A screed is a rough floor, the upper part of its base, which serves as the basis for the finishing coat. Screed not only creates the most even surface for the future final finish, but also guarantees the strength and durability of the entire floor in the apartment. The thickness of the screed is of great importance: too thin a layer will not provide sufficient strength, too thick entails unjustified waste of materials.
There is no universal fill thickness indicator for an apartment; in each case, this parameter differs depending on the following conditions:
- type and condition of the base, material on which the screed is laid;
- materials used for subfloor installation;
- operational characteristics of the premises;
- selected finish.
Why is it necessary to calculate the minimum screed thickness?
The desire to reduce the layer of leveling material is correct not only in terms of savings and reducing the cost of repairs in the apartment. Here are a few more reasons why you should avoid the “thicker is better” principle when working with a rough coat.
- Too thick a layer of coating reduces the distance from floor to ceiling.
- Exceeding the height of the layer above the warm floor reduces heat transfer and increases the energy consumption spent on heating.
- Neglect of existing norms can lead to an emergency situation, for example, a balcony ceiling may not withstand a too thick and heavy layer of concrete.
- The thicker the screed, the longer it dries.
- Too thick a layer of material can, when expanding, act on the walls, causing them to deform.
Tip: in order to avoid negative consequences from the thermal expansion of the screed material, before pouring the mixture, it is necessary to paste over the walls around the entire perimeter of the room with a damper tape.
What determines the thickness of the floor screed?
Consider separately all the factors affecting the thickness of the rough coating.
Base
The thickness of the screed depends on the degree of unevenness of the base. The greater the slope and height differences, the thicker the layer of material will be needed.
If it is required to level the base with minor flaws, the minimum thickness of the floor screed in accordance with the norms of SNiP should be 2 centimeters. However, it must be borne in mind that in this case reinforcing elements must be present in the fill, too thin cement-sand screed will crack sooner or later.
Leveling compounds that do not contain any additional reinforcing additives should be laid in a layer of 4 cm. self leveling compounds. The minimum allowable layer thickness for such mixtures is small, depends on the specific composition and is indicated on the packaging by the manufacturer.
In the event that significant differences in floor height are observed in the apartment, which may occur due to insufficiently high-quality laying of floor slabs, we can no longer talk about the minimum layer. In such a situation, sand concrete containing coarse sand is often used. Sometimes the surface irregularities are so great that when they are leveled solely by pouring, its maximum thickness can reach 15 centimeters. Experienced builders know the secret to reducing mix costs: Partial leveling can be done with expanded clay or crushed stone, due to which it is possible to reduce the layer of concrete pouring.
The presence of an insulating layer
The thickness of the screed will also depend on whether it is done directly on the floor slabs, or additional sound or waterproofing materials are used.If you lay the mortar directly on concrete slabs, then the minimum layer for cement-sand or concrete mixture will be 2 centimeters. If an insulating layer is used that prevents the adhesion of the screed to the base, its thickness should not be less than 4 centimeters. Such requirements are clearly spelled out in the rules of SNiP.
Material used for screed
Semi-dry mixes
The minimum thickness of the cement screed, which is still the most popular, should be as follows:
- when using a mixture with the addition of various plasticizers - not less than 3 centimeters;
- when performing work with a cement-sand mixture without additives - from 4–5 centimeters;
- using reinforcing mesh - 3 centimeters.
Important! Keep in mind that after a rough layer of concrete or cement, special mixtures for finishing screed are usually additionally used. The exception is the floor under the tiles, where the tile adhesive performs the final leveling function.
self-leveling floor
The so-called bulk floor, for which self-leveling mixtures are used, allows you to achieve the thinnest layer - from 2 millimeters. This option is suitable for a fairly flat surface; any material can be laid on the self-leveling floor: tiles, laminate, parquet or linoleum.
Important! There are limitations for the self-leveling floor - the maximum thickness should not exceed 2-3 centimeters, otherwise the coating will crack over time.
Dry screed
A “dry” technology screed is done in cases of serious damage to the surface of the base, when choosing a tree as a finishing coat or to speed up the repair process in an apartment - there are no materials that require long drying. Immediately after the completion of the creation of the subfloor, you can lay tiles or any other selected coating. Thickness dry screed, made according to the KNAUF system, can start from 3.5 centimeters, of which 2 centimeters fall on sheet material (chipboard, plywood, GVLV). The rest is a layer of backfill material, which is most often used as expanded clay. If it is necessary to achieve good indicators of noise, hydro and thermal insulation, the expanded clay layer should be more than 4 centimeters, which means that the thickness of the entire “pie” should be at least 6 centimeters.
Warm floor
O screed for underfloor heating it is necessary to speak separately, since in this case, in addition to leveling the floor, it has the additional function of a heat distributor. In this case, the main condition that concerns the thickness of the fill is the high-quality concealment of the heating elements. If standard pipes with a diameter of 2.5 centimeters are used when arranging a warm water floor, then the total thickness of the screed will start from 5 centimeters. The minimum layer of material above the pipes is 3 centimeters. In this case, experts recommend not saving and not striving for a minimum indicator, since with a small thickness of material above the pipes, the floor surface will warm up unevenly. Too large a layer exceeding 5 centimeters is also not appropriate, since most of the thermal energy will be spent on heating concrete. The best option would be a layer thickness of 4 centimeters above the pipes. For electric underfloor heating, the minimum overall layer should not be less than 3 centimeters.
Purpose of the premises
When choosing the thickness of the subfloor, you need to keep in mind the load on the floor covering in the room where the repair is being carried out. In the apartment, the greatest mechanical load falls on the floors in the corridor, bathroom, kitchen, and hall. In these rooms, you should not be limited to the minimum possible layer and make a fill from 5 centimeters thick.
Why can't the screed be too thin?
You can save on materials for the screed by making it as thin as possible, but you need to keep in mind a few important points:
- Too little layer due to rapid evaporation of moisture can lead to cracking or poor adhesion to the substrate.
- A thin screed can be damaged if massive objects fall on the floor.
- Insufficient fill thickness during the installation of underfloor heating will not be able to ensure high-quality heat distribution.
Tip: you can reduce the thickness of the screed without loss of quality by adding plasticizer substances to the solution. For these purposes, you can use tile adhesive, PVA, detergents and lime.
