- Optimal working conditions
- Basic principles of technology
- The choice of insulation
- Surface preparation
- Installation of the starter bar
- Fastening insulation
- Decorative finishing
“Wet facade” for house insulation is a universal and affordable method. It can be used both for a building under construction, and for a long-operated one, including the insulation of the outer walls of the apartment. In this material, we will consider the criteria for choosing a heater, the structure of a wet facade and how to install it.
Optimal working conditions
The wet facade got its name thanks to the use of building mixtures: facade plaster, glue for fixing insulation and reinforcing mesh. Such a set of materials imposes restrictions on the average daily air temperature permissible for working with them. Standard lower limit without special additives for mortar + 5 ° C. Recommended temperature range: +15 ° C to +25 ° C.
If it is not possible to cover the entire work in one season, you can “mothball” the facade at the stage of insulation. Apply a layer of primer to the polystyrene, since the main “enemy” for it is solar ultraviolet light. And cover the mineral wool with plastic wrap. But these are unnecessary expenses, so it is better to carry out work on time.
Basic principles of technology
The technology is based on a sandwich construction of three layers:
- Rough facade, as a basis for fixing insulation.
- Decorative plaster.
A simple diagram of the “wet facade” device: 1 – wall base; 2 – adhesive composition; 3 – insulation; 4 – mechanical fasteners; 5 – reinforcing layer; 6 – decorative plaster
The choice of insulation
Before starting work, you need to choose a heater and calculate its optimal thickness. The choice of the brand of glue depends on the type of insulation, the width of the starting plate, slopes of windows and doors depends on the thickness.
There are three options for insulation for a wet facade:
- expanded polystyrene;
- extruded polystyrene foam, polyurethane foam;
- rigid mineral wool mats.
There are no fundamental differences between the first two types, with the exception of the method of mating sheets of material and the choice of an adhesive composition with maximum adhesion rates. Their thermal conductivity is approximately the same, but the water absorption of extruded polystyrene foam is lower, and the strength is higher, so many people prefer to use it (although it is more expensive).
The disadvantage of expanded polystyrene is flammability, although it does not apply to flammable materials. For insulation, it is necessary to use sheets marked PSB-S (self-extinguishing), and under a layer of plaster and with a lack of oxygen, even for smoldering, inappropriate conditions. Therefore, the only “contraindication” for insulation with expanded polystyrene is “breathing” wall materials.
The vapor permeability of expanded polystyrene is low (even less for extrusion), and its installation levels the ability of the walls to natural gas exchange between the room and the street. You can, of course, not pay attention to this, especially since the main load on gas exchange is placed on the system of natural or mechanical ventilation, but there is such a thing as “moisture transfer”, and it is very important for the strength and durability of the structure. It is important to follow the general rule: the vapor permeability of multi-layer enclosing structures of residential buildings should decrease as we move from the inner layers to the outer ones..
With external insulation, the dew point shifts towards the insulation. If it acts as a vapor barrier, and the vapor permeability of the walls is high, then in cold weather this will lead to the appearance of moisture in the form of condensate and its accumulation on the wall surface and in the construction materials. In the warm months of the year, this excess moisture should evaporate, but again a vapor barrier in the form of a heater will stand in its way. Moisture simply does not have time to disappear, excess will lead to the formation of mold, loss of building properties of materials, and, as a result, to the destruction of the wall structure.
For heat-insulating plastering systems, only mineral wool boards can be used that can withstand a pull-off load of the upper layers of at least 15 kPa. These include hard slabs of mineral wool according to the domestic standard with a brand index of at least 175 or mineral wool of imported brands, intended for facade work, with a density higher than 125 kg / m3.
Mineral wool, in addition to breathing properties, is also a non-combustible material, but this is where its advantage over expanded polystyrene ends. It has one and a half times higher thermal conductivity and a fairly high hygroscopicity, and as moisture accumulates, thermal conductivity increases and thermal insulation properties deteriorate. The ventilation gap is responsible for the removal of moisture in the hinged facades, and in the wet facade the condensate must escape through the layer of plaster. If the vapor permeability of the plaster is low, then the insulation will “get wet”. Therefore, acrylic facade plaster cannot be used for mineral wool in the finishing decorative layer..
To calculate the thickness, it is better to use an online calculator. To find out the thickness of the insulation, you just need to enter the initial data: the thickness of the wall and the type of materials, the thickness of the plaster layer, the region (or the standard indicator of the heat transfer resistance of external walls) and select the type of insulation. Then the resulting value is rounded up to the nearest selling thickness of the selected insulation.
