Expansion joint in concrete: the need for use and

In this article we will discuss what are expansion joints in concrete floors and similar structures and why they are needed. We will also consider the main types of these structural elements and how to implement them.

Anti-distortion seams - versatile with a wide range of applications

The main features and the need to use

In the photo - filling the cavity of the seam with silicone sealant

For experienced builders, the tendency of concrete to crack during the drying phase is not a secret. But it turns out that the tendency to cracking persists in the course of the subsequent operation of the finished object (find out here how to pour concrete steps yourself).

Such processes can be triggered by temperature and shrinkage expansion of the material. And if we do not promptly compensate for the stresses that arise, the destructive process will negatively affect the condition of the entire structure.

Proper and timely arrangement of expansion joints in concrete floors allows minimizing the negative impact of temperature and shrinkage expansions and thus ensure a long-term service life for a construction object or structure.

Statistics on the use of structures equipped with seams shows that they are able to withstand such factors as:

  • temperature fluctuations;
  • shrinkage processes;
  • changes in moisture content in ambient air;
  • chemical reactions in the floor;
  • creep concrete.

Expansion joints are a prerequisite for the organization of monolithic concrete floors and according to construction standards are used if:

  • the floor has a complicated configuration;
  • the area of ​​the screed is more than 40 m ?;
  • one of the sides of the room in length has more than 8 m;
  • floor temperature during operation is higher than necessary.

Expansion joints in concrete according to the SNiP are located:

  • near doorways
  • along the perimeter walls;
  • in the joints of the floor and other concrete structures.

Types of commonly used seams

Layout of separation elements in a room with columns

The following types of expansion joints are most commonly used:

  • shrinkage;
  • insulating;
  • constructional.
In the photo T-shaped structural seam

Let us consider in more detail the features of each of the above categories:

  • Shrinkage seams;

Concrete coating hardens and dries unevenly, that is, the top layer dries out faster than the bottom. As a result, the level of the screed on the edge is slightly higher than in the center.

This is a natural process, but the resultant stresses and, as a result, the formation of cracks become its result. Shrink seams allow the prevention of such consequences.

The seams are cut to a depth of 1/3 of the thickness of the concrete screed. Cutting is done immediately after finishing the coating finish. On an industrial scale, cutting is done by means of a joint cutter with the function of water irrigation of the cutter.

Important: When performing such works with your own hands, at the stage of average moisture content of concrete, slats of the required dimensions are installed, which can later be removed and get the seam of the desired shape.

  • Insulating seams;

This type of expansion joint is used in concrete structures in order to prevent the transfer of deformations to the screed from major architectural structures.

Elements of this type are located mainly around the perimeter of the foundation around the columns and along the walls. In this case, no joint cutter is used. Special elastic insulation material, the price of which is low, fits along the line of the future weld before applying the concrete solution.

  • Construction seams;

This type of demarcation applies if a break is taken during the laying of the screed. That is, the seam connects the previously laid and subsequently applied layers of concrete.

The shape of this separating element is complex and resembles a thorn-groove connection in cross section. The arrangement does not use a joint cutter, and work is carried out mainly on wet concrete using slats.

The distance between the seams

On the photo - compensating gaps in the floor screed laid by yourself

Температурно-усадочные швы применяются для ограничения напряжений, но для того чтобы они эффективно выполняли свою функцию нужно правильно рассчитать их расположение и прежде всего расстояние друг от друга (см.также статью «Делаем бетонные ступени для лестницы»).

In accordance with generally accepted standards, the distance between the separation elements should be no more than 150 meters for buildings of heated type based on prefabricated structures and 90 meters for buildings erected using monolithic and prefabricated monolithic structures.

Important: If the building is not heated, then the declared distance between the expansion joints in reinforced concrete should be reduced by 20%.

Sealing of separation elements

Scheme of industrial sealing of gaps

At sites with increased requirements for the hydrophobicity of floor screeds, there is a need to seal joints.

This is explained by the fact that excessive moisture, falling into the cavity of the separating element, contributes to the gradual peeling of coatings. Moreover, the destructive process becomes more intense with increasing air temperature in the room.

By performing a timely sealing, you can prevent the negative effects of excessive moisture. In addition, properly performed sealing prevents the likelihood of clogging of the joint cavity.

The important point is the choice of sealant. In this case, it is necessary to take into account the operating conditions and loads exerted on the concrete pavement.

Among the commonly used sealants, the following compositions should be noted:

  • silicones
  • polybutylene mastic;
  • hot and cold curing thermoplastics based on bitumen or butyl rubber;
  • thermoreactor based on polyurethanes, vinyl acetates and polysulfides.

It should be borne in mind that floor coverings, within industrial facilities, must not only be easily cleaned of contamination by means of dry and wet cleaning, but also withstand substantial mechanical loads.

Taking into account the requirements for such floors, it can be assumed that the sealant must be both hard enough to withstand the load, but also elastic to prevent the formation of chips.

Independent device of a waterproof deformation seam

Seam in the screed, filled with sealant and covered with cement mortar

Consider how, using diamond drilling of holes in concrete, you can make a separating element on an already dry screed.

  • At the first stage with the help of shoelaces or a long plastering rule a line is drawn, along which we will cut the grooves. On average, the width of the ditch should be 20-30 cm, and a depth of 3-4 cm.
  • After you have done all the necessary markup, we cut the concrete with a wall chaser, setting the cutter to the desired depth. Considering the fact that cutting of reinforced concrete with diamond circles is performed on a small width, we cut several gates. We cut down the concrete with a perforator, trying to make it as even as possible.
  • In the middle of the lay out a temporary profile, for this fit even slats up to 5 cm wide or aluminum profile, which is used when installing drywall.
  • On both sides, the profile is poured with concrete. After about 1-2 hours, the profile is dismantled.
  • After the concrete is completely dry, the resulting gap is filled with sealant and smoothed.


Теперь вы знаете, какова инструкция устройства разделительных швов, также вы получили общее представление о том, как справиться с этой работой самостоятельно (читайте также статью «Железобетонные ступени: нормативные документы и особенности монтажа»).

If you have any questions, you can find the answers to them by watching the video in this article.

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