Insulation of walls of a brick house for plastering

Recommendation points

• Insulation: polymer or mineral
• How to calculate the thickness of the insulation
• Adhesive and mechanical fastening
• Adjacent to the plinth and cornice
• Sealing joints and preparing for plastering

In our instructions, we have described for you a typical technology for insulating brick walls for finishing the facade using “wet” technology. You will learn about the advantages of two main types of insulation, their use in different climatic conditions and the process of installing thermal protection of a building.

Insulation: polymer or mineral

There has long been a debate about the best insulation material. The undisputed leaders at the moment are foamed polyisocyanurate (PIR) and polyurethane (PUR). Both of these materials came to construction from the military and space technology industry, in the 21st century they have become ubiquitous. Due to one of the lowest thermal conductivity and low weight, moisture resistance, incombustibility and moderate environmental friendliness, such insulation remains, perhaps, the most effective, safe and durable.

Extruded polystyrene foam (XPS) is a cheaper replacement for higher grade polymer insulation. The only drawback is that even without spreading fire, these materials are extremely toxic when heated. Therefore, it can be quite difficult to fit polystyrene insulation into the framework of fire safety. However, the XPS is just as wet-resistant, lightweight and durable, making it very popular..

Mineral wool, with proper installation, may not be inferior in the efficiency of insulation to polymer plates, but it has a number of disadvantages. A careful calculation of the displacement of the condensation point at different temperatures is required, since the appearance of moisture in mineral insulation increases its thermal conductivity tenfold. A peculiar problem is the inability of loose cotton wool to form a plane for applying “wet” finishing materials, therefore, only suitable for wall insulation under plaster are:

• mineral slabs with a density of about 120-150 kg / m³, but with them the mass of the building increases significantly;
• multi-layer (heterogeneous) slabs with more rigid outer layers, due to which reliable fastening of both the insulation itself and the finishing to it is ensured.

How to calculate the thickness of the insulation

The required thickness of the insulation belt is determined by its resistance to heat transfer. According to the standards for thermal protection of buildings according to SP 23-02-2003, the optimal resistance for the walls of residential buildings is taken to be from 2.1 to 5.6 m²* K / W, it grows with the duration of the heating season and the temperature difference. In practice, this value turns out to be not high enough, with such an efficiency of insulation, heat loss of buildings is in the range of 150-200 kW * h / year from each square meter.

A high-quality insulated residential building can be called a building where about 70-100 kW * h / m is required to replenish heat losses² in year. With such initial data, it is possible to reverse the calculation procedure, which is performed separately for each type of enclosing structures: walls, floor, glazing, ceilings.

1. It is necessary to determine the temperature regime of operation, taking as a starting point the calculated internal temperature and the temperature of the outside air in the coldest five days.
2. The thermal conductivity of the supporting layer of the walls should be determined. For a brick, for example, this is 0.5-0.7 W / m * K, that is, with a total wall area of ​​100 m² 40 cm thick with a temperature difference of 35 ° C, the total heat loss will be 4.4-6.2 kW hourly or about 150 kW / m² for the entire heating period.
3. The resulting value is significantly higher than the norm and the thickness of the walls must be increased. In this case, a value is used that is the opposite of thermal conductivity – resistance to heat transfer. It is expressed by the relationship R = p / k, where p is the thickness of the wall layer (0.4 m), and k is the thermal conductivity coefficient (0.5–0.7 W / m * K).

1 – external finishing of the facade; 2 – insulation; 3 – adhesive layer; 4 – brick wall array; 5 – a layer of plaster; 6 – a layer of interior decoration

The total resistance of the wall is equal to the sum of the resistances of its layers (bearing and insulating), so it is possible, in the reverse calculation, to calculate the required thickness of the insulation, knowing its thermal conductivity coefficient. An alternative to manual calculation can be called all kinds of calculators, of which the most reliable data are provided by the programs provided on the website of the manufacturer of the material used for insulation.

