What should be the minimum thickness of a floor screed

The thickness of the floor screed is an important consideration when planning to install a new floor. For your flooring material to have a level and stable surface, this layer is necessary. Choosing the appropriate thickness guarantees longevity and averts future problems.

A floor screed’s minimum thickness varies based on the load it will support and its intended use. A thinner screed might be adequate for typical residential use, but a thicker layer is needed in commercial or industrial settings to support heavier loads. To ensure the longevity of the floor and prevent needless material costs, it’s critical to find the ideal balance.

What constitutes an appropriate floor screed thickness depends on a number of factors. These include the underlying substrate, the kind of screed that will be used, and whether or not underfloor heating will be incorporated into the screed. Taking the best possible outcome into account in each situation requires careful thought.

Comprehending the minimal prerequisites for floor screed thickness contributes to a flooring project’s success and longevity. By taking into account the particular requirements of your area and seeking advice from experts, you can lay a strong basis for your new floor.

Purpose of screed

Actually, screed is a subfloor that will later be used as a foundation for linoleum, laminate, parquet, or tiles.

Take note! To level the base rather than raise the floor level by, say, fifty centimeters, rough pouring is not necessary.

General requirements

Following these guidelines is advised when applying a floor screed:

  • At the stage of preparing the base, it is necessary to carefully seal all cracks and holes so that the lower floors are not damaged during the pouring process, since the mixture contains water.
  • Pouring is prohibited in rooms with a temperature below 5 ˚C, since failure to comply with this recommendation will lead to a decrease in its strength.
  • The density of the screed must be the same throughout the entire volume. Any cracks, chips and voids inside it are not allowed.
  • When laying over insulation, it is recommended to leave a gap of 20-40 mm between the fill and the walls, which is filled with insulating material.
  • Monolithic screeds are separated from the walls with a damper tape.

  • The final floor covering is laid only when the subfloor is completely dry (minimum drying time is 24 hours).

Counseling! The coating’s light gray color signifies that the mixture has fully dried.

  • SNiP allows that the subfloor may have deviations: for parquet, laminate, linoleum and self-leveling floors – up to 2 mm per 2 meters; for other types of coatings – up to 4 mm per 2 meters.
  • If the screed height is more than 40 mm, then reinforcement is required. In rooms where heavy loads on the floors are not expected, the absence of reinforcing components is allowed with a layer thickness of up to 70 mm.

A floor screed’s minimum thickness is essential to guaranteeing a sturdy, long-lasting, and level surface. Although the exact type and purpose of the screed will determine its thickness, a typical bonded screed should be at least 25–40 mm thick. For unbonded or floating installations, where they must endure greater stress and offer superior insulation, thicker screeds are frequently required. For the floor to last and function well, it must be the right thickness to avoid cracks, guarantee stability, and achieve a level finish.

Optimum screed thickness

The following variables determine the type, thickness, and necessary mixture composition of the floor screed:

  • the presence of unevenness and differences in the height of the base;
  • what exactly the mixture is poured onto (the floor slab, the insulation layer or the pipes – in the case of underfloor heating);
  • for which coating the surface is prepared;
  • features of the room (load on the floor, humidity, temperature, and so on).

Basic base

The thickness of the solution layer required increases with the severity of the irregularities and height differences. The floor screed’s minimum thickness, with minor flaws, will measure 20 mm. It is unnecessary to discuss the minimum thickness if you are dealing with significant changes (greater than 60 mm). There is a purpose to implement a solution in this instance, which will range in height from 100 to 150 mm and consist of a mixture of coarse sand, cement, and water.

Counseling! Crushed stone or expanded clay can be used as partial alignment to save money on concrete mixtures.

Do not fool yourself if you believe that you can tell the unevenness of the floor "by eye"—your eyesight might not cooperate with you in this regard. For this, it is preferable to use a special level.

Classification

Depending on thickness, there are three different kinds of screed.

The thin subfloor is the first kind. It is poured using self-leveling mixtures that let you build up to a 20 mm layer. Reinforcement is not necessary in this instance.

A screed that is up to 70 mm high is the second kind. In this instance, reinforcement in the form of reinforcement rods or a metal mesh is required.

The third kind is a monolithic layer with internal reinforcement that has a maximum thickness of 150 mm.

