Facade surface infested with algae and mould
| CLASS (EN ISO 1062) |
Sd |
| V0 |
No requirements |
| V1 - high vapour permeability |
< 0,14m |
| V2 - medium vapour permeability |
≥ 0,14m
<1,4m |
| V3 - low vapour permeability |
≥1,4m |
The lower the Sd, the higher the vapour permeability of the paint film.
Water permeability (water absorption):
It is expressed with the water absorption coefficient W24, which tells us how much water is absorbed by a paint film in 24 hours at a constant temperature and film thickness - it is expressed in kg/m2K1/2. The lower the W24, the lower the water absorption of the paint film.
| CLASS (EN ISO 1062) |
W24 |
| W0 |
No requirements |
| W1 - high water absorption |
> 0,5 kg/m2K0,5 |
| W2 – medium water absorption |
≤ 0,5 kg/m2K0,5
> 0,1 kg/m2K0,5 |
| W3 – low water absorption |
< 0,1 kg/m2K0,5 |
The lower the water absorption, the higher the water resistance of the coating.
Important functional properties of facade paints for renovation
In addition to vapour permeability and water absorption, there are many other important facade paint properties which allow for a good quality renovation of old facade coatings. The hairline micro-cracks that appear on old, worn coatings can be covered with a facade paint which contains fibres. The fibres are arranged in a lattice structure in the paint film matrix, which bridges the hairline cracks. A careful combination of quartz and carbonate fillers in different granulations is also important. These are evenly distributed in the binding matrix and give a uniform thickness to the coating, which is evenly protected with the binder over its entire surface. Quartz fillers increase the coating’s mechanical strength and thus its resistance to wear. As mould and algae often grow on old facades, which are more exposed to moisture, the renovation coating must contain a biocidal dry film protection which will prevent the growth of mould and algae on the renovated facade for a longer period of time.
The binder is an essential component of any coating. The amount of binder is more important than the type of binder. The role of the binder is mainly to protect the pigments and fillers. Binders deteriorate after a prolonged exposure to UV sunlight, followed by UV degradation and washing out of pigments and fillers. This can be recognised mainly by the fading of the colour shade, a blotchy appearance and the chalking of the coating. It is therefore very important that only inorganic pigments are chosen for the preparation of the shade, as they are more UV- and weather-resistant compared to organic pigments.
The choice of the colour shade is also important. If a darker shade is chosen, the absorption of thermal energy is higher and the pained facade surface heats up more than if the colour shade is lighter. During periods of greater day/night temperature changes, the colour film heats up and consequently stretches during the day, then cools and shrinks during the night. Conventional facade paints do not create a sufficiently elastic film to withstand a large amount of periodically repeated stretches and shrinkages, so darker shades more often lead to cracks, which are the beginning of the deterioration of the facade protection. Coatings manufacturers provide a Y value for each colour shade in colour charts. The Y value is a measure for the lightness or darkness of a shade. The Y value of white is 100 and that of black is 0. The higher the Y value, the lighter the hue, the less thermal energy it absorbs and the less it heats up. We do not recommend colour hues with a Y value less than or equal to 20 for facade surfaces. In our experience, even shades where the Y value = 50 become overheated.
The choice of facade paint for renovation depends on the type of the old facade coating
On facade surfaces which have been protected with a thermal insulation system based on extruded polystyrene (Styrofoam), the finishing layer is an acrylic dispersion plaster. These systems are characterised by medium vapour permeability and low water absorption. Acrylic facade paints which have commonly been used for the decorative protection of non-thermally insulated facade surfaces have similar properties.
In order to keep these two properties on the same level, SPEKTRA Facade Universal is used for renovation. In the case of thermally insulated facades with mineral wool or another highly vapour permeable insulation, silicate or silicone plasters are commonly used as a finishing dispersion plaster. These systems are highly vapour permeable and have very low water absorption. In this case we recommend SPEKTRA Facade Renoxan for the renovation, as it maintains both high vapour permeability and low water absorption due to its composition. It is also suitable for the renovation of highly vapour permeable and water resistant facade paints and mineral plasters. The composition of both facade paints provides long-lasting protection, as their composition meets all the above-mentioned requirements for the renovation of old, worn facade surfaces.
