Choosing natural stone: from sample to quarry

Natural stone is one of architecture’s oldest and still most honest materials. But choosing stone for a project is not like picking a colour from a catalogue. Two travertines bearing the same name can look completely different when they come from different quarries, or even different veins of the same quarry. So we have a rule in the studio: we never choose a stone from a 10-by-10-centimetre sample alone.

A small sample shows only one moment of a stone. Across an entire floor, the veins, colour variations, voids and fossils come together to form a quite different texture. Choosing travertine for the Rock House, we went to the quarry three times and in the end chose not a block but a specific vein. Every floor slab was cut from that vein and the laying sequence was set by drawing. The result is a calm surface flowing uninterrupted through the house.

Surface finish fundamentally changes a stone’s character. A polished surface deepens colour but shows every scratch and water mark; a honed surface is matt and soft and more durable in daily use; brushed or tumbled surfaces resist slipping and bring out texture. In wet areas and outdoors we always check slip resistance. Using the same stone inside and out with different finishes is one of the most elegant ways to soften the threshold.

Local stone is both an ecological and a cultural choice. Marble from a distant country carries a large carbon load in transport; stone from a local quarry ties a building to its place. The walls of the Olive Grove Courtyard House were built in the region’s limestone; the same stone is found in the old houses of neighbouring villages. Though the building is new, its material says it belongs to this landscape.

The thickness and size of stone is a structural decision as well as an aesthetic one. Three centimetres may be enough for a facade cladding; but for a stair tread or cantilevered worktop the stone itself becomes structural. In setting slab sizes, we consider together the block sizes the quarry can extract, transport, and whether pieces can be handled on site. Large slabs are impressive, but if one breaks at a corner it is not always possible to find a replacement from the same vein.

Stone ages, and that has to be accepted. A lemon stain on a kitchen counter, the soft hollow worn into a threshold by years of footsteps, moss on a courtyard paver — these are not flaws but the life of the material. When clients choose a stone, we try to show them not only its first-day appearance but how it will look in ten years. To do so we visit old buildings together and see on site how the same stone has changed over time.