Important! If there is no insulation of the required thickness on sale, then in no case should the insulation be carried out in two layers (no matter what they say about overlapping the second layer of the seam as a cold bridge). Non-monolithic vertical construction of two layers of “soft” slabs, loaded with a layer of plaster, can behave unpredictably under the influence of temperature and humidity changes.
It is necessary to remove everything unnecessary from the surface of the facade: lamps, attachments, mechanical fasteners for laying engineering communications (brackets, clamps, consoles). Free the wall sections adjacent to the window and door openings – remove the ebb, canopies and awnings, roller shutter boxes.
If the walls are painted, the paint must be cleaned. Check the plaster for weak and crumbling areas. They wash off or clean up oil stains, efflorescence, dirt, rust traces – all this impairs the adhesion of the wall and glue. Inspect the facade for mold and mildew. Problematic areas are cleaned and treated with antiseptic compounds.
Cracks close up. After that, the surface is leveled and primed.
Important! Cracks should be repaired according to all the rules: it is necessary to establish its nature, find out the causes of occurrence, take measures to eliminate the causes.
Installation of the starter bar
To mount the starting strip, it is necessary to beat off the level of the fastening line. Moreover, it must be remembered that the attachment line is several millimeters above the shelf level.
The insulation itself should be located like this:
- for a strip foundation and a basement in the same level with the wall, so that it covers the floor slab of the first floor (but not lower than 40 cm from ground level);
- for strip foundations and protruding plinths – on the line of the plinth;
- for pile and columnar foundations – below the level of the subfloor and overlapped its insulation.
When insulating the whole house, the level of the line of fastening of the starting plate along the perimeter should converge to “one point”. The distance between the ends of adjacent strips must be at least 3 mm (to compensate for thermal expansion).
The mounting plate supports the first layer of panels.
A layer of a previously prepared adhesive solution is applied to the inner surface of the board. If the surface of the wall is relatively flat (the difference in the heights of irregularities is not more than 5 mm), then it is applied evenly over the entire slab and “profiled” with a notched trowel.
For an uneven wall, the solution is applied to the insulation along the perimeter of the wrong side of the plate (two centimeters from the edge) and pointwise, in the form of cakes, on the rest of the surface, having previously covered it with a thin layer of glue. For mineral wool, this layer must be literally rubbed into the surface. The total area of strips and cakes should be at least 40% of the area of the plate. The thickness of the cakes and the perimeter layer must be greater than the height difference of the wall irregularities.
Then the slab with glue is inserted into the starting plate and pressed against the wall, leveling it along the vertical level. Excess glue protruding at the edges is removed.
In the same way, the remaining plates of the first row are fixed, adjusting them as tightly as possible to each other and leveling their overall surface level (the height difference at the junction of two adjacent plates should not be more than 3 mm).
The second row begins with an offset relative to the first. Usually the offset is equal to half the sheet, but not less than 200 mm. This clarification is important when passing openings. The difficulty of traversing openings is that their corners should not lie in the intersection of the slabs. In other words, the angle of the opening should not coincide with the seams of the slabs either vertically or horizontally, but it must be cut out in the slab.
The plates are additionally fixed with mechanical fasteners. For a low-rise building, there should be at least 5 dowels per square meter. One fastening in the middle of the “square”, the rest in the corners (the distance from the edge of the plate to the dowel is at least 5 cm).
To prevent the decorative finish from cracking in the area of the seams, the surface of the insulation is reinforced with a fiberglass mesh. To do this, a 3 mm thick layer of adhesive solution is applied to the surface of the slabs (to compensate for the difference in height between adjacent slabs), after which the mesh is pressed into it. The mesh strips should overlap – at least 10 cm.
The corners cut in the insulation for the openings are reinforced with an additional strip of fiberglass, laid at an angle of 45 ° relative to the upper cut of the opening. Additionally, the joints of the slabs on the outer and inner corners of the facade, as well as the edges of the slabs in the openings, are reinforced with a perforated corner. Then, on top of the mesh and corners, another layer of 3 mm solution is applied and smoothed.
After the layer of reinforcing mortar has dried, it is rubbed over and decorative finishing is started. To do this, use ordinary or decorative plaster..
The technology for applying a decorative layer depends on the type of plaster, surface condition and manufacturer’s recommendations.