Travertine, quarry to threshold

We have used travertine on four projects in three years, and each time the stone that arrived was a different animal from the stone we approved. This is a note on how we stopped that happening.

The quarry decides more than the drawing

Travertine is a freshwater limestone laid down in beds, which means it has a direction. Everything about how it behaves — the pattern, the porosity, the way it takes a chamfer — follows from where in the bed it was cut and which way the saw went through it. Two slabs from the same quarry, the same week, can look like different materials.

The practical result is that specifying travertine by name is close to meaningless. You are not buying a material, you are buying a particular block, and if you have not seen that block you have not specified anything. For Casa Vetiver we flew to Tivoli and put chalk on the block we wanted. It added eleven days and about four per cent to the stone budget. It was the cheapest insurance on the project.

Vein-cut or cross-cut

Cut along the bed and you get vein-cut: long linear striations, a stone that reads as movement and direction. Cut across it and you get cross-cut: cloudy, open, closer to a section through a sponge. They are the same stone and they belong in different rooms.

We use vein-cut where we want the floor to lead somewhere — corridors, thresholds, the run from a door to a window. We use cross-cut where the stone should sit still: a bathroom floor, a hearth, a wide shelf. Mixing them in one sightline almost never works, and we have made that mistake so you do not have to.

One caution on vein-cut. Because the striations run one way, the stone is measurably weaker across them. On a threshold piece taking daily foot traffic we always run the veins along the length of the piece, never across it, whatever the pattern would prefer.

Filled, unfilled, and the honest middle

Travertine arrives full of voids. The supplier will offer to fill them with resin, which gives you a flat, easy, entirely uniform surface and removes most of the reason to have chosen travertine at all.

Unfilled is the other extreme. It is beautiful in a showroom and difficult in a kitchen, because every void is a small cup waiting for olive oil. We have specified it exactly once, in a hallway, and it has aged well because hallways spill nothing.

What we now ask for is partial fill: voids over roughly eight millimetres filled with a colour-matched cement rather than clear resin, everything smaller left open. The surface stays legible as stone, the texture survives, and the floor can be washed without ceremony. It costs more than either extreme because it is handwork, and it is the only version we would put in a house someone actually lives in.

Cutting for the threshold

The threshold is where stone projects are won or lost. It is the one piece everybody touches with their feet, every day, and it is the piece most likely to be cut on site by someone in a hurry.

Our rule is that thresholds are cut in the workshop, from the same block as the floor, and delivered numbered. A threshold cut on site from an offcut will be a slightly different colour and a noticeably different thickness, and the eye reads that seam immediately even when it cannot say why.

The second rule is a two-millimetre chamfer on every exposed arris. Not a bullnose, which looks municipal, and not a sharp arris, which chips within a year. Two millimetres, cut at forty-five degrees, hand-eased afterwards. It is invisible from standing height and it is the reason the stone still looks new after four winters.

What it costs to get it wrong

On our second travertine project the stone was ordered to a sample, not to a block. What arrived was two pallets from one bed and one pallet from another, and the difference was obvious the moment they were laid dry. We rejected the third pallet, waited five weeks, and the client paid for the delay in a rented flat.

Since then the sequence has been fixed: approve the block, photograph it with a scale, get the cutting plan back for signature, and lay the whole floor out dry before a single piece goes down in mortar. It adds two site visits. It has not gone wrong again.