Natural Stone Selection pt.1: practical advice for designers and companies

The selection of natural stone in construction projects must be based on method, awareness, and scientific and technical knowledge.
Today, the market offers a vast range of natural stones that undergo various transformations and treatments to make them versatile and applicable in numerous contexts, modifying their characteristics and performance.

Personal taste, dictated by increasingly complex aesthetic and architectural demands, now clashes with the functional needs of a building and, in general, of a structure where the stone element dominates, neglecting the primary objective which is to design with sound judgement, execute well, and preserve the work from deterioration.

Unlike artificial materials, such as industrial composites where it is possible to create products with a certain uniformity and repeatability, each type of stone can carry with it variations in colour, texture, vein patterns, and the presence of inclusions. It is these peculiarities that make natural stone sometimes unrepeatable, even within the same geological formation. This change of “facies” defines its scientific classification and, above all, its commercial name.

We understand, therefore, that the concept of “uniformity” becomes naturally abstract, but the important thing is to guarantee homogeneity with awareness and honesty towards designers and clients, stipulating agreements through clear informed consent among all parties involved.

When we choose a natural stone for cladding, it is not enough to evaluate a single, isolated sample.

One must consider how elements such as the following present themselves as a whole:

• Colour
• Presence of impurities associated with variations in colour and aesthetics
• veining
• laminations
• cavities
• finishes
• surface treatments

Slab of marble with a polished finish characterised by veining and orange halos due to the oxidation of present impurities, likely sulphides.

It is essential to observe a set of reference slabs, of such size and variety as to be representative of the material in its entirety (Fig.2). Only in this way is it possible to appreciate the final result, that is, how the cladding will appear once installed in a real project. The observation must take place in natural light, from a distance of about two metres, as someone viewing a cladded wall would do, as prescribed by the EN 1469 standard

Mock-up for the overall observation of a cladding with reference samples.

These aspects should never become a cause for dispute after installation unless the non-homogeneities and irregularities are disproportionate to the reference sample. To avoid this, it is always advisable to be guided by a professional in the selection of the stone, especially if it has complex textures or is susceptible to chromatic alteration.

Therefore, choosing consciously means enhancing the authentic beauty of the stone.