PRODUCTION AND INSTALLATION OF CEMENTITIOUS SCREEDS
This technical specification refers to the installation of cementitious screeds on the reinforced concrete slab (base), intermediate layer or insulating layer between screed and base, to carry the final flooring without underfloor heating.
1. Relevant standards
EN 13318 (2000) Screed material and floor screeds - Definitions
EN 13813 (2002) Screed material and floor screeds - Screed material - Properties and requirements
EN 13892-1 (2002) Methods of test for screed materials - Part 1: Sampling, making and curing specimens for test
EN 197-1 (2011) Cement - Part 1: Composition, specifications and conformity criteria for common cements
and other standards mentioned in these standards.
Cementitious screeds can be made and installed from ready-made material that is delivered to the construction site in bags or by making it on the construction site.
The thickness of cementitious screeds should be in accordance with the architectural design and not less than 45mm and more than 80mm. For thicker and thinner screeds, the contractor should obtain the approval of the supervisor. The thickness of the screed, which is made of material that is mixed on the construction site, should be at least three times larger than the size of the largest grain of the aggregate.
According to the requirements for compressive and flexural strength, finished cementitious screeds should be classified in class CT-C35-F5 in accordance with EN 13813.
There are no special requirements for wear resistance and frost resistance.
For cementitious screeds for which a mixture of materials is prepared on site, the contractor should submit the recipe and method statement to the supervisor for approval before performing the works. Information on the main constituents of cement must be provided. The contractor is responsible for ensuring that the compressive strength and flexural strength of cementitious screed meet the above requirements.
Cementitious screeds should be reinforced with Q131 reinforcement mesh (wire distances 150x150mm, diameter of wire 5mm, for cementitious screeds with a minimum thickness of 50mm), welded wire mesh or polypropylene fibre. Fibres should be added to the screed mix in accordance with the manufacturer's instructions and screed recipe.
For the use of welded wire mesh, the consent of the supervisor is required.
The characteristics of the sound insulation layer should be in accordance with the architectural design.
The minimum thickness of PE foil under cementitious screed should be 0.2mm.
Before the start of work, contractor is obliged to submit manufacturer's certificates for all materials to the supervisor for approval, through the Submittal process.
If the walls in the room are plastered, they should be plastered to a concrete floor slab, before installing the cementitious screed.
Before starting the installation of cementitious screed, the contractor should mark the levels on the perimeter walls of the room with laser devices or surveying instrument.
When cementitious screed is installed over the sound insulation layer, the screed should be separated from the walls with a layer of the same material as the sound insulation, 1-2 cm thick. If cementitious screed is installed over an old concrete slab (when the project envisages screed which is bonded to the base), contact coating should be used for better adhesion. If the screed is laid without bonding to the base, PE foil should be placed under the screed.
The base for cementitious screed should be flat so that there are no oscillations in the thickness of the screed. If installation pipes are placed on the base, they must be firmly fixed to the base.
The temperature in the room where the cementitious screed is performed should be not less than + 5ºC.
The material for making the screeds must be mixed mechanically and taken out into the room mechanically, immediately after mixing, with rubber hoses (care should be taken that the rubber hoses do not damage other works). Excess material should be removed to the required level and then the screed carefully flattened and smoothed with a trowel machine (helicopter) Ø560 - 600mm. It is not allowed to spray water on the screed during smoothing. Post-treatment of the screed with cement is not allowed.
Flatness requirements: It is not allowed for the screed height to deviate from the designed level by more than ± 2 mm, with no more than 3mm variation in 2.0m.
Shrink joints in cementitious screeds should be cut (up to half the height of the screed) so that the size of the field does not exceed 40m2 and the length of the field 8m. Dilatation joints (cut along the entire height of the screed) must be made above the construction joints in a reinforced concrete base. In dilatation joints, the reinforcement should also be cut off.
The reinforcing mesh should be raised from the base (on the pads) so that it is in the middle zone of the screed.
During the curing period, the screed should be protected from air circulation and direct sunlight (not with foils) for at least 7 days. PE foils should protect the screed only from drying too fast at high temperatures (it is not allowed to wet the screed with water). It is not allowed to dry the screed by heating the room without the permission and control of the supervisor (in case the rooms are heated, the use of air dryers is recommended).
It is not allowed to walk on the screed for at least 3 days after the installation, unless otherwise stated in the method statement. Loading of construction materials and equipment is allowed after 7 days (if the screed is not fast drying).
4. Supervision and measurement of works
During the execution of the works, the contractor should make samples from the material delivered to the construction site for the installation of the screed in order to examine them in an independent laboratory for compressive and flexural strength. Samples should be 4x4x16cm or other dimensions required by the laboratory. Not less than three samples should be taken on a 500m2 of screed area.
After the completion of the works on the installation of screed, the level of the screed and flatness (with aluminium spirit level 2m long) should be checked. If major deviations occur, remedial measures, approved by the supervisor, should be applied.
Executed works are calculated per m2 of actually installed screed.
Please note that the technical specifications on this web site are templates only, information provided should be carefully checked and aligned with your project needs.
CT - cementitious screed
C35 - compressive strength after 28 days min. 35N/mm2 (Mpa).
F5 - flexural strength after 28 days min. 5N/mm2 (Mpa).
Cementitious screeds with compressive strength C20 or C25 are used mainly in residential buildings.
According to EN 197-1 cement CEM I is pure Portland cement, and CEM II cements with additional letter designations are Portland-composite cements with the addition of other single constituents (limestone, shale, blast furnace slag, etc.) and are in principle suitable for the manufacture of cementitious screeds. Cement can be strength classes 32.5, 42.5 or 52.5.
The cement content in cementitious screeds is usually 300kg/m3.
The weight of Q131 mesh is about 2.12kg/m2, mesh should be made of steel with a tensile strength ≥500 MPa.
The weight of welded wire mesh (wire distances 50x50 mm, diameter of wire 2mm) is about 1kg / m2.