Façade paints

The colour coating of exterior facades plays a major role in determining the external appearance of a building and at the same time protects the underlying component layers from the effects of the weather.

When selecting the coating system, therefore, in addition to design considerations, the material properties are also decisive, such as water vapor permeability, protection against water penetration and material compatibility with the substrate.

More about façade paints

Before deciding on a coating system, all essential requirements should be analysed on a project-by-project basis, including in particular:

• (in)compatibility of the existing substrate with certain coating systems,
• required water vapour permeability/protection against water penetration, also in comparison with the coating substrate,
• Existing defects in the substrate (salt/moisture load, cracks),
• requirements under monument protection law,
• possibilities/restrictions of the individual coating systems in colour design,
• (approval-related) determination of certain products from a manufacturer, e.g. in the case of coatings as part of a thermal insulation composite or renovation plaster system,
• increased exposure to the weather,
• planned execution period with temperatures below 8°C
• Increased requirements for resistance to contamination.

Notes on

planning colour design: In addition to manufacturer-independent colour systems (e.g. RAL, NCS, LCH), many manufacturers also offer their own systems for façade paints, which take into account a particularly large selection of possible colour nuances, taking into account the manufacturer's available shades. For these ink systems, the manufacturer offers colour fans in which the colours are usually printed on matt sanded paper in order to obtain a realistic colour impression. The individual colours usually also contain information on the respective light reference value of the colour shade and the suitability of the colour shade for the various materials (e.g. emulsion paint, silicone resin paint, silicate paint). There are also programs and tools for color design on the websites of many manufacturers.

In the tender specifications, the intended light reference value of the paint must always be stated in the specifications, as this influences both the paint price (darker colours require a higher proportion of tinting colours and are therefore usually more expensive) and may also require additional measures, e.g. multiple coats of paint, or additional reinforcement measures such as diagonal reinforcement or full-surface reinforcement in the case of the preceding plastering/ETICS work. Fabric filling. Further explanations can be found on page ► 303│Exterior plaster – top plaster under Surface colour, light reference value.

Since even small nuances of colour have a significant influence on the effect of the façade in façade paints, it is always advisable to create alternating sample areas before making a final decision on a colour. If VOB C DIN 18363 is part of the contract, both the submission of prefabricated surface and colour samples and the production of up to 3 sample areas, each up to 1 m² in size, are ancillary services that are not to be remunerated separately.

Application process: The paint is applied by painting, rolling, or in the particularly economical low-mist airless spraying process, in which the surfaces are then re-rolled for a uniform surface appearance.

Silicification: Façade paints containing potash water glass, e.g. silicone resin paints, silicate paints and emulsion silicate paints, form an indissoluble and therefore particularly strong and permanent bond with the substrate through chemical silicification. However, this also makes it difficult to remove the coating later, which is only possible by destroying the substrate surface.

Damage-preventing surface treatments: The properties of façade coatings can be further improved by special surface treatments, e.g. to prevent damage caused by wall moisture or fungal/algae growth even better:

• Film preservation against algae/fungal infestation: Biocidal substances are added to the façade paint, which reduce or delay an infestation with algae and/or fungi, the use of the biocidal paints indoors is not possible for health reasons. The manufacturers point out that a permanent avoidance of algae/fungal infestation cannot be guaranteed according to the current state of the art, even with biocidal film preservations.
• Hydrophobic treatment: Mineral coating surfaces in particular have a relatively low basic protection against water penetration. This can be significantly improved by applying a suitable hydrophobic agent. As a rule, the water vapour permeability is only marginally deteriorated.

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Weather conditions: The manufacturer's specifications must be taken into account. Without special measures, painting work may only be carried out within the temperature and humidity ranges specified by the manufacturers for the respective product.

Substrate pretreatment: Many damages to façade coatings can be traced back to inadequate or missing substrate preparation. In any case, the substrate must be load-bearing, dry, clean, firm and dust-free. Any release agents present on concrete surfaces, e.g. formwork oils, must be completely removed, as well as cement haze or glassy sintered skin. In addition, the substrate must be free of unevenness that could affect the appearance or technical properties of the coating. According to VOB Part C, in this case DIN 18363 (painting and varnishing work), the executing contractor is obliged to inspect the substrate accordingly before starting his work and, if necessary, to register concerns about execution (without additional measures). Some of the measures listed below are special services for which the entrepreneur may be entitled to separate remuneration, details can be found in DIN 18363 VOB Part C.

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Standards and Literature

DIN 18363, VOB Part C, General Technical Terms and Conditions for Construction Services (ATV) Painting and Varnishing Work

DIN 55945, Coating Materials and Coatings - Supplementary Terms to DIN EN ISO 4618

DIN EN 459-1, Construction Lime - Part 1: Terms, Requirements and Conformity Criteria

DIN EN 1062-1, Coating materials - Coating materials and coating systems for mineral substrates and concrete in outdoor areas - Part 1: Classification

DIN EN 1062-3, Coating materials - Coating materials and coating systems for mineral substrates and concrete in outdoor areas - Part 3: Determination of water permeability

DIN EN ISO 4618, Coating materials - Definitions (ISO 4618:2006)

DIN EN ISO 7783, Coating Materials - Determination of Water Vapor Permeability - Shell Method (ISO 7783:2011)

BFS Leaflet No. 26: Color Change of Coatings in Exteriors, Status: 2007, Publisher: Federal Committee for Paint and Asset Protection e.V.

Source: bauwion