Marble on the Facade: Where It Fits and How It Behaves

Marble for facades is a possible but demanding choice. It is a metamorphic rock of recrystallised calcite or dolomite: beautiful, dense and easy to polish, but outdoors it loses its shine, is sensitive to acid rain and can deform when cut thin.

The key criterion is the specific type of marble and the operating conditions: dense, fine-grained grades with low water absorption and proven frost resistance suit facades, while decorative grades with many veins and cracks are best kept for interiors.

Marble is chosen by architects and clients who want a prestigious look: for portals, columns, cladding of the lower floors of public buildings and mansions. More on other rocks in the section Natural stone for facades and interiors.

Marble forms from limestones and dolomites under high temperature and pressure. Calcite recrystallises, the stone becomes denser and acquires a granular crystalline structure that gives its characteristic depth of colour after polishing.

Values depend on the deposit; design uses data from the test report for the specific batch.

Marble facade cladding must take into account not only strength but also structure: grades with clay veins and open cracks carry a higher risk of failure along these weak zones outdoors.

How marble behaves outdoors is well known from historic buildings. The main processes are:

• Loss of polish. Rain, especially in cities, contains dissolved acidic oxides. Calcite slowly dissolves and the surface becomes matt and rough. That is why facades more often use a honed, ground or matt finish, which ages more evenly.

• Soiling and darkening. A rough surface holds soot and dust; light marble gradually turns grey in an urban environment.

• Slab deformation. Calcite crystals expand unevenly when heated and cooled. For thin slabs on sunny facades this can lead to irreversible bowing and loss of strength, a well-known effect that forced the marble facades of some high-rise buildings to be re-clad.

• Frost damage. If the stone is fractured, water in the cracks widens them as it freezes.

• Staining. Rust from steel fixings and cement mortars leave marks that are hard to remove.

The practical conclusion: marble outdoors is appropriate in moderate quantities (portals, columns, ground-floor cladding, details) and with sound detailing. For large facade surfaces in a cold climate granite is chosen more often, and the look of marble can be reproduced with glass fibre reinforced concrete (GFRC) or porcelain stoneware.

Marble slab thickness and fixing method are determined by calculation, taking into account flexural strength, slab size, wind load and building height. Guidelines from practice:

• for rainscreen facades marble is usually at least 30 mm thick; for large formats and at height, 40 mm or more;

• thin slabs (20 mm) are used indoors and adhesive-fixed in sheltered areas;

• on sunny facades with large temperature swings the thickness is increased to reduce the risk of deformation.

Fixing. On a facade marble is installed on a rainscreen substructure, with clips in edge kerfs or concealed undercut anchors on the back. All fixings are stainless steel or aluminium: ordinary steel rusts and leaves stains. Wet fixing on cement mortar is undesirable for exterior marble: moisture and salts from the mortar penetrate the stone and cause stains and efflorescence.

Movement joints are needed between slabs; horizontal surfaces (cornices, sills) are made with a fall and a drip so that water does not sit on the stone.

Indoors marble shows its full potential: there is no rain or frost, so polish and colour are preserved. The main applications are:

• walls and floors of halls, lobbies and lift areas;

• staircases and steps (with anti-slip inserts or a matt finish);

• columns, portals, fireplaces;

• bathrooms and hammams, bearing in mind that marble is sensitive to aggressive household chemicals;

• worktops and window sills.

On floors with heavy traffic marble wears faster than granite; for entrance areas of public buildings this is accounted for by choosing a harder grade or granite.

Interiors are a good place for decorative grades with vivid veining: their weak zones are not exposed to frost there. Such grades should not be taken outside.

Pattern continuity matters indoors: large slabs are laid book-matched or in a continuous vein pattern so that the veins run from slab to slab. Such a layout is prepared in advance from photos of the slabs, and cutting follows a cutting map.

Caring for marble is first of all about protection from acids and abrasives.

• wash with water and pH-neutral natural stone cleaners;

• do not use vinegar, citric acid, or acid-based limescale and rust removers;

• on facades, treat with penetrating water repellents and oil-repellent impregnations and renew them as they wear;

• to remove soot, use gentle methods: soft washing, special cleaners and, if necessary, professional restoration;

• polished interior surfaces are periodically restored by honing and polishing.

In winter, salt-based de-icers are not used near marble steps and plinths: they leave stains and accelerate the deterioration of the stone.

Marble is part of the TECHNOFORMA natural stone range; the company works with stone from India, Turkey, China and Iran and also supplies it to order from around the world. For facade solutions, specialists will help you choose between marble, granite and GFRC, which reproduces the look of stone at a lower weight.

An example of a facade with natural stone is the Dinastia club house in Kislovodsk: granite (700 m²), porcelain stoneware (700 m²) and GFRC (6,000 m²) were used for cladding; design and installation were carried out by the company. See all TECHNOFORMA projects and the article “Granite for facades and plinths” on the most durable facade stone.