Heritage Lime & Silicate Paint for Period Masonry in London: Keim, Beeck & Beyond

Why Standard Masonry Paint Is Wrong for Period Buildings

Walk down any Victorian or Georgian street in London and you will see the consequences of applying the wrong coating to period masonry: bubbling, peeling, damp trapped beneath the surface, and render that cracks because it can no longer breathe. Standard acrylic masonry paints — Dulux Weathershield, Sandtex, and their equivalents — are film-forming coatings. They sit on the surface of the substrate and prevent the passage of water vapour in both directions.

On a modern cavity wall with a sand-cement render, this presents few problems. On a solid-walled Victorian or Georgian building with a lime render or lime mortar, it is a long-term disaster. These old walls are designed to absorb driving rain, hold it temporarily in the mass of the wall, and then release it as vapour when conditions allow. Seal that release pathway with an impermeable film and you trap moisture inside the wall — causing salts to effloresce, render to hollow, and damp to migrate inward.

The correct materials for period masonry are lime washes, silicate paints, and silicate-dispersion paints. Here is how to choose between them.

Limewash: The Traditional Option

Limewash — simply water and slaked lime, often with a small addition of linseed oil or tallow to improve durability — has been used on British masonry for centuries. It is fully breathable, fully compatible with lime render and lime mortar, and if applied correctly will last five to eight years before it needs refreshing.

The limitations of limewash are real: it fades, it weathers unevenly (which can be a feature rather than a fault), and it is not suitable for surfaces that have been previously coated with a synthetic paint. Applying limewash over acrylic masonry paint achieves nothing — the limewash sits on top of the acrylic film and will peel off.

For a building being returned to traditional finishes after stripping old synthetic paint, limewash is the authentic choice. Brands worth specifying include Beeck Kalkfarbe, Earthborn Limewash, and Limebase Products Natural Limewash.

Keim Mineral Paints: The Professional's Silicate Option

Keim Farben, a German manufacturer established in 1878, produces the definitive range of silicate mineral paints. The chemistry is based on waterglass — potassium silicate — which reacts with the silica in the substrate to form a permanent mineral bond. Keim coatings do not form a surface film; they become part of the substrate itself. This means they cannot peel, blister, or trap moisture.

The main Keim products for period London masonry:

Keim Soldalit. Pure mineral silicate paint, suitable for lime render, natural stone, and pre-weathered concrete. The most breathable option in the range. Comes in over 200 colours. Requires damp, alkaline substrate for proper carbonation — do not apply to bone-dry surfaces in summer without pre-wetting.

Keim Granital. A silicate-dispersion paint — potassium silicate plus a small organic binder component (less than 5% by weight). More tolerant of surface irregularities than pure Soldalit, suitable for previously painted surfaces where the old paint is sound. The organic component slightly reduces breathability but still vastly outperforms any acrylic coating.

Keim Biosil. Interior-grade silicate paint for walls and ceilings where air quality and breathability are important — appropriate for listed building interiors.

Beeck Mineral Paints

Beeck is a second German mineral paint manufacturer producing products comparable to Keim, with a slightly different formulation approach that some decorators prefer for its handling properties. Beeck Quarzil is the direct equivalent of Keim Granital. Beeck Granomal is a silicate-based coating formulated specifically for textured masonry. Both offer excellent vapour permeability and long service lives.

Substrate Preparation for Silicate Paint

Silicate paints are unforgiving of poor preparation. They require a mineral substrate free of organic contamination, loose material, and film-forming coatings. The preparation sequence:

1. Remove any existing synthetic paint. Silicate paint will not bond over acrylic or oil-based masonry paint. Stripping options include Peel Away 7 (alkaline gel, suitable for render), pressure washing at moderate pressure (1,000–1,500 psi maximum on lime render — higher pressures cause damage), or mechanical preparation with a wire brush or needle gun.

2. Check for organic growth. Algae, lichen, and moss must be treated with a biocide — Ronseal Weatherproof or Keim Algicid — and allowed to die back before washing off. Do not paint over living organic growth.

3. Make good the render. Cut out hollow sections, rake back to sound substrate, and repair with a lime mortar (NHL 3.5 binder, sharp sand in a 1:2.5 ratio). Allow to cure for a minimum of four weeks before applying silicate paint. New lime render is alkaline and this is what the silicate needs — but it must be fully set.

4. Pre-wet the surface. Keim and Beeck both specify that the substrate must be damp before application. On a warm day, mist the wall with clean water immediately before applying each coat.

5. Apply two coats. Silicate paints are thin and translucent — single-coat application rarely gives adequate coverage. Two coats, applied with a brush (not a roller, which over-applies and creates streaks), are standard. Work section by section to avoid lap marks.

Service Life and Cost

A properly applied silicate coating on a well-prepared lime render should last fifteen to twenty-five years without significant degradation. Acrylic masonry paint, on the same substrate, commonly begins to fail within five to ten years — and its failure causes secondary damage that costs more to repair than the painting itself.

The material cost of Keim Soldalit is higher than Dulux Weathershield: approximately £60–£80 per five litres versus £20–£30. But when spread over a twenty-year service life — and when accounting for the damage avoided — silicate paint is the economical choice on any period masonry building.

Specify Correctly for Your London Property

If your property was built before 1920, has lime render, lime mortar, or natural stone, and needs exterior painting, the specification matters enormously. Contact us or request a free quote and we'll advise on the correct coating system and carry out the work to the standard these buildings deserve.