How to check an imported slab before you pay

Look at the slab wet, not only dry

Never judge a slab from one dry look. Splash water on the face, or ask for it to be wetted. Water brings the colour close to how it will look polished or sealed, and it brings out faint veining and cloudy patches that the eye misses on a dry surface. More useful still, water finds hairlines: a hairline crack absorbs water and shows as a dark line that stays damp after the rest of the slab has dried. Wet the slab, wait until it dries fully, and note any line that stays dark or any area that dries far faster than the rest. Ask what causes it before you decide anything.

Turn your attention to the back

After the face, ask to see the back of the slab. Many natural slabs, especially heavily veined stones and travertine, carry a fibreglass mesh bonded on with resin so the slab survives handling and cutting, and many have their face filled with resin to close natural pores and voids. This is ordinary industry practice and does not by itself mean a poor slab. It does mean the stone is more fragile or more porous, and that a large cut-out or a shaped edge may need care and support. What deserves a pause is a back covered in filled cracks and patches, or mesh hiding an old break. Ask what each repair is for.

Repaired cracks and filler

A repaired crack does not disappear; it changes appearance. Run a fingernail or a plastic edge across the face. Any change in texture, or a line that reflects light differently from the stone around it, points to filler or resin. Look again from a low angle towards the light: filler tends to be either shinier or duller than the stone, and it does not age at the same rate. A straight line that cuts across the veins rather than following them is usually a break, while a line that follows a vein may be natural to the stone. Tell the two apart, and ask where each one falls on your piece, since it may sit in an offcut.

Grading: why two slabs share a name

The trade describes stone by grade or selection: classic, extra, first selection and so on. These are commercial descriptions of how regular the pattern is, how clean the slab is and how few flaws it carries. They are not standard worldwide measures, and the definition shifts between suppliers and between blocks. So two slabs with the same name can differ in colour depth, vein density, staining and open veining. The name tells you the type of stone, not what your slab looks like. In practice: do not buy on a name or a photo from the internet. Pick the slab that will be cut for you, record its number, and do not accept a swap for another slab of the same name unseen.

Measure the thickness yourself

Nominal thickness is not an exact measurement. A slab described as two or three centimetres comes out with small variations, and the thickness can change from one end of the slab to the other after sawing and polishing. Take a tape and measure at four points at least, on different edges, not at one spot. Why it matters: thickness decides how the edge looks, and how strong the countertop is across a sink cut-out. It also matters because a price is normally worked out on one stated thickness, so two quotes on different thicknesses cannot be compared. Write down what you measured, and put it in the agreement with the edge profile you want.

Numbers: slabs from one block

Slabs sawn from one block are numbered in sequence, with the block number and slab number written on the edge or on a label. Consecutive slabs are as close as stone gets in colour and vein direction, and the further apart the numbers, the wider the difference. For vein matching, where two neighbouring slabs are opened like the pages of a book so the pattern mirrors, the slabs must be consecutive and laid the right way round. If your job needs more than one slab, ask whether the consecutive numbers can be set aside together, and photograph the numbers. Ask how the layout will be planned before cutting, because reordering slabs afterwards is all but impossible.

Check the polish at a low angle

Standing over a slab and looking straight down hides polishing faults. Crouch until your eye is near the level of the surface, put the lighting or the window on the far side, and look at the reflection of a long straight line on the face. If that reflection is wavy or broken, the surface is not flat. If you find dull patches inside a brighter shine, the polish is uneven or a local repair has been polished back in. Note too that some stones never reach a mirror shine by nature, which is a property of the stone rather than poor work. Check the whole slab, not