How much to fill the screed on the warm floor

Cement and sand mixture

How to properly pour the floor under a warm floor with a water loop? The most common type of screed. from cement and sand. It is easy to work with, sand particles act as an excellent plasticizer.

Typically, cement-sand mortars of grade 150 are used to perform concrete work in living rooms. For installation of the water floor it is recommended to take M200. With increased loads on the floors, you can and a higher grade:

Factory mixes, which will be delivered to the place of repair, are purchased at mortar units. In stores they are packed in bags. You can also make the mixture yourself. This is a more time-consuming way, but economical. You need to keep the dosage of the components and find river sand with a coarse fraction.

much, fill, screed, warm

Cement-sandy mixtures for damp rooms (bathrooms, swimming pools) are made with cement M400. Cement M500 quickly gain strength and is suitable for rooms with dry floors. The recommended thickness of the screed warm floors about 40 mm. Laying a water heated floor in the screed in this case will be performed without difficulty.

How to properly pour a water heated floor, so that it serves for a long time? It should be resistant not only to mechanical but also thermal effects. It is recommended to add polypropylene fiber in the mortars: 900 grams per 1 cubic meter. The cost of this additive is not high, but it will raise the level of screed strength and prevent the appearance of small cracks. Be aware that the fiberglass additive does not replace the reinforcing mesh.

What is the minimum thickness of the screed for water underfloor heating. rules and regulations

In the arrangement of a warm waterborne floor over heating elements is poured screed, which is used as the basis for the final floor covering. For private home masters who dare to mount a system of underfloor heating themselves, the question of the thickness of the screed is relevant. What should be the height of the screed of a warm floor so that the heating elements are not damaged by the loads during operation, and the heating was as effective as possible. To answer this question, it is necessary to study the features of the system and the properties of the materials from which the finished floor will be made. In addition, in the SNIP there are certain recommendations related to this issue.

Screed for a warm water floor: installation rules

It is impossible to make a quality warm water floor without proper installation of the screed. In addition, you will need to buy a modern floor covering, materials for creating a pipeline and components of the mortar for pouring. Failure to follow the technology of the work leads to the fact that the screed for a warm water floor is defective and all efforts aimed at heating the room are in vain.

If professionals from a construction company are hired to install the system, it does not hurt for the homeowner to know the basic rules of its creation to make sure the service is done properly. After reading the relevant information, property owners have the opportunity to exercise direct control over the construction work and, if necessary, to point out flaws, demanding to eliminate errors.

What is made of screed under the warm floor?

To properly and effectively make a screed under a warm floor, you need to know what to make it from. In the classic version it would. Cement-sandy, but that does not mean that only cement and sand are needed to make it. Very often in the composition of the screed for underfloor heating add special plasticizers, to save cement add expanded clay or gravel. Then the screed turns out to be concrete, and the cement in its composition may be different, taking into account the future floor covering. There are no strict approved standards for the composition of the screed. However, it is generally accepted that the proportions of the components of an ordinary screed for a warm floor are as follows: sand 3 parts and cement 1 part, and water is added to obtain a solution the consistency of liquid sour cream. PVA glue is mainly used as a plasticizer, it is used at the rate of 1 kg of glue per 1 bag of cement.

There are other proportions for screed, depending on the future use of the floors. The ratio of fractions between the components may be as follows to one fraction of cement added sand five shares and water (0.7 shares), in that case, if after hardening on the solution for floor screed will be laid parquet, laminate or tile. If used as a floor covering soft materials (carpet, linoleum), the ratio may be different: cement 1 part, sand 4 parts, water 0.7 parts. When crushed stone is added to the mixture for screeding a warm floor, then the ratio between the components will be as follows: cement 1 part, sand 3 parts and 5 parts of crushed stone. To prepare such a mixture will require water, usually up to half the weight of the cement. The arrangement of screed floor heating can be made much easier and faster if you use special ready-made mixes. How to properly use ready-to-use mixtures is described in the instructions that come with them.

Thermal conductivity of semi-dry machine screed for water underfloor heating

Reprinting of articles and parts thereof is prohibited. We want to reserve the right to exclusively host this material on our website. Here we share the knowledge and experience gained by our team over the years in the design and installation of engineering systems.

