Home Article Is it necessary to screed under a warm floor

Is it necessary to screed under a warm floor

How Long Should You Wait Before Waterproofing Over Screed?

What do you need a screed for underfloor heating?

Screed for underfloor heating is used in the process of installing the heating system to level the surface. A layer of concrete covers the pipes and fills in all the areas between the coils. Thus, the entire system is inside the concrete screed. As already mentioned, it protects it reliably and reduces heat loss in the process.

By adding a special plasticizer to the mixture, air bubbles will be recycled from the concrete, resulting in a very dense screed. The outer layer of screed is the basis for a decorative floor covering.

Screed under a warm water floor not only well protects the pipeline from all kinds of damages, but also contributes to an even distribution of heat over the floor surface. It also supports the heat and sound insulation of the lower slabs.

The thickness of the screed over the water heated floor. Materials for the substrate

screed, warm, floor

On a rough base is laid a layer of polyethylene foam, which can withstand heat up to 900 degrees

In the arrangement of the base of the water floor experienced builders act as follows:

  • A special substrate of extruded foam polystyrene is laid on the rough base.
  • A lavsan film (vapor barrier) is installed on it.
  • It is closed with a layer of foil.

The last of these components is needed to distribute the heat evenly over the entire floor in the apartment.

A good substitute for such a substrate. foam or extruded polyethylene, which is not inferior in its characteristics of polystyrene foam. The distinguishing features of the latter include a very low thermal conductivity, in which it is inferior only to mineral wool coatings. The screed for water underfloor heating on top of the insulation layer turns into a heating monolith of considerable area.

Since polystyrene, as well as polyethylene can withstand heat up to 900 degrees, water pipes are laid directly on the floor foundation without harming the insulating material. In the manufacture of warm floors on the interpanel slabs are taken plates of polystyrene foam thickness of about 20-30 mm. On the first floors of buildings located directly above the foundation, as a base is allowed to use foam plastic. This will require plates with a thickness of at least 100 mm. Other materials that, according to SNIP, are allowed to use as a substrate:

The choice of the specific material is determined by the current state of the subfloor and the type of flooring to be laid on it.

What is the thickness of the screed for water and electric underfloor heating and how to make it

Nowadays underfloor heating is more and more often chosen as additional or sometimes the only heating. Such a heating system is economical, convenient and allows you to achieve an optimal temperature in the room. There are many master classes on laying a warm floor and home master, armed with instructions and advice from professionals, it is quite possible to do the job yourself. Remember, however, that for the heating system “Underfloor heating” it is important to properly make the screed. Its arrangement. one of the most labor-intensive stages in the laying of warm floors.

Which underfloor heating is better?

If you really hope to find an answer to the question of which floor heating is better in the screed or under the tile, you are unlikely to come to an unambiguous conclusion. Each of them has its pros and cons. Let’s look at the features of underfloor heating systems in more detail.

Modern homeowners no longer need to convince in the advantages and expediency of using warm floors. Additional heating systems designed to create a more comfortable environment in individual rooms, and electrically heated floors as an alternative to traditional forms of heating are firmly in the home. Rare home renovation can do without the installation of warm flooring in at least one room, kitchen, bathroom, hallway or a closed balcony.

Given that there are currently several technical solutions for underfloor heating systems cable systems in the screed, heating mats and thin infrared film structures, potential buyers are trying to figure out what is better to use in one case or another. In addition, it is difficult to determine the best way to install in screed, under the parquet, tile, laminate, or directly under the soft floor covering? To correctly answer this question, you need to carefully examine the purpose, permissible scope of use, as well as the pros and cons of all the above-mentioned floor heating systems and methods of installation.

Option 2. CPS

Cement-sand screed floor heating is performed on the technology of the floating floor, based on a solution of cement, sand and water with the addition of plasticizer and fiber, or based on ready-made dry mixtures.

Important! Plasticizer and / or fibers are mandatory in the screed of the floor heating.

