeds are particularly suitable as heating screeds, as their very dense structure enables optimal heat transfer between the heating pipe and the heat transfer surface (screed).

Approved systems are common that include the impact sound insulation and the heating pipes, including the fastening, and which are completely laid by the heating engineer.

Further requirements for heated screeds, e.g. for necessary pipe coverings, can be found in DIN 18560-2.

Usable screeds: If the screed surface also represents the finished floor surface, it is called a utility screed. In principle, all types of screed are suitable for this purpose. Various properties can be assigned to the floor surface, e.g. increased surface hardness due to the addition of hard material to cement-bound hard screed or colour designs to solid-coloured exposed screeds. Utility screeds are widely used in industrial construction, but they are also suitable for public buildings, administrative buildings or residential buildings. High-quality surfaces can be achieved by sanding the screed surface, if necessary several times with increasingly finer grain.

Sanding screeds can also be a design renovation option for existing buildings, as an alternative to a new floor covering.

Terrazzo floors are a particularly high-quality form of sanded floor screed. By directly applying decorative aggregates, which differ in their colour and/or grain size, for example, decorative patterns can be incorporated into the screed surface. The surface must be finely sanded to such an extent that the largest grain used is visible. Regulations for the execution of terrazzo floors are contained in DIN 18353 (VOB C).

Heavy-duty (industrial) screeds according to DIN 18560-7: DIN 18560-7 applies to particularly high-stress screeds, especially in the industrial sector, in addition to the other parts of the DIN 18560 series of standards. Mastic asphalt screed, synthetic resin screed, magnesia screed and cement-bound hard material screed are suitable as highly durable screeds, this is a cement screed with a particularly hard surface due to the addition of hard materials according to DIN 1100. Depending on the type of tyres used by industrial trucks, particularly stress-intensive work processes and the frequency of pedestrians, the screeds in Table 1 of DIN 18560-7 are assigned to load classes I (heavy), II (medium) and III (light). In some cases, this results in deviating specifications from Parts 1-4 of DIN 18560, e.g. with regard to nominal thickness, flexural tensile strength class, surface hardness and composition or design of the screed.

Fire protection: According to DIN 18560-1, the assignment of the fire behaviour of screed mortars and screed compounds to a class according to DIN EN 13501-1 is an important prerequisite for their use. Cement screed mortars, calcium sulphate screed mortars and magnesia screed mortars generally comply with fire behaviour class A 1 (Afl) according to DIN EN 13501-1 (= non-combustible) if their mass fraction of organic substances is no more than 1%. For all screed mortars and compounds, the fire behaviour class must be indicated by the manufacturer on the product.

This becomes important, for example, if the proof of usability of a fire door specifies specifications for the execution of the floor structure in the door area, if, for example, no combustible building materials may be carried through below the door. In this case, the entire structure (screed, insulating layers, separating layers, edge strips, floor covering) must be checked to see whether the intended materials allow installation in the area of the door.

Joint formation: A distinction is made between the following types of joints in the case of screeds:

Movement joint
Apparent joint Working
joint Edge
joint According

to DIN 18560-1, the building planner is obliged to draw up a joint plan that contains the arrangement and type of all joints to be provided for in the screed. The reason for this is that the screed trade cannot only predict the type and arrangement of all joints, as these can also become necessary due to the boundary conditions of previous (shell construction) and subsequent (floor covering) trades. In addition, design aspects can also be taken into account in the joint arrangement. In the case of heated screeds, the heating circuits and screed fields must be coordinated with each other, and there must be no intersections of movement joints and heating elements. Heating connection pipes that cross movement joints must be protected, e.g. by approx. 30 cm long pipe sleeves.

Since the type of floor coverings (rigid/elastic) can also have an impact on the necessity/arrangement of screed movement joints, these must be determined at the time of preparation of the joint plan. The joint plan should be part of the service description for the screed trade.

Building joints (which absorb movements of the shell) must always be adopted into the screed pane in the width of the shell joint, regardless of the type of construction and the material of the screed. Movement joints of the screed must always be adopted in the later covering.

Movement joints may also be necessary for sound insulation reasons (as a separation joint), e.g. if a partition wall is to be erected on the finished screed. The sound insulation between the two rooms is significantly improved in terms of airborne and structure-borne sound transmission if the screed along the partition wall is continuously interrupted by a separation joint.

In door passages, movement joints must usually always be provided for heated screeds, especially if the rooms are at different temperatures (e.g. door between bedroom and bathroom). Also for sound insulation reasons, a separation can be useful/necessary here.

Source: bauwion