Introduction above

  • Is a semi-dry screed suitable for water underfloor heating?
  • What is the exact value of thermal conductivity of semi-dry machine screed floor?
  • How much it differs from the thermal conductivity of a traditional screed?
  • Whether it will have a negative impact on the heating of the underfloor heating?
  • Wouldn’t this increase the cost of operating the building? and t.п.

We will try to answer these and some other questions in this article.

Actual data on the thermal conductivity of traditional concrete, cement-sand, and semi-dry screeds for floors above

  • The thermal conductivity coefficient of concrete on gravel or crushed natural stone is about ;
  • The thermal conductivity of cement-sand mortar with a density of about.
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Harris Floor Screeding Limited. Installing a traditional fibre reinforced screed

Of course, you must understand that these figures depend a lot on the quality of preparation and laying of the mixture, its humidity, etc.п., but they give us a pretty good guideline.

As for the thermal conductivity of semi-dry mortar, there is no such data in this SNB, for it is a military secret no one knows and no one needs. However, there is an interesting document: Study of the thermal conductivity of semi-dry unbound cement-sand screed. Technical report. This study was performed as far as the Institute and has many signatures, and even a seal with a cabbage eagle. According to the results of this study, the thermal conductivity coefficient) of the samples of semi-dry screed with a density of about

  • The thermal conductivity (coefficient) of the concrete screed is
  • The thermal conductivity of a cement-sand screed is
  • The thermal conductivity of a semi-dry screed is

What do these numbers tell us? up

A somewhat well-read and suspicious person will immediately say, “HERE! This is where we get screwed! What a waste and loss”. And will be right only in the fact that indeed, the thermal conductivity of semi-dry machine floor screed is 2 times less than the thermal conductivity of conventional screed and as much as 4 times less than concrete screed. But what does it mean in practice? And this is a little more complicated than just dividing 8 or even 16 by 4.

This example shows that the heat transfer coefficient of a piece of masonry made of ceramic hollow bricks is

The material’s heat transfer coefficient is numerically equal to the heat flux in watts which, if passed through a one-meter-thick layer of a given material, causes the temperature to drop by one degree Kelvin over that distance. Т.е., The higher the thermal conductivity of the material, the higher the heat flux that a layer of this material can let through at a given temperature difference at its boundaries.

So let’s return to the screed case. The smaller the thermal conductivity coefficient of the screed, the greater the temperature drop needed between the heating pipes (the average temperature in the supply and return of a warm floor) and the floor surface temperature to transfer the same amount of thermal energy into a given room. A higher temperature difference in this case does not automatically mean more energy, power or money is required for the houses. Confusing temperature and energy = confusing blue and wet.

How much to increase the water temperature in the underfloor heating pipes when using different types of screeds? above

Let’s take a concrete, typical example from life and calculate all the values we are interested in. Let’s assume that we have a room with an air temperature in and specific heat loss of. For these parameters, the surface temperature of the screed will be 26C (remember the cherished figure of 11 W / C). Let’s make three different variants of the screed of the same thickness over the floor heating pipes, but made of different materials: concrete, cement-sand mortar (CPR) and semi-dry mortar (DMA). The thickness of insulation under the warm floor heating pipes is taken the same for all three variants The air temperature in the room on the floor below is also the same for all variants and is 10. A variant with a 50 mm screed over the underfloor heating pipes would roughly correspond to a situation where the floor is finished with ceramic tiles laid on glue over a screed of a total thickness of

Given the required value of heat flow upwards, the thickness of materials and their thermal conductivity coefficients, let’s calculate the temperature drop on the wall of the underfloor heating pipe and the thickness of the screed during the heat flow through them. The temperature drop will be: 3.3K for a concrete screed, 5.0K for a screed made of CPR and 8.0K for a semi-dry machine screed (for all three cases, the temperature drop on the wall of the floor heating pipe itself is about 1.5K). Different temperature drops in the thickness of the screed leads to the fact that in order to maintain a given heat flow from the underfloor heating pipes, it is necessary to change the supply temperature to the underfloor heating accordingly. Thus, for a concrete screed, the supply temperature will be around 35C (5C higher than the average temperature of the heat transfer medium), for a screed made of cementitious reinforced concrete screed 36C, and for a semi-dry machine screed 39C. Т.е. To compensate for the screed’s high heat transfer resistance, the supply temperature to the underfloor heating needs to be raised by

What this means? upwards

  • The room has a high specific heat loss of the order of and above.
  • A large laying spacing of floor heating pipes of the order and more is used.
  • Final floor coverings with high heat transfer resistance (laminate on subfloor, thick carpeting, etc.).п.), and the thickness of the floor screed is higher than the usual value of 40 mm above the pipe.

