Insulation of the walls of the house from the outside with foam

Recommendation points

• Foams: material classification
• Suitable types of carrier bases
• Surface preparation
• Installation of insulation boards
• Protective plastering
• Facade finishing compounds

Polyfoam is not prohibited for insulating low-rise buildings and therefore it remains a fairly popular material. Active use is facilitated by the low price of foam, its durability and simple installation process, which we will discuss in today’s review..

Foams: material classification

In a broad sense, foam refers to any type of plastic foam. However, in the construction industry, this term is most often referred to as expanded polystyrene made by non-pressing molding – PPP (PSB) or EPS. It is one of the cheapest and easiest to manufacture materials, commonly used as a heat insulator..

Thermal conductivity of PSP is lower than that of most types of mineral wool – about 0.035–0.04 W / m · K. It also surpasses mineral wool in performance properties: it has low compressibility and high compressive strength. Depending on the required range of qualities and the specifics of the application, different brands of expanded polystyrene are used.

The digital index after the PPP abbreviation determines the maximum density of the material. For external insulation of buildings, polystyrene foam of the PPS-16F brand is used. This is a kind of golden mean for the density of the material – it is strong enough to carry additional load and resists heat transfer well.

In addition to the strength properties, PPS can differ in flammability. Regular foam without additives burns very intensely and produces pungent smoke due to the use of natural gas to foaming the polymer. If the letter “C” is indicated at the end of the marking, such a material has self-extinguishing properties due to impurities, fire retardants and replacement of natural gas in the pores with carbon dioxide. Nevertheless, the toxicity of the material during combustion remains very high due to the large doses of styrene released during combustion..

More specific brands have the letter “F” in the marking, so they designate the range of products intended for facade decoration. There are no special differences from ordinary polystyrene, just one of the sides does not have a glossy sintered, but a somewhat rough surface, which facilitates the application of plaster.

Suitable types of carrier bases

Polyfoam is widely used because of its versatility. It is a very lightweight material that does not exert significant stress on the wall to which it is attached. And since most private buildings are low-rise, indirect loads can be neglected..

The main limitation for the installation of foam boards is surface adhesion. In modern construction practice, it is very difficult to find materials for enclosing structures, to which it is difficult or impossible to glue the PPP. For different types of substrates, there is a line of adhesive mixtures that provide reliable fixing.

On the other hand, it is possible to exclude clogging of moisture in the bearing layer of the wall only on condition that the layer of external insulation and decoration will have sufficient vapor permeability. This indicator for polystyrene foam is not zero, unlike EPS, PUR and PIR, but still not high enough for pasting walls made of foam or aerated concrete blocks without an internal vapor barrier. To insulate such buildings, a 100% guarantee of the dew point displacement inside the insulation is needed, which is achievable, as a rule, with a foam layer of the order of 150-200 mm.

Ideal for insulation with foam, like most foam-polymer heaters, buildings made of bricks and concrete, as well as frame structures based on self-supporting insulated wire, are suitable if they need additional thermal insulation. The use of PPS on bases with high porosity is possible if the enclosing layer is formed by a stone cladding while maintaining ventilation gaps. This technology is the subject of a separate conversation, now we will focus on the practical implementation of the so-called wet facade.

Surface preparation

Before gluing the insulation, the wall surface must be cleaned of fragments of the masonry binder protruding from the seams. For some types of bricks and PCBs, sanding is recommended, aimed at knocking down the glossy layer. You can check the surface for readiness for pasting with ordinary wetting: if water is immediately absorbed and does not drip off, you can apply glue.

To prevent the formation of mold and mildew, it is recommended to treat the supporting layer of the wall with a primer with the addition of an antiseptic. Primer of any type guarantees high-quality adhesion and almost completely eliminates peeling of the insulation belt, increases the durability of the finish.

When pasting walls of PPP, rough plastering is also widely used. It is carried out with the usual sand-cement mixture of grade 200 or 250. Often, plastering occurs right along the construction of the wall, while the masonry material picks up moisture from the binder solution and has high adhesion.

The main criterion of the wall for pasting is flatness. The presence of small irregularities is possible – they will be eliminated with a layer of glue and insulation plates. However, protruding fragments of any kind are unacceptable..

Installation of insulation boards

PPS boards are fixed to the bearing layer with an adhesive solution with polymer components. Temporary fixation against slipping is carried out with disc dowels, which, after the glue dries, have almost no benefit.

Special facade adhesives are used for gluing foam plastic – from the most popular and expensive Ceresit CT 83, 84, 85 to cheap analogs like Kreisel, Polimin and Siltek. The required properties of the glue are determined both by the type of the supporting base and by the stated requirements for frost resistance.

The glue is applied to the wall with a spatula or trowel and rubbed thoroughly into the surface, leaving a thick layer. After that, the wall is leveled with a comb with a tooth height of up to 15 mm. The slabs are mounted in the direction from bottom to top, the bottom row is supported on the protruding foundation with distance wedges.

When gluing the foam, it is not pressed down immediately, instead, 3-4 plates are pressed at once with a wide bar in different directions. The pot life of the glue mixture is 30–40 minutes and this leveling method ensures good surface flatness. When the slabs are aligned, they are fixed with disc dowels with a non-expansion part length equivalent to the thickness of the insulation. There are few fixation points, the standard step is 40-50 cm staggered.

Protective plastering

To exclude punching and mechanical damage to the foam, it is covered with a thin crust of protective plaster. In the simplest case, an ordinary sand-cement mixture is applied with the inclusion of plasticizers with a layer thickness of up to 20 mm. Special compounds can also be used, such as Knauf Rotband, Ceresit CT 72 or 74 facade plaster in a layer from 3 to 10 mm.

Special mixtures are used in cases where the building needs to stand for some time before applying decorative finishes. Also, the facade plaster can form a finished surface that does not require finishing, such as, for example, using the Ceresit CT 36 mixture. However, usually plastering is carried out with the gluing of the facade reinforcing mesh, and here a multi-layer application is necessary..

For gluing the mesh, the same adhesive mixture can be used that was used to fix the PPS boards. It is rubbed in a thin layer with a continuous vertical strip, the width of which is 10 cm wider than the width of the mesh used. The latter is applied to the fresh composition and carefully smoothed with a spatula, after which it is coated and pasted over the adjacent area with an overlap of at least 50 mm.

Facade finishing compounds

After the mesh has dried, the surface is thoroughly primed and cleaned of protruding streaks and other plaster defects. The final coating can be done with any type of finish with high vapor permeability.

Pebble plaster “Bark beetle” and the above-mentioned mixture Ceresit CT 36 behave in the best way. If the reinforcing mesh was masked with a sufficiently thick layer of plaster, for example, gypsum “Rotband”, the facade can be finished with paint. In this case, it is recommended to use hydrophobic vapor-permeable paints based on acrylates or latex polymer..

The finishing does not require any additional processing after drying. The appearance of whitish spots is possible, but they can be easily removed with plain water from a hose or disappear by themselves in 3-4 torrential rains. During operation, the facade can be re-painted an arbitrary number of times, which does not affect the heat-saving properties of the finish.