Adhesive and mechanical fastening

There are two ways to fix the insulation to the load-bearing layer of the wall. Their presence does not imply freedom of choice: both glue and disc dowels should be used, because they perform different functions. The only exception is walls that cannot be glued to, such as wood.

The glue performs the main fastening function, it is applied to both surfaces either with a comb or with dotted strokes in the center and in a continuous strip along the contour of the slab. A continuous layer of glue can significantly limit the vapor permeability of the enclosing structure and provoke the formation of condensation in the glue joint, its delamination and loss of fixing strength. For this purpose, disc dowels are used – this is a kind of safety belt that makes up for the lack of fastening strength in case of non-continuous application of glue.

For different heaters, the fastening sequence is different. Polymer plates are fixed with dowels immediately so that the stiffness of the insulation does not provoke shifts and flaking. In this case, the dowels provide temporary fixation of the boards until the glue dries. The latter can be applied in a continuous layer, because the intrinsic vapor permeability of the plates is already extremely low.

U-shaped hangers can serve as an alternative to plastic dowels. They are fixed on the wall, the insulation is stitched with the wings of the suspension, which are then bent in different directions.

When installing mineral wool, fastening with disc dowels is carried out not earlier than 2-3 days after gluing the boards. This is due to the phenomena of shrinkage of the glue and the plates themselves, which absorb moisture from it to a limited extent. Fastening with dowels to replenish strength is carried out at least at 4 points around the perimeter and 2-3 in the center of the slab.

Adjacent to the plinth and cornice

Sometimes the basement or cornice part of the wall protrudes above the main plane, while the installation of any insulation is performed in a continuous vertical row with a constant thickness. In such cases, it is necessary to provide a technological abutment to the protrusions, which excludes the ingress of rainwater into the thermal protection, and also guarantees a slightly more intensive ventilation of the damp lower zone.

Even before fixing the insulation, support perforated trays are installed. They are fastened to the wall along the base / plinth line, spaced with mounting wedges to obtain an even starting line. If there are significant differences in the plane on the wall – more than 5 mm / m for polymer and more than 10 mm / m for mineral insulation – they are leveled with plaster along a plumb line, taking the tray as the generatrix of the vertical plane.

If it is necessary to ventilate the under-roof space, the wall insulation cannot be raised close to the crate. Overhangs need to be knocked off with a wind board with ventilation lamellas, and then spread the plates all the way, setting them up. It is not necessary to observe the angles of inclination of the overhangs, the end of the slab is cut only at right angles.

The adjoining to the openings is performed with a small protrusion of the insulation inside. If it is necessary to install wider ebbs, the old ones must be removed immediately and a slab overlap of 20-30 mm should be made under them. This is due to the fact that when decorating these areas, the excess insulation is accurately cut off, and the formed ends are used as a basis for applying plaster of the slopes.

Sealing joints and preparing for plastering

Installation of insulation boards is carried out in a horizontal position with an interval of at least a third of the length, which ensures the overall strength of the belt. Protection against blowing out and the formation of cold air bridges is performed by tight sealing of the joints between the plates.

The seams of polymer boards are filled with polyurethane foam to the full depth, the squeezed out residues are cut off with a scraper. The joints between mineral boards are usually filled with an adhesive mixture. When using warm plaster (TS) as the main coating, it is better to fill the joints with it as a less heat-conducting material.

Regardless of the final decorative finish and the plaster used, the external insulation must be covered with a preparatory plaster coat. In the case of mineral materials, the coating must support gas exchange while remaining hydrophobic to moisture from the outside. If the insulation is made of polymer plates, then the main task of the preparatory layer is to fix the reinforcement made with glass fabric mesh, as well as to improve adhesion under the main plaster.

The exception here, again, is TS: since the slabs form a fairly flat plane, it is possible to apply a uniform outer layer without increasing the cost of leveling. To reduce water absorption, the surface of mineral slabs can be impregnated with a bonding primer.