Let’s calculate for example the temperature drop for this case. The plaster over the floor heating pipe has a thickness (the total thickness of heat flow upwards the air temperature in the room is 20C, the floor surface temperature is 27C, the final floor coating is laminate on the substrate

As long as the supply temperature to the floor heating does not exceed any particular problem for heating systems based on gas wall and floor boilers, solid fuel and electric boilers does not arise. Even when using gas condensing boilers it is quite difficult to assess the real reduction of boiler efficiency from the supply temperature of 50C compared to 40C (because in any case the return temperature of underfloor heating will be about 45C, which is below the dew point of natural gas combustion products).

According to some sources (cf. Fig. below), the drop in efficiency of condensing boiler at increasing the return temperature from 35C to 40C (supply respectively 45C and 50C) will be about It should be taken into account, however, that the maximum calculated temperature in the heating supply will be needed only for a few days during the entire heating season.

Increasing the supply temperature to the underfloor heating leads to increased heat loss downward through the building structures of the floors and floors. But in the case of a warm floor above the operable rooms of the floor below, these heat losses will not be useless. In our first calculation above, you can see that a 4K increase in supply temperature resulted in an increase in specific heat loss downward from for concrete to for semi-dry screed flooring. Using a semi-dry machine screed for a square foot water heated floor will result in an increase in downward heat loss for the entire house by which is insignificant.

Increasing the required supply temperature to the underfloor heating can present a certain inconvenience when using home heating from solid fuel boilers with buffer tanks. In this case, the operating temperature range between full charging and discharging of the heat accumulator will be reduced by increasing the supply temperature to the floor heating. For example, if you need to increase the supply temperature to the floor heating from 45C to 50C, the useful capacity of the heat accumulator with a maximum loading temperature of 85C will be reduced by 15%. This is not much, but requires consideration when planning the operation of heating systems from solid fuel boilers.

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Conclusions above

  • Buildings with high heat losses and thick floor screeds which will however have high thermal transmittance finishes such as laminate, carpet, plank flooring.
  • Poor floor insulation, especially over ventilated basements, driveways, etc.п. (But why build such houses at all?)
  • Underfloor heating from a heat pump.
  • House heating by underfloor heating from a solid fuel boiler with a buffer tank.
  • Customer-builder.

If you need to carry out the design and installation of engineering systems for your home in Minsk and Minsk region; you want to get advice and perform installation of heating, water supply, sewerage, ventilation, built-in vacuum cleaner, to make the necessary calculations and select equipment, or you have encountered difficulties in implementing your ideas, we will be happy to help you.

Casting the screed, taking into account the type of underfloor heating

Many people who have decided to independently install electric floors in their home, ask a reasonable question about how the screed for a warm floor is performed. In fact, this process is not too complicated and does not require a long time. But it should be carried out taking into account the archival factor. the type of heat floors, which are planned to install.


If it was decided to organize water floors with heating by yourself, you will need to understand the basic rules of pouring screed for such a system. Screed under the underfloor heating will raise the entire heating system up to a certain level, but if you compare this option with other alternatives, it becomes clear that this is quite an economical option. The construction turns out to be layered. It is made of the following materials:

  • waterproofing;
  • insulation material;
  • a layer of foil;
  • heating system pipes;
  • Reinforced screed;
  • finished floor.

To prevent pipes from floating, they should be fixed by attaching to the reinforcing mesh or insulation. Pipes can be laid in different ways. Pipes can be laid in these ways:

Pour the prepared concrete mortar over the pipes, starting from the far wall, and towards the door. The room in this case should be divided into zones with reference to the beams. Poured concrete on pipes should be carefully leveled with a rule to avoid skewing the thickness of the base. When using semi-dry mixes, already in 6-7 hours after the organization of the screed, it is worth to grind.


Above described how to fill a water heated floor yourself, without paying the services of a hired team of builders. Now let us dwell on the details of how to pour an electric floor heating. It is poured in this case somewhat differently.

First, let’s note that electric underfloor heating is diverse in its structure, which determines the specifics of installation work:

Foam floors are allowed to lay over a layer of concrete, while the other two options are poured into the screed.

In general, such floors are organized in the same way as the water floors, but taking into account the fact that the electric cables or mats are mounted directly on the reinforcement grid, which is suspended between the joists. Cables must not touch the thermal insulation material, and a plasticizer must be added to the screed mortar for electric floors. After fixing the cables or mats on the reinforcing mesh, mortar is poured on the structure and wait 4 weeks for it to finally harden. The dried floor needs to be sanded and then covered with a finishing material.

About the thickness of the screed in general terms

There is no universal answer to the question about the optimal thickness of the screed layer. This point depends largely on the following indicators:

  • The type of ground, in the case of installation of water heated floor in a private home when pouring a general concrete layer;
  • peculiarities of the room configuration;
  • the purpose of the room to be built up.

The above points are basic. In addition to these there are a number of other nuances, for example, the brand of cement or self-leveling mixture, the characteristics of the reinforcement and reinforcing mesh, etc.д.

The type and thickness of the screed depends on many factors

Conventionally, we can distinguish 3 main varieties of screed water heated floor. The information is given in the table.

Table. Types of screed for a water heat-insulated floor

Minimum thickness On the order of 2 cm It is created with readymade self-levelling mixtures. Reinforcement is not carried out.
Average thickness About 7 cm The reinforcing grid or reinforcing thin rods are used.
The maximum thickness On the order of 15-17 cm Monolithic system with reinforcement. It is used in case of arrangement of integral support system which is a part of house foundation and floor at the same time.

On the thickness of the layer also affect the characteristics of the materials that make up the mixture. For example, the thickness of the screed using crushed stone cannot meet the above minimums, i.e.к. The fraction of the elements makes this impossible.

At the same time there is a wide range of ready self-leveling mixes, that do not require too thick a layer to be poured. Such compositions are used for leveling the surface directly before laying the finishing material.

Self-leveling pouring floor is perfectly compatible with pipes of water underfloor heating

In general, the layer must be of such a thickness that the heating elements are completely covered by the casting. In view of the fact that the maximum diameter of the pipes from which the system of warm flooring is collected, does not exceed 2.5 cm, we can say that the screed thickness of the order of 5-7 cm in most cases will be enough.

However, along with the above information, it should be borne in mind that when using the system in question, heat is released, under the influence of which the concrete part of the “pie”, and with it, and the final coating will expand. It is necessary to make the screed of such a thickness that the final coating material was subjected to thermal deformations to the least extent, but, at the same time, kept the optimal thermal conductivity.

It is necessary to make the screed of such a thickness that the material of the finish coating was subjected to temperature deformations to the least extent, but, at the same time, retained the optimal thermal conductivity

Too thick screed on top of a water heated floor experts do not recommend pouring. It is meant that over the pipes should not be more than 4-5 cm of concrete mixture. It is important to understand: the thicker the filling will be, the more energy will be consumed by the system and the more difficult it will be for the user to control the intensity of heating.

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Execution of working operations

The exact sequence of steps depends on what screed under a particular water heated floor is chosen as a result. Nevertheless, the following tips from experts will be useful when reproducing with their own hands specific technological processes.

Before pouring a rough screed water heated floor must install power cables, other engineering lines. The walls and ceiling are leveled with plaster mortar. If you perform the work in the reverse order you will have to wait for the screed to cure. Further it will have to be cleaned from new dirt.

When forming these building structures, control the perpendicularity of the corners to ensure tightness of the joints with the thermal insulation slabs. On a well-created surface are not allowed to have differences of more than 5-6 mm in height for one circuit. This will prevent the formation of “plugs” of air.

If you choose polystyrene foam boards of sufficient density, no special precautions are needed. These products will withstand the weight of an adult without deformation and damage. However it is necessary to check cleanliness of footwear, to remove from a sole and from a surface potentially dangerous pollution. It is better to install gangways of boards for moving. Do not forget that when pouring construction mixtures will have to move heavy weights.

With a large area of screed water heated floor requires the installation of expansion joints for every 20-25 square meters. area. They will prevent the appearance of cracks when the temperature rises / falls. The tape from the polymer foam (polyethylene) 100-130 mm wide and 7 to 12 mm thick will do. These elements are installed only in the main screed.

At this stage it will be useful to plaster the walls (at least to a level of 40 cm from the floor). Some types of specialized damping tapes are covered with an adhesive layer on one side. They attach quickly and firmly to even surfaces.

At the stage of preparing drawings screed water floor heating must accurately establish the intersection of pipes expansion joints. They are placed only at the intersection of supply and return lines. On the open sections of the pipeline (from the screed to the collector and back) set the heater.

The green line indicates the correct location of the expansion joint

For creation of a building mix concrete grade from 150 to 300 is suitable. Such a range is specified in reference books, in order to provide for different purposes of surfaces. Stronger screeds (M300) are needed at commercial facilities, warehouses, production halls. In residential and office premises concrete is created from one part of cement M150/200 and three parts of sand.

Strengthen the composition of the screed water warm floor with the help of a small granite crumb. Since it is supposed to function in a mode with changing temperatures, it is necessary to increase the plasticity of the screed. Experiment with PVA and other adhesives series is not necessary. Suitable “free recipes” can be found on the Internet, but their actual usefulness is difficult to confirm.

To screed for a water-heated floor to turn out reliable, it is necessary to apply specialized additives. They are covered by official warranties. In the detailed descriptions of the manufacturers are instructions for the proper use of.

For the filling of the main screed water underfloor heating apply the following algorithm:

  • Work performed at a temperature in the room at least 0 ° C.
  • First you check the tightness of the system, fix the detected leaks. To do this, the pressure is raised (up to 4 atm) for one day.) for one day. Next. set the nominal pressure (from 1.5 to 2, 5 atm).). Control the values with a manometer.
  • On the walls are marked, indicating the level of the surface of the future layer. To create an even screed, in the room create mounds (“beacons”) of the required height.
  • To move the long rule, support rails are installed. On them the device is moved, removing surface irregularities.
  • Pouring of mortar begins from the far area, shifting to the entrance. Remove gas bubbles from it with a rammer. A simple method, repeated strokes with a metal rake, requires a lot of work. A specialized floor vibrator for construction mixtures can help you perform the necessary processing faster.
  • During the operation check the height of the screed on the marks applied to the walls.
  • The amount of mortar is created in such a way that the portion of the mixture can be laid in a few hours, but no more. It is necessary to calculate the technology so that one entire room was filled in a day. To accelerate the processes, stirrers or other means of mechanization with electric drives should be used. You do not need to buy this equipment. It can be rented.
  • No later than 3 days later the guides (beacons) are removed. Deepening of the screed water heated floor is leveled with mortar.
  • To screed hardening is not accompanied by the formation of defects, it is moistened 2-3 times a day.
  • After three days on the surface roll out the film to prevent too rapid evaporation of moisture.
  • In normal temperature conditions the screed will be ready for installation of the final flooring in 25-30 days. During this period, do not heat the thermal fluid more than 28°C.

Parquet block and some other fine wood products are installed when the relative humidity of the screed is below 55-65%. If this level is not achieved, the drying period is extended.

Thermal insulation

To prevent heat loss through the floor is used thermal insulation. When selecting it take into account heat-protective properties, which depends on the overall thickness of the screed. On the first floor as thermal insulation plates are used 5 cm thick, if there are apartments with heating below, you can use insulating layers no thicker than 2-3 cm.

The thermal insulator is taken with a metallized coating. Aluminum foil does not withstand a long contact with the screed and is destroyed. It is necessary to apply metallized coatings in the form of spraying with lavsan and t.п.

Laying thermal insulation for underfloor heating

Laying the tiles is done without gaps. The resulting gaps are filled with assembly foam, all joints are glued with adhesive tape.

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