Keim Mineral Silicate Paints for London: Conservation, Heritage Buildings, and Exceptional Longevity
How Keim mineral silicate paints work, why they're specified for London conservation areas and heritage buildings, the application process, colour range, and cost versus lifespan comparison.
What Keim is and why it performs differently
Keim is not a conventional paint. It is a mineral silicate coating — a product whose binder is potassium silicate (water glass) rather than the acrylic, vinyl, or alkyd polymers used in conventional paints. This matters because the binding mechanism is fundamentally different: rather than forming a surface film, Keim chemically bonds with the mineral substrate beneath it through a process called silicification.
The result is a coating that does not peel, crack, or blister. It cannot lift away from the substrate because it has become part of it. On masonry, render, and stucco substrates this means a lifespan of 20–30 years without recoating — compared to 8–12 years for the best conventional masonry paints applied to the same surface.
For London building owners, that longevity changes the economics significantly.
Why conservation officers specify Keim
Keim was developed in Bavaria in the 1870s and has been used on heritage buildings across Europe for 150 years. It is specified by English Heritage, Historic England, and conservation departments at numerous London boroughs because it addresses two problems that conventional paints create for historic masonry:
Breathability: Old masonry — Portland stone, stock brick, lime render, traditional stucco — needs to breathe. It holds moisture internally and releases it gradually. A conventional impermeable paint film traps moisture, leading to efflorescence, spalling, and frost damage. Keim is highly vapour-permeable (sd value below 0.01 m), allowing moisture movement through the substrate without restriction.
Surface filming: Conventional paints build up successive layers that eventually obscure the texture and detail of historic stonework. Keim's very low film build — 80–100 microns over multiple coats — preserves surface texture and carved detail even after decades of recoating.
In London conservation areas, particularly on listed buildings in Westminster, the Royal Borough of Kensington and Chelsea, and Camden, Keim is often the only coating that will receive planning consent for exterior application.
Application process: what to expect
Keim application is more demanding than conventional masonry painting and should only be undertaken by decorators with specific experience of the product.
Surface preparation: The substrate must be clean, sound, and free from organic growth. Loose or friable areas must be cut back and repaired with a mineral-compatible filler. Keim is not compatible with surfaces that have been previously coated with conventional impermeable paints — these must be fully removed before application, which can be a significant undertaking on London properties with multiple layers of historic paint.
Primer: Keim Universalgrund (or equivalent) is applied first to stabilise the substrate and regulate suction. This is a critical step — uneven suction produces uneven colour absorption in the topcoat.
Topcoat: Keim Granital (for exterior masonry) or Innostar (for smoother interior and exterior surfaces) is applied in two coats. The working time is shorter than conventional paint — the product must be applied at a consistent pace across each section to avoid lap marks.
Colour: The pigments in Keim are inorganic mineral oxides. They do not fade under UV radiation, which is why Keim retains its colour far longer than organic-pigmented conventional paints. The colour range is wide but must be specified in advance — Keim products cannot be tinted at the point of application.
The colour range
Keim's standard colour card runs to over 150 colours across the Ecosil, Granital, and Innostar ranges. Colours skew toward natural mineral tones — ochres, siennas, warm whites, stone greys — which makes them naturally sympathetic to period London buildings.
Custom colour matching is available but requires a lead time of several weeks. For conservation area work where the colour must match an existing or historically documented specification, the custom service is essential.
Cost versus lifespan: the honest comparison
Keim is expensive per litre — typically three to five times the price of a quality conventional masonry paint. Application is more labour-intensive. The total installed cost of a Keim specification is therefore substantially higher on day one.
Against that: a Keim application will typically last 25–30 years on a London masonry exterior before recoating is required. A conventional masonry paint in the same location requires recoating every 8–12 years. Over a 30-year period, the Keim specification frequently costs less in total, particularly when you factor in the disruption cost of scaffolding a central London property repeatedly.
For listed buildings, conservation area properties, and building owners with a long-term view of their asset, Keim is the rational specification.
Is Keim right for your London property?
Not every property needs Keim. For interior redecorations, rental properties, and new or modern exteriors, conventional paints are entirely appropriate. But for listed buildings, properties in conservation areas, or any exterior that has suffered repeated paint failure, the mineral silicate approach solves the underlying problem rather than masking it.
Contact our team or request a free quote to discuss whether Keim is the right specification for your project.