- What is the essence of wet facade technology
- Requirements for the strength of the base
- Installation of insulation system
- Surface preparation for finishing
The method of exterior decoration of a building directly depends on the thermal properties of the enclosing structures and their structural features. Today we will tell you where it is advisable to use the wet facade technology, what are its advantages and how to properly arrange the finish in this way..
What is the essence of wet facade technology
A wet facade is a method of insulation, which involves plastering walls over a layer of insulation. In general, the wall cake consists of three layers: insulating, basic and protective and decorative. The range of materials used in each of them is wide enough, which is the reason for the high versatility of the system for different types of bearing bases.
Wet facade cake: 1 – load-bearing wall; 2 – glue for insulation; 3 – insulation; 4 – disc dowel; 5 – base layer of plaster; 6 – reinforcing mesh; 7 – finishing layer of plaster; 8 – decorative trim
The dominance of new manufacturers of construction chemicals and materials for insulation on the market makes the behavior of facade decoration unpredictable during the first 3-5 years of operation. The main danger is posed by cracks arising from insufficient quality preparation of the base and violation of the work technology. There is also a risk of violation of the vapor permeability of the walls with an aggravation of the state of the supporting layer of the enclosing structures.
The technology of a wet facade is not inferior in popularity to other insulation systems, although it is mistakenly perceived as primitive. The quality of appearance and durability entirely depend on both the correct choice of materials and compliance with the basic installation rules. Many are encouraged by the opportunity to arrange the facade decoration by choosing a suitable set of materials, however, the thickness of the insulation and the composition of the surface layers must be carefully selected according to the data of the heat engineering calculation, otherwise the risk of damage to the supporting structure is too great.
Requirements for the strength of the base
Unlike panel insulation systems, a wet facade has fewer requirements for the quality of leveling and base preparation. However, in order to securely fix the insulation, the wall must have good adhesion and have a hard, durable crust in the form of a preparatory plaster layer. It is a bad idea to level the walls with insulating materials, because the more uniform the thickness of the layers of the cake, the better the behavior of the walls during operation..
Although the facade subsequently has a layer of insulation of a sufficiently large thickness, acting as a damper of linear deformations, it cannot be guaranteed that the formation of cracks and seasonal deformation of the walls will not affect the appearance. The main threat when insulating with incompressible materials is the swelling of the walls and ruptures of the preparatory layer from uneven settlement and curvature of the foundation. On mineral insulators, such phenomena are not reflected so strongly, but there is a directly opposite problem – the quality of fastening heat protection to the base.
It is considered optimal for stone houses to apply plaster without reinforcement with a layer of about 10-15 mm. For buildings of frame type or made of SIP panels, it is widely practiced re-cladding with sheet materials: OSB 3 class 8–10 mm, FSF plywood 5–7 mm or GVLV-superlist, if necessary, maintain vapor permeability. Installation of sheets should be carried out with overlapping of the junction of panels or joints of the sheathing of the bearing layer. If it is necessary to improve adhesion, the walls are covered with a facade primer containing quartz dust.
We also draw attention to the prospect of finishing with a wet facade should be taken into account when determining the width of the foundation tape and the location of the wall on it. The plinth of the building should have an external ledge to support the exterior decoration cake. At the same time, it is allowed to refine the basement in other ways..
Installation of insulation system
Fastening of the insulation to the wall is carried out both mechanically and by glue. To achieve a high quality finish, not only the real characteristics of the adhesive mixture are important, but also the correct choice of insulation material with the appropriate installation technique. In general, the technology of a wet facade allows the creation of a thermal protection belt up to 150 mm thick.
The choice between polymeric foam and mineral insulation is determined by the thermal engineering calculation of the building, as well as the type of base on which the insulation material will be glued. In general, there are two options to eliminate the threat of condensation in the insulation and the base layer:
- Use insulation with low water absorption, the layer thickness of which is large enough so that the dew point shift range is entirely within it.
