Underfloor heating installation: laying mats and preparing the base for the tiles

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Today we will introduce you to one of the classic floor heating schemes. This option is especially good for apartments: it practically does not require chipping, does not increase the cost compared to water heating, and gives complete freedom in the choice of coverage, including ceramic tiles..

Underfloor heating installation

What preparation does the floor require?

In most cases, underfloor heating systems on electric mats are designed for non-professional installation. The scheme of the device allows some deviations from the generally accepted technology, including laying on an unprepared base. Regardless, it is best to demonstrate a more balanced and consistent approach. This will help improve the efficiency of heating and increase the life of the floor, even with significant traffic loads..

Underfloor heating installation

You should start by planning the floor according to the general horizontal level. It is very important that heating elements and other parts of the system are tightly fixed against each other. It is almost impossible to achieve this without a flat plane as a basis, so you should prepare for two things:

  1. Arrangement of a leveling and reinforcing screed throughout the entire area of ​​the heated room.
  2. Slight loss of height between ceiling and floor due to the required sequence of preparation layers.

Since it is intended to carry out “wet” construction work, the floor should be carefully waterproofed. It is best to use bitumen-based coating mastics for this. A continuous floor covering is not required, it is enough just to process large cracks, joints between slabs and corners around the perimeter of the walls.

Leveling preparation screed

In some cases, the floor may be covered with a screed that is sufficiently flat, but does not meet the strength requirements. In this case, it is better to dismantle at least especially damaged areas. If the situation develops in the opposite way, that is, the coating is strong, but not even enough, the screed is poured in the same way as over the concrete floor, but without additional waterproofing.

Underfloor heating installation

The best solution for preparation is a solution based on DSP grade 300 or 350, and when working in office or industrial premises – not lower than 400. Before leveling the floor, it is imperative to treat it with “Concrete-Contact” for high-quality adhesion.

Underfloor heating installation

When pouring the screed, it is important to adhere to a minimum layer of 10 mm. Thus, at the zero (highest) point of the floor, the screed layer will be 10-15 mm, and throughout the rest of the area – according to the level difference. The preparatory screed does not require reinforcement, but after drying it should be treated twice with a deep penetration primer.

What kind of insulation to use

Most of the installation instructions do not imply a thermal cutoff under the heating mats or simply do not describe its design. Nevertheless, this element is very important, especially in apartments or when installing underfloor heating on the ground. Otherwise, the lion’s share of the energy will go into a more heat-absorbing material – a floor slab or floor, without heating the surface properly.

Using low density materials under the screed may not seem like a good idea. Obviously, in such conditions, the floor will simply squeeze and crack, isn’t it? This is not entirely true: such phenomena only happen when using insulation with a high degree of compressibility, such as foilgoizol (penofol) or low-quality PSB.

Underfloor heating installation

If you use polyurethane foam boards with a thickness of 10 mm or more, then there will be no problems. This material has excellent resistance to deformation during compression, if at the same time it is located between two flat incompressible layers. This is precisely why careful preparation of the lower layer is needed: this is how a load resistance of at least 200 kg / m is achieved.2, the deformation of the insulation is reversible.

It is important that during installation, the insulation boards are securely fixed to the base. To do this, grind tile adhesive over the slabs and on the subfloor and remove the remnants with a comb-type spatula with a tooth height of about 2-3 mm. It is very important to leave a minimum amount of glue, so in the absence of a suitable tool, you can grind a larger spatula with a grinder.

Underfloor heating installation

Ideally, the adhesive stripes on the tiles and the floor are perpendicular during installation. The insulation must be well pressed with your feet and the plates must be tightly fitted to each other.

Electric floor heating system

The main difference between underfloor heating mats is that the heating cable is already fixed on a reinforced substrate. This maintains a constant indicator of energy density – no more than 130 W / m2, and the user does not need to independently calculate the cable pitch. There is also a guarantee that the power will not be too high for such capricious surfaces as tiles or porcelain stoneware, and overheating will not cause the adhesive to peel off..

Underfloor heating installation

Otherwise, the structure of the heating system is similar to a foil or underfloor heating. The length of the cable in one segment is designed for direct connection to a 220 V network, the control is carried out by a cut-in-type thermostat, which is installed by analogy with sockets and switches. The connection of the power cable to the heating cable is carried out with special clamps of increased reliability from the delivery set, which, after crimping, are insulated with a heat-shrinkable tube.

Underfloor heating installation

The layout of the mats is very simple. Usually the route starts from the place where the thermostat is installed and continues along the same wall until it meets an obstacle. It can be either another wall, or a section of the floor on which heating is not needed and even harmful, for example, under permanently installed furniture. Then the mat backing is cut and the rest of the mat is rotated due to the flexibility of the heating wire..

Underfloor heating installation

The principle of stacking is the same as in the well-known snake game. The number and direction of turns during laying is not limited by anything, it is only important not to damage the cable. Also note that the backing outlets around the edges of the mat adjust the distance of the cable from the walls and the pitch for parallel installation. Therefore, the substrate should not have overlaps, if this is not provided for by the markings applied to it..

Large area work

The installation of underfloor heating mats in very spacious rooms looks somewhat different. In the usual case, the load from the heating cord is connected directly to the thermostat, the relay group of which is designed for a current of up to 16 A, which at a voltage of 230 V corresponds to about 3.5 kW of heating power.

In reality, such a load mode will disable the thermostat very quickly, so it is desirable that the current in the load circuit does not exceed 10 A (2.2–2.5 kW). With an energy density of 130 W / m2 the maximum heated area is limited to 20 m2.

Underfloor heating installation

One of the solution options is to divide the room into sections of the maximum permissible load area, adjacent to the walls, and carry out the installation in the usual way. In this case, each heating zone will be equipped with its own thermostat with the possibility of individual adjustment..

If necessary, you can connect several mats in series and control them with one thermostat. This requires switching the load through an intermediate contactor of appropriate capacity and laying the supply line with a more powerful cable. Branches can be made either by partial cutting without breaking the core, or walled up in the floor with an unattended junction box and connect the wires with soldered screw terminals.

Laying and protecting mats

In many installation instructions, the mats are simply rolled out on the floor and are not held in place until the tile is applied. This approach does not exclude the shifting of the heating elements inadvertently and is generally not very convenient. In addition, it is so very difficult to achieve really high-quality adhesion of the top layer of the screed with insulation.

Underfloor heating installation

When the mats are laid out according to the laying pattern, they should be thrown to the side one by one and the insulation under them should be carefully wiped with a thick DSP solution. Excess mortar is removed with a comb trowel, but this time the tooth height is at least 10 mm.

When the area for the underfloor heating segment is covered with a solution, the piece of the heating mat is returned to its place and carefully pressed down with a wide bar, applying it across the turns of the wire. Segment by segment, thus fixation of all mats is carried out over the heated area. Excess mortar is usually removed flush with the heating cable, and the floor remains dry for 24 hours.

Floor preparation technique for tiles

Underfloor heating installation

The tiles can be installed in the usual way, having previously treated the surface with a primer for better adhesion of the layers. However, it is still better to fill in a small layer of accumulating screed, covering the heating elements with a DSP layer of about 25–30 mm. So the floor will become more solid, the inertial overheating will be leveled and the probability of the so-called thermal zebra will be guaranteed, which often happens when laying tiles immediately on top of the mats.

Underfloor heating installation

We recommend that you do not stint and perform the top screed according to all the rules: first, lay out a reinforcing mesh made of fiberglass or polyethylene, and then install linear beacons to comply with the general plane. Since the screed layer is thin enough, it makes sense to use a primer more often for reliable adhesion of the layers to each other..

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