External Thermal Insulation (ETICS) is an excellent system, but its external pasty render does not stay new forever. After 10-15 years of exposure to the sun, rain and exhaust fumes, the surface loses its gloss, fades and may show small hairline cracks or mould stains.
The building is asking for a renewal. The trap, however, lies in the fact that an external insulation system is not painted like a conventional concrete wall. If you use the wrong paint, you can literally destroy the entire insulation. Let's see how you can refresh your home while protecting your investment.
As we have analysed in previous articles, the success of a facade lies in the word breathability. The wall must act like the GORE-TEX membrane in sportswear: keeping rainwater out, but allowing the home's water vapour to escape.
Many owners, in their attempt to "seal" the cracks, ask for their ETICS to be painted with heavy, 100% elastomeric insulating paints (the ones that turn into rubber) or with very cheap, thick acrylics. These paints have a very high Water Vapour Diffusion Resistance index (Sd).
They create an impermeable membrane (like a plastic bag) over the render. When the moisture from the house tries to get out (or when the wall is heated by the sun), the vapour will be trapped behind the paint. The result? Nightmarish blisters (blistering) and complete peeling of the new paint in less than a year.
For repainting external insulation, the material must be certified for use over ETICS systems. The options are specific:
They are the "king" of repainting. They offer unbeatable breathability, while simultaneously being extremely water-repellent (rainwater forms "beads" and rolls off, washing the wall - the so-called "Lotus effect").
A more economical, but reliable solution. They offer great elasticity and sun resistance, but lag slightly in breathability compared to silicone paints.
If your old ETICS was light-coloured (e.g., beige), it is forbidden to repaint it in a very dark colour (e.g., anthracite or black)! Dark colours absorb huge amounts of solar radiation. The facade temperature will skyrocket to 75°C-80°C, melting the polystyrene insulation boards internally and breaking the render.
📐 Rule: The paint must have a Light Reflectance Value (LRV) greater than 25%, unless you use specialised "Cool Colors" technology paints.
It's not enough to just open the tin of paint. The substrate needs preparation:
The system has gathered dust and maybe fungi (green algae). Wash the surface with water under low pressure (do not use a strong pressure washer because you will cut the old render). If there are fungi, spray a special biocide / fungicidal liquid, let it act and rinse. Let the wall dry completely.
Inspect thoroughly for cracks. Do not use standard filler! Hairline cracks in ETICS must be filled with exterior elastomeric polyurethane or acrylic mastic.
The old, weathered render has become porous (friable). It needs to "bind" again before accepting the new paint. Use a micromolecular acrylic or silicone primer (water or solvent based, depending on the condition). The primer will penetrate deeply, stabilise the chalking (the dust) and create the perfect bonding base.
Apply the certified silicone or acrylic paint in two coats, strictly observing the drying times specified by the manufacturer between coats. Using a roller with the correct pile length (so the paint gets into the "rough" texture of the render) is essential.
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