- Use a vapor-permeable insulation (mineral wool), the thickness of which allows condensation only at the surface itself, from where moisture can freely evaporate through the finishing layer.
In the latter case, the implementation of the project is fraught with a number of difficulties. First, it is necessary to ensure that the finishing material will have a vapor permeability equal to or higher than that of the insulation layer. The second problem is that the final thickness of the insulation may simply not be enough to achieve the desired thermal conductivity of the walls..
When applying a wet facade, the insulation is attached without installing a subsystem. The main function of fastening is performed by glue:
- for expanded polystyrene – on a cement basis with the inclusion of microfiber such as Ceresit CT-85 (CT-83), KREISEL 210 (220);
- for mineral wool – also cement-based reinforcing glue, but with a high steam permeability: Ceresit CT-190, POLIMIN P-20, ideally Caparol Capatect Klebe – 190.
Dry mixtures are not used for gluing expanded polystyrene to sheet materials. You can use ready-to-use dispersion compounds like Ceresit CT-100, but adhesive foam traditionally has the best adhesion and resistance to heat transfer.
Fastening of thermal insulation in both cases should be done in two ways – glue (along the perimeter of the plates and pointwise along the plane) and disc dowels (at least five points, in the corners and in the center). In addition to the fact that mechanical fixation provides a tight pressure for the period of glue setting, it prevents the insulation from tearing off and relieves part of the load from the adhesive layer. The glue, in turn, well resists the displacement and subsidence of the insulation under its own weight, reliably seals the joints between the plates, and most importantly, it excludes air microcirculation under the insulation.
Surface preparation for finishing
After fixing the thermal protection, the base layer is applied. It must be reinforced with a facade fiberglass mesh with a cell size of the order of 5–8 mm and a density of 150 g / m22. First, a thick (1.5-2 mm) layer of base plaster is applied to the insulation with a vertical strip 10–15 cm wide more than the roll, then a mesh is applied and smoothed, the edge of which is poured onto the previous strip of about 10 cell values. When the overlap is formed, the previous area is covered with a final layer of base plaster, which is smoothed out with a wide trowel and trowelled with an abrasive mesh after drying. If it is necessary to provide additional strength to the facade finish, the base layer is applied twice, respectively, with two layers of reinforcing mesh.
The composition of the base plaster is determined by the type of insulation used. For expanded polystyrene boards, only adhesion is important, so you can use dry mixes for fixing the boards to the base or warm plaster. For mineral insulation, it is important to maintain vapor permeability. You can also use glue for mineral wool, but plasters that support gas exchange are better recommended: Ceresit CT-174, Atlas Cermit and the like. Plaster can be either a finished finish or serve as a preparatory layer for thin-layer application.
The application of a layer of base plaster should be carried out as soon as possible after the installation of the insulation. An open heat protection belt is very vulnerable to weathering: mineral wool is afraid of moisture, polystyrene foam – sunlight and mechanical stress. After the basic plaster has been applied, there is time for a breather and a decision: whether the decorative finish will be applied and what it should be?
At this stage, it is very easy to negate all the benefits of the technology. In particular, if the facade coating does not have the required hydrophobicity, moisture can penetrate into the decoration cake. If a layer of paint restricts gas exchange in the wall, then moisture condensation in the thickness of the mineral insulation or at the border of the adhesive layer is possible.
Among all types of finishing for a wet facade, stone plaster with a tinted base and painting with latex-acrylic compounds can be recommended. In the first case, it is possible to add texture to the surface and make the finish more interesting, since the technique of applying “rain” with “bark beetle” has been developed enough for today, including for non-professionals. Facade painting is much faster and requires less investment, but the paint composition must be compatible with the insulation and plaster-adhesive mixture used. It is recommended to pay close attention to ready-made complex solutions for wet facades from Ceresit, Caparol or KREISEL if they have representatives in the region where the construction is underway. The compatibility of such materials is not questioned, in addition, the manufacturer usually gives a guarantee and recommendations for the performance of work.