Concrete for screed: the device base of the subfloor.

In this article, we will talk about how to prepare lightweight concrete for screed and how to apply it for its intended purpose. In addition, we consider the main advantages and disadvantages that should be considered when choosing and using such building materials.

Cement Mortar Structure

The choice of material for the device foundation subfloor

According to statistics, the base of the floor in most construction sites is made using cement-containing mortars.

Materials made of Portland cement and quartz sand are practical, easy to prepare and to use.

But, unfortunately, cement mortar in standard proportions has several disadvantages, due to which its use as a base for sub-flooring is undesirable.

  • It is known that classical cement-sand mixtures are widely used in arranging screeds over 5 cm thick. But such materials are heavy. This deficiency can cause serious problems if the foundation of the floor is not in the house on the ground, but over the ceiling in a high-rise building.
  • An ordinary concrete screed weighs over 20 kg per meter, provided the layer is 1–1.5 cm thick. This is really a lot of weight, but it can be reduced by adding porous aggregates to the mixture.
  • Moreover, the standard proportions of concrete for screed imply the need for additional floor heating, as the finished coating itself will be cold.
  • Again, porous aggregates come to the rescue of this problem. The calculation of concrete on the screed shows that the addition of such ingredients can significantly reduce the degree of thermal conductivity of the material.

Important: Good results are shown by foam concrete screed. But to prepare such a mixture in the domestic environment is not easy, as pore-forming additives to purchase in the market is problematic.

From the above, we can draw the following conclusion. For the construction of the base of the floor in a residential area, light mixtures based on Portland cement with the addition of such aggregates as expanded clay, perlite, polystyrene, etc. will be the optimal solution.

Distinctive properties of lightweight concrete structures

Light solutions used in the manufacture of screeds, have several advantages in comparison with conventional cement-sand mixtures.

  • More affordable price;
  • Low weight (1.5 times less than the mass of ordinary concrete);
  • Short time setting and strength;
  • Low thermal conductivity;
  • High degree of noise insulation;
  • Easy cooking with your own hands.

Features of the preparation of lightweight concrete

In the photo - the preparation of the solution in the mixer

On large construction sites used concrete for dry screed. As a result, the arrangement of the subfloor is performed in a short time without compromising the quality of the finished result.

In the case of light concrete in individual construction is still easier. The material for pouring the base is made directly at the construction site, and only the usual agitator is required from the equipment.

As already mentioned, it is necessary to add porous aggregates to the classical solution of cement, sand and water and thus reduce the consumption of concrete by 1m2 of screed. In the manufacture of such solutions, water is added in small quantities, sufficient to give the mixture the plasticity required during the installation.

So, after we have decided on the choice of building materials, consider the characteristics of the used aggregates.

Types of aggregates for light solutions

The use of special aggregates can reduce the consumption of concrete by 1m? screeds without sacrificing strength properties.

Among the porous additives, we note the following types of fillers:

  • Керемзит - oval granules with a porous structure. The material is made with different sizes (fractions).
On the photo - expanded clay granules

The production of expanded clay is carried out using clay, which is burned at temperatures above 1 thousand degrees.

The volume weight of the finished aggregate is from 250 to 600 kg per 1m ?. When claydite is added to the cement-containing solution, a fundamentally new material is obtained - keramsit concrete. The weight of such a mixture at the rate of laying a layer with a thickness of 1 cm does not exceed 18 kg per 1m ?.

  • Vermiculite - natural mineral with a layered structure. If vermiculite is heated to certain temperatures, threads of silver are formed. The threads have a high tensile strength, which allows them to be used in the manufacture of light and at the same time very strong concrete.
On the photo - expanded vermiculite

Expanded vermiculite, commonly used in construction, is characterized by a high degree of water absorption (100 g. Of aggregate absorbs up to 400 g. Of water), and therefore, when mixed with cement mortar, it forms an almost homogeneous consistency.

This property has a positive effect on the strength of the finished screed. In addition, the finished base of the floor, made with the addition of vermiculite, is characterized by extremely low thermal conductivity and high sound insulation.

  • Perlite - a rock of volcanic origin.
On the photo - perlite granules

For use as a building material, perlite is heated to temperatures in excess of 1 thousand degrees. The result is a swelling of the granules with the complete removal of water from them.

Perlite, ready to use, looks like fine crushed stone. The material is distinguished by its low weight and excellent heat and sound insulation qualities.

Recommended aggregate fraction

Proper selection of the size of the granules - a pledge of strength of the finished material

Compliance of the aggregate fraction with the technological standards is a very important point that should be taken into account when making light mortars for pouring the base of the floor. The fact is that the larger the fraction, and accordingly the area of ​​the aggregate granules, the lower its compressive strength.

Of course, the wrong choice of the fraction of granules will negatively affect the strength of the finished concrete screed.

The fraction of aggregates for the independent production of the mortar for subsequent flooring is as follows:

  • expanded clay - from 5 to 10 mm (a fraction of 20 mm is used for the device of two-layer screeds);
  • vermiculite - from 0.6 to 2 mm;
  • perlite - up to 15 mm.

Important: Materials with the specified fraction should be used with a degree of moisture less than 10%. For this, the filler is recommended to dry before use.


Now you know what the instructions for preparing the solution for pouring the subfloor subfloor are. You can find more useful information by watching the video in this article.

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