What to check when buying granite by the square foot

How the square feet are counted

Granite is priced per square foot, and the first thing to understand is which square feet. A slab is measured in the yard, length by width, as it stands. That is the gross area and it is what you are charged for. The net usable area, what ends up on your counter or wall, is smaller: rough edges get trimmed, cut-outs come out of the middle, pieces are cut to length, and the blade takes a few millimetres at every cut. Expect gross to exceed net by ten to twenty per cent on an ordinary job and more on an awkward one.

Ask how the slab is measured. Some yards measure the full rectangle including irregular corners; others deduct. Both are fair if you know which before the bill arrives. Strips for sills, skirting and edging are often sold by the running foot; ask what width that assumes.

Thickness

A slab sold as 18 mm will measure a little either side of 18 mm across its face. That is sawing tolerance and is normal; the guide on slab thickness covers what each thickness is for. What you want to agree is a minimum. Carry a vernier, measure each slab at several points, and write the thinnest reading on it. A slab 2 mm under nominal across its whole face is a different, cheaper slab.

Cracks and fissures

A fissure is a natural line in the stone, formed as it cooled, that runs with the grain. It has no depth you can feel, no step across it, and the slab is as strong there as anywhere else. Many granites have them and they are not a defect.

A crack is a break. It may run across the grain, it is often straight, a fingernail catches on it, and when you tap the slab with a coin on either side of it the sound goes from a clear ring to a dull knock. A crack that goes through to the back is a slab that will break on the lorry or on the counter.

To check: wet the slab, look along it in raking light, run a fingernail across every line, tap around it, and look at the back at the same point. If you cannot tell, ask.

Resin fills and mesh backing

Many slabs are resin-treated at the factory. Epoxy is spread over the face, fills the natural pinholes and fissures, cures, and is polished off flush. This is normal, especially on figured, open-grained or softer stones. A dense black is often not resined because it does not need it.

Resin becomes a problem when it is doing structural work: a wide filled crack rather than a hairline; fill that is cloudy, soft or a different colour from the stone; fill that sits proud or has shrunk into a groove. Resin on a slab going outdoors or into a wet area will yellow and weather differently from the stone around it.

Fibreglass mesh glued to the back is the same story. It is routine on thin slabs, figured stones and anything fragile in transport and cutting; it is a problem when it is peeling, when the slab is going outdoors, or when a crack is visible on the face and the mesh is the only thing holding it. Ask why a slab is meshed. The answer should be about the stone, not about a repair.

Colour variation

Two slabs of the same name will differ. What you are checking is whether they differ within a lot more than you can live with. Stand the slabs together in daylight, wet them, and step back three or four metres. Look at them as a counter, not as a sample. Pick the slabs for the most visible run first and let the odd one out go under the hob.

Check the back

The back tells you things the face does not: deep saw marks where thickness has been lost, mesh, filled cracks ground off the face but visible from behind, damp patches where water has sat in a fissure. A painted or coated back is worth a question.

Wastage

Ten to twenty per cent over the net area is normal on a plain stone with a simple counter; L-shapes, islands, bookmatched walls and figured stones need more (see the guide on matching slabs from one lot). Order spares from the same lot at the same time. Breakage during cutting on site also comes out of your side.

Transport and loading

Slabs travel standing on edge, on an A-frame or leaning together with timber battens between, strapped tight, never flat. They are lifted with a crane, a forklift with a boom, or enough people, and they break when someone tries to flip one alone. Count and check each slab before loading and again at your end before the lorry leaves. Photograph the load. Agree in writing who carries the risk between the yard and your site, because a slab cracked on a bad road is a common cause of disputes.

What to agree in writing

Both sides should hold the same piece of paper. It should say: the stone name; the lot or block number and the slab numbers; the number of slabs; the size of each slab and the total area; how that area was measured; the nominal thickness and the agreed minimum; the finish; the grade, if the yard grades its stone; the price basis per square foot; who loads, who transports and who bears breakage; and the delivery date. A photo of the slabs with their numbers chalked on, attached to that paper, settles most disputes.

See the actual slabs

A sample tile is a different piece of stone from a different block. It tells you the species, not the shade, pattern or quality of what you will get. Come to the yard, see the slabs you are buying, wet them, measure them, tap them, and photograph them.