Conservation of render and plaster

Mineral-based and silicate-based paints

Silicate paint has been on the market for more than 130 years, and this makes this surface treatment a natural choice when renovating a façade. The chemical bonding with the substrate together with its damp-diffusion openness and mineralic lustre is a perfect match for many buildings.

Protection of substrate and colour

Today, one-component silicate paints are applied all over the world on buildings dating from the last 130 years. Compared to lime-based paints, silicate reacts chemically with the substrate and forms a chemical layer several millimetres into the substrate. This chemical bonding ensures that there will be no peeling due to lack of adhesion. The extreme damp diffusion openness (low Sd value) ensures that no moisture is trapped, creating perfect conditions for the lime-based render. The paint itself is based on potassium silicate (water glass), the pigments are earth-bound or inorganic, ensuring colours that are UV-stable and non-leaching. Since the paint is mineral-based, it has no lustre, but yields a matt surface with a high water retention, giving it the living surface also known in lime-based paints. In spite of this, the chemical reaction layer prevents driving rain from penetrating deep into the substrate.

The perfect fit for your lime-based render

Lime paint

Lime can work on different substrates. The best substrate though is a well-carbonated lime render. NHL-based and high lime LC mixtures are also suitable. The substrate should be repaired with the correct material and prepared to obtain the same suction over the whole surface. Different applying properties (suction, pre-treatment, applying method and hardening conditions) might give colour differences. Depending on the lime product to be used, pre‑treatment can include products that open the surface pores and after‑treatment with limewater to kickstart the carbonation process. A golden rule when applying is to use several thin applications of lime, followed by spraying with pure water. A final coat of limewater will fixate the lime and reduce smitting. As with all works involving lime, protection from fast drying, wetting and frost during the carbonation period is essential to obtain a long-lasting result. Depending on the local conditions, a silicate paint can last for several decades.

Silicate paint needs a mineral-based substrate consisting of lime and/or cement. It creates a chemical layer and should be used on NHL-, LC- or C-based renders. It is water-based and needs a well-hardened surface to be able to react properly and gain its optimal properties. In conservation it is important that all organic-based material (paint and oil) is removed before painting with silicate as it will not gain adhesion on surfaces containing organic matter. On new substrates, the render should be well-hardened with at least 14 days of hardening/carbonation time. Before applying, the render should be etched and application should be carried out using a brush to work it well into the substrate. Two layers is usually enough to obtain coverage. As silicate is sensitive to hardening conditions, planning is important to avoid shades. A steady temperature of above 5 degrees Celsius when applying is also necessary to start the hardening. Silicate can also be used to consolidate porous surfaces.