Composition of the mixture for the screed

Self-leveling mixtures work best for unevenness and height differences under 20 mm, as they enable the creation of a thin, even layer. You can immediately install the flooring on it once it has dried. Self-leveling mixtures disperse across the floor without assistance from a person. Among them are:

  • gypsum or cement;
  • fine-grained sand;
  • plasticizers that improve quality indicators;
  • glue;
  • pigments.

Take note! The manufacturer’s packaging specifies the minimum and maximum thickness of the screed of a particular composition.

One kind of self-leveling mixture that is applied to cement sand or a concrete base is called a bulk floor. This mixture is applied as a thin layer of screed ranging in thickness from 2 to 20 mm, or as a finish coating.

Counseling! It is advised that bulk floors have a thickness of no more than 20 to 30 mm; otherwise, they may crack over time.

Concrete’s relative affordability makes it an essential material for rough filling. The SNIP suggests the mixture’s composition as follows:

  • sifted sand;
  • cement;
  • gravel or crushed stone (fractions value from 5 to 15 mm);
  • water.

These days, lighter fillers with heat-insulating qualities are frequently used in place of gravel. The most widely used ones are polystyrene foam (granules) and expanded clay. The first is only utilized as a draft floor filler component, and the second is used as the finish. For the purpose of removing irregularities larger than 20 mm, mortar laying is done at a height of between 30 and 50 mm.

When there are notable variations (greater than 60 mm), coarse-grained sand is substituted for regular sand in sand concrete. Such a layer ranges in height from 100 to 150 mm.

When there is substantial base damage and the floor repair process needs to be expedited, a dry screed—made of materials that don’t need to be dried for a long time—is frequently created. It is composed of sheet material (such as plywood, chipboard, or gypsum fiberboard) on top of a layer of backfill material, such as expanded clay. Noise, heat, and hydro insulation is installed as needed. Such a "pie" can range in thickness from 35 to 60 mm.

Minimum thickness of floor screed

Two considerations are made when figuring out a floor screed’s minimum thickness:

  • what the screed is directly laid on (base base);
  • the composition of the mixtures (materials) used.

The minimum thickness for concrete screeds is 20 mm if the mortar is applied directly onto concrete slabs.

When screeding over bulk materials or solid heat-insulating products, the layer thickness cannot be less than 40 mm for heat and sound absorption. In this instance, metal mesh reinforcement is required. The waterproofing layer in the kitchen or bathroom should adhere to the same guidelines.

For pipeline coverings (heated floors included), SNiP advises that the screed’s thickness be ten to fifteen millimeters thicker than the pipes’ diameter.

According to SNiP, the cement and sand fill in areas meant for residential use should be thicker than 30 mm. It is acceptable to reduce the thickness to 15 mm when using premade polymer-cement mixtures. Regardless of the solution’s composition, a minimum 40 mm layer must be present if pipes are situated beneath the screed.

Naturally, you will spend less money if the screed is thinner, but as they say, "a miser pays twice." Some crucial points that are best considered are as follows:

  • when pouring a thin layer, water quickly evaporates, which may lead to cracking of the screed;
  • a minimum layer may provide insufficient adhesion to the base;
  • the possibility of damage to a thin screed from falling heavy objects.

Suggested Use! Plasticizers can be added to the mixture to lower the screed’s height while keeping its quality attributes.

Use Minimum Thickness (mm)
Residential floors 40
Light commercial floors 50
Heavy commercial floors 75
Industrial floors 100
Underfloor heating 65

For your flooring to be stable and long-lasting, a floor screed’s proper thickness must be used. It is generally advised that a minimum thickness of 50mm be used for most residential applications. This helps disperse loads uniformly across the surface and offers a strong foundation for flooring materials.

A thicker screed of about 75mm might be more appropriate for places where there will be more foot traffic or where large furniture and appliances will be positioned. This increased thickness lowers the possibility of damage or cracking over time and increases durability.

The exact specifications of your project will ultimately determine the appropriate thickness for your floor screed. You can make an informed choice that guarantees a sturdy and long-lasting foundation for your floors by taking into account elements like the type of flooring, the anticipated load, and the substrate’s conditions.

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Andrey Ivanov

Experienced civil engineer with more than 20 years of experience. Specializing in the construction of industrial and civil facilities. Author of many publications in professional journals.

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