  • If you do TP in the house, for the preparation of CPS mortar it is enough cement of grade M200. Clean sand is needed. The proportion of sand/cement, 3/1 (three sand-one cement).
  • If the floor is made in a garage, the brand of cement is taken above from M300 to M500, ideally M400.

Required element in the grouting of CPS, are fibers of reinforcing fiber and plasticizer. Fibre is added in amount of 900 g. per cube of mortar. Fibre plays a reinforcing role.

Important! Plasticizer (this is not fiber) is added to any type of DSP floor heating. It (plasticizer) compensates the thermal expansion of the warm floor, protecting the CCCP from cracking.

CCCP TP screed is separated from the base of the floor. For what a layer of polyethylene with thickness of 200 microns is laid on the base. For better heat dissipation, a layer of thermal insulator, 20 mm thick, is placed under the screed. Important! A foil substrate is not an insulator.

Important! To ensure trouble-free operation of the floor heating, the floor heating screed must only be laid on an even, firm base. Base irregularities can lead to the formation of air cavities that can shrink under load. If the base of the floor is uneven, under the screed of a warm floor, you need to make an additional alignment screed.

Cemented screed is separated from the walls of the room, for which around the perimeter of the room is fixed damping tape or strips of any solid insulating material 5-10 mm.

Floating screed TSS necessarily reinforced with a mesh mesh 10 x 10 cm. Reinforcing mesh not only holds the screed itself, preventing it from cracking during drying and operation of the floor heating, but also serves as a base for fixing the water floor pipes and cables of the electric floor. It is important to ensure that the mesh is lifted 10 mm from the foil.

The thickness of the layer of screed, in the version of the cement-sand screed without fibers with a reinforcing mesh, can not be less than 10 cm. This is the kind of layer that will ensure the formation of a solid floating slab. In this case, the thickness of the screed must provide cover pipes (cables) with a layer of at least 30 mm, otherwise there will be strip heating of the floor.

Ready mixes will simplify the work

There are many manufacturers producing ready-to-use mixtures (leveling agents), including those suitable for underfloor heating ties. The solution of such a mixture is made by adding water in the proportion indicated on the package. The screed can be installed with or without screed, depending on the brand and manufacturer.

The use of ready-made mixes, the best option for self-construction of screed warm floors.

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Nuances of the test check

When making wet screed of the concrete or cement-sand mixture hired gang should not be in a hurry and immediately pay for their services. Wait for the artificial stone to cure completely. And the first 2 weeks the surface is covered with a film, periodically wet with water to maximize moisture.

Then you need to wait a while, which is about a month, so that the composition, which has covered the pipes of the warm floor, crystallized. The term depends on the thickness of the layer. it is an individual figure for each case.

Once the allotted time for curing has expired, you can carry out a revision of the surface, arrangement of which was engaged in the hired team. There are some nuances that should be checked when receiving their work.

When inspecting must pay attention to each section of the screed in all rooms. the presence of luster is undesirable, the top layer should be flat, evenly gray, no chips and cracks.

Then the flatness of the surface is checked with a two-meter rod. a rule. It is applied in several places to the screed. Norm if the gap does not exceed 4 mm. This SNIP 3.04.01-87, Table 25.

For tapping it is better not to take a hammer, and the end of a wooden bar and tap. The whole surface is checked. the sound is the same, ringing. If deaf, then there are delamination of the screed from the base.

If the surface has passed the test with flying colors, you can accept the work and pay the crew a fair wage. If it is the result of independent work, you can be proud of it.

Now all that’s left is to conduct thermal tests. It is important to remember that they are launched after a month, not before. Start at 25 with a daily increase in temperature by 5 degrees until it reaches the design value, not forgetting to monitor the pressure loss.

Rules and examples of calculations of a hydronic underfloor heating system can be found here. with useful systematic information.

Requirements for the screed

There are no special standards and requirements. It is important that the entire surface is perfectly flat. This will allow the underfloor heating system to work correctly. Above all, cracks must be avoided. This may indicate a violation of the base casting process or a mismatch of all components. Also on the formation of cracks may affect the thickness of the screed over a warm floor. Let’s talk about this in detail.

First of all over the entire plane of the floor, the screed must have the same thickness. That is, it means that the finishing layer will not be levelling in any way. Level the base must be rough screed for a warm floor. Otherwise it can lead to uneven heating of the entire surface. As a consequence, the heat output will decrease. For this reason, if there are irregularities, differences, potholes or other irregularities, they must be leveled out.

As for the thickness, it should not be too thin. The essence of the screed is that it accumulates heat, and then gives it back to the room. If the layer will be thin, the accumulation of thermal energy will not be. over, a thin layer can provoke the appearance of cracks. At the same time it is not allowed and a great thickness. Otherwise, the heat cannot be fully vented out into the room.

So, if you have a water heated floor, the optimum thickness of up to 70 mm. At the same time above the pipes is about 35 mm, up to a maximum of 50 mm. If you put electric heating, then here the screed on the floor heating will have a thickness of up to 30 mm, and for the film system up to 15 mm.

Underfloor heating into the screed or directly into the tile?

The eternal question of choosing an electric floor in the screed or directly under the tile. This article will try to compare these types of floor heating.

Underfloor heating in the screed

Electric floor heating in (under) the screed is mounted when:

  • repairs at the stage of rough work
  • It is possible to raise the floor level from 3 cm (without thermal insulation) to 7 cm (with EPPS)
  • The speed of heating is not the main thing
  • The floor heating is the main source of heat.

In a warm floor under the screed heating cables are used with a linear power of 15-20 W/m and a thickness of 4 to 7 mm, depending on the manufacturer.

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Advantages and disadvantages of cable systems, mounted in the screed

  • the possibility of purchasing inexpensive cable (as compared to thin cable or heating mats);
  • uniform heating of the floor surface (with a correctly calculated laying step)
  • reliability and fire safety;
  • High thermal efficiency (with properly calculated capacity of the floor heating per m2 and the use of thermal insulation).
  • any geometry of installation of underfloor heating
  • universality of use (under any type of coating, any power per m2)

Under-tile floor heating

If there is no possibility to raise the floor level or if you plan to heat the tiles to a comfortable temperature, then there are 2 options for underfloor heating: a heating mat or a thin heating cable.

The heating mat is a thin cable laid on a fiberglass mesh with a given pitch. Because of its thickness 3.5 to 4 mm for it does not need to raise the floor level and is laid in a layer of tile adhesive directly under the tile. Standard width of the mat is 50 cm. Its basic advantages: The mat is a prefabricated structure and does not require any special skills for installation. (no need to dowel the installation tape to the screed, no need to play with the cable spacing) The mesh on the mat additionally reinforces the tile adhesive. Speed of heating. After turning on the floor heating becomes warm in 20-30 minutes.

Thin heating cable is the same as the screed heating cable, but with less power per m.п. and a diameter of 3.5 4 mm.

Advantages and disadvantages of under-tile cable systems

  • Installed on a concrete base or on top of old ceramic tiles
  • No need for screed, raises the floor level to cm
  • the heating process is faster
  • ease of installation (in the case of heating mats)
  • there is no need to drill screed for mounting tape, with the possibility of damaging the water or heating pipes running along the floor (in the case of heating mats)
  • expensive than a heating cable in the screed
  • A higher probability of damaging the warm during the installation of both the warm floor itself and ceramic tile


If it is possible to raise the level of screed and perform a full thermal insulation, then unequivocally. a thick heating cable. In the case of cosmetic repairs with the replacement of floor coverings, thinner, but more expensive solutions. heating mats or a thin heating cable will do.

Technology of pouring screed for a warm electric floor

Screed for electric underfloor heating is made without regulatory or normative documents. But, nevertheless, there are certain rules associated with the work.

Master, performing the installation, have to take into account the following:

  • The thickness of the screed under and over the heating cable.
  • Choosing the method of screed installation.
  • Nuances associated with the preparation of mortar and the process of pouring.

Correctly made screed for a warm electric floor does not crack, provides uniform distribution of heat throughout the room, keeps durability for a long period of operation.



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