Not every facade paint satisfies all requirements equally well, which is why it is worth taking a look at the product data sheet or the processing guidelines before purchasing.
Just a few decades ago, facades were dominated by one color: gray. They consisted mainly of lime plasters to which cement was added for consolidation. Variations resulted from the structure; the plaster could be smooth or shaped, for example, it was available as trowel, rough or scratch plaster. Even today, many older houses can be found with facades that have withstood wind and weather for decades. If homeowners decided to paint their houses, they usually opted for the neutral white that used to predominate. These times are probably finally over.
Nowadays, facades shimmer in all conceivable tones; the once simple but also practical cold-cement plaster has long since given way to entire facade systems. Anyone who coats the exterior of their house with facade paint today wants above all for the coating to meet a number of requirements: it should cover well so that multiple coats are unnecessary, resist algae, fungus and moss growth, be breathable and adhere as well as possible. Essentially, the following products are available:
Dispersion paints are undoubtedly the big sellers on the market because they are easy to apply and comparatively inexpensive. As the name suggests, they consist of a very fine distribution of plastics (for example ethylene, vinyl acetate, styrene or acrylates) in water. Thus, they are not dissolved in it, but mixed in the smallest parts. If the water dries away after the facade paint has been applied, the coating forms a kind of film. Because there is a mixture anyway, color pigments are also well absorbed; consequently, emulsion paints are particularly suitable for colorful facades. They are also easy to repaint and largely breathable. It is better not to paint them on lime paints, lime-containing or difficult (porous) substrates.
Silicate paints are mineral paints and are also called water glass paints after their binder – liquid potassium silicate. They have a strong alkaline effect, do not contain any organic components and therefore offer nothing for algae or fungi to eat. They are mainly applied to cementitious and porous substrates, clinker and bricks or fiber cement. They literally bond with the substrate – this process is called silicification – and are particularly diffusible, i.e. permeable to water vapor, and resistant to acidic pollutants. Coatings of this type are known for their rich colors; however, since only waterglass-resistant pigments can be used, the selection of color shades is comparatively limited. These coatings can be repainted several times without any problems.
Lime paints tend not to be used for modern, highly thermally insulated and multi-layered facades. In the past, it was common practice in the countryside to whitewash farmhouses, stables and barns with paint based on slaked lime. Today, this paint is still used, for example, in renovations. It is alkaline, thus has a disinfecting effect, and is considered extremely breathable and ecological. However, lime paint is not very color-intensive; therefore, it is primarily suitable for pastel shades. Lime paint holds particularly well on still damp lime plasters, where it can dry slowly. Facades are pre-painted with milk of lime, followed by two to three coats of paint. To increase the wipe resistance, you can mix in table salt, linseed oil or even curd.
Polymeric resin paint
Polymer resin paints are not based on water, but contain solvents; they are usually bound by acrylic resins. They are therefore not suitable for lightweight and thermal insulation plasters containing polystyrene. However, they adhere particularly well to mineral plasters, brickwork or concrete, and emulsion paints. They adhere very strongly, really penetrate the substrate and solidify it. Because they do not contain water, they can still be used at low temperatures – winter construction sites.