What Thickness Of Screed To Choose For An Effective Underfloor Heating

2023 Author: Philip Bishop | [email protected]. Last modified: 2023-08-25 07:54

• Screed purpose
• Recommendations
• Rough base
• Laying underfloor heating components
• Screed device

According to the technology of underfloor heating, it is most often necessary to pour concrete mortar over heating elements. This is necessary not only to create a level surface for the decking, but also to protect all components. In this case, the thickness of the fill layer will also differ in different situations. Even the manufacturers themselves, in their instructions for installing a screed under an underfloor heating electric, bypass this issue. It is with the thickness that you should decide in the process of laying the components.

Screed purpose

For an ordinary screed, the following functions are characteristic that it performs:

• Protection from external mechanical effects of heating elements and other components of the warm floor.

• Creation of a strictly horizontal surface, necessary for high-quality installation of the selected flooring option.

  

• Uniform heat transfer from the heating elements to the subfloor.
• Distribution of the load on the base from pieces of furniture and household appliances.
• "Mediator" in the transfer of heat from heating elements to the air inside the room.

But it must not only fulfill the tasks assigned to it, but also meet certain requirements, among which are the duration of the operating period, which depends on the quality of the filling and preparation of the solution, as well as the ability to withstand constant temperature drops. With all this, it should not adversely affect heating cables or other elements of a warm electric floor in any way.

All recommendations from manufacturers for pouring the screed should be followed at each stage, not forgetting about the optimal thickness of the underfloor heating screed. During the installation of a warm screed, one should take into account the nuance that such a filling will be more susceptible to thermal expansion. Therefore, it will be necessary to create all the conditions for the ability to withstand all obstacles.

Recommendations

During the work on pouring the mortar for the screed of a warm electric floor, you should adhere to certain recommendations that will allow you not only to qualitatively lay the warm floor under the screed, but also to choose the minimum thickness of the screed.

Much will depend on the power of the heating elements of the heating system in the room. The larger it will be, the thicker you will have to create a fill layer with a solution:

• 80-120 W / m ² - the screed layer will be up to 20 mm.
• 100-140 W / m ² - 30-50 mm.

• 160-200 W / m ² - 60-100 mm.

  

When an electric underfloor heating is performed, the thickness of the screed must be observed depending on the specific conditions of execution and the parameters of the room.

But at the same time, attention is drawn to the fact that the time during which the base of the floor will be completely warmed up will also depend on the thickness of the filling layer. So it is not always very beneficial to create a thick layer from the prepared mortar. In this case, a large amount of electricity will be spent on heating the room.

Before pouring the electric underfloor heating, check the correct installation of the heating elements, as well as the wiring and connection of all components several times. Subsequently, to eliminate the malfunction, you will have to dismantle the screed. All wiring and electrical appliances must be insulated. This also applies to the temperature sensor placed in the corrugated pipe.

If you position the thermal sensor correctly, then if it fails, you will not have to break the tie to remove it. It will simply be removed from the corrugated pipe and replaced with a similar one. It should be noted that the thermostat cannot be installed in a room where there is a constantly high level of humidity.

It is also possible to fill the cable floor with glue. But this is provided only if tiles or porcelain stoneware are used as flooring.

Rough base

Before distributing the heating elements according to a previously prepared scheme, you should check and prepare the base for the warm floor.

It does not always meet all the requirements, it has defects in the form of potholes, height differences throughout the room. This should be dealt with in order not to encounter the weak efficiency of heating the warm floor.

After removing the old flooring and dismantling the concrete base, you can start leveling with a rough screed. For this, a classic sand-cement mortar is used. You can proceed to further activities after it has completely dried and set. Otherwise, you can forget about high quality. The thickness of the screed above the electric underfloor heating is usually up to 50 mm.

The most important thing is to hide all the unevenness of the base and prepare the surface for laying underfloor heating elements.

Further, all unnecessary debris is removed from the surface and, if possible, dust. Here, a construction vacuum cleaner can help to cope with the task. A layer of thermal insulation is laid on top of the rough screed and the subsequent distribution of the underfloor heating cable or heating mat. In some cases, a do-it-yourself floor screed under a warm floor is also arranged over an infrared heated floor. However, at the same time, its efficiency decreases slightly during operation.

Laying underfloor heating components

For the underfloor heating system to function fully, the attachment points for the main sensors and components should be determined before pouring the concrete screed. The thermostat is installed on the wall surface and, if possible, close to the existing outlet. The distance from the floor should be at least 30 cm, since the temperature from the base will somewhat distort the transmitted information.

The temperature sensor is placed in the base of the floor, on which the prepared solution will be poured later. It is worth noting here the moment that with direct contact of the solution, it may fail. To avoid this, the temperature sensor is placed in a corrugated pipe that leads from the thermostat on the wall. All open areas of the corrugation are sealed with a sealant so that the solution does not get into them during pouring. It will not be superfluous to additionally install a special plug at the end of the tube at the base.

The heating elements are laid on the basis of the drawn diagram, where the step of their laying will also be displayed. You should not deviate from the drawing, since all the little things are pre-calculated on it. After finishing work with the components of the underfloor heating, they must be checked for operability by connecting to the mains. The resistance of the cable is measured, which must correspond to the data specified in the passport for it. If the result is positive, you can proceed to directly pouring concrete.

Screed device

The best version of the screed is the use of special ready-made dry mixes for warm floors. They contain all the necessary components, including a plasticizer.

This significantly increases the quality of the finished solution. It should be distributed carefully so as not to damage the heating cable of the warm electric floor. In addition, the mixture must be evenly distributed over the entire surface.

When pouring the mortar, no matter how much the screed should be above the warm floor, air pockets must not be allowed to form. This will help reduce heat transfer from the heating elements to the base.

As mentioned earlier, the optimal screed thickness for a warm floor should be between 30 and 50 mm. There may be times when the minimum screed thickness for electric floor heating is reduced. But then you will have to add appropriate additives (plasticizer) to the solution.

Until the concrete screed is dry, the floor heating must not be started. Otherwise, the solution will not be able to gain the necessary strength and set. After a period of 28 days, you can start trimming the protruding elements of the damper tape and thermal insulation, as well as turn on the warm floors after the screed. The warm floor after the screed is covered with the selected flooring option.

There may be cases when the area of the room is more than 20 m ² or one of the walls in the room is more than 5 meters long. In this case, it is necessary not only to create different circuits from the heating elements, but also to fill the screed in two stages. Expansion joints are necessarily created between the contours of the underfloor heating, so that the integrity of not only the concrete screed during the operation of the heating system, but also the floor covering is preserved.

All these subtleties allow you to get an answer to the question of how to properly make a screed under a warm floor. There are no particular difficulties if you strictly follow the sequence of actions and recommendations from manufacturers. After laying the flooring, the air in the room will be warmed up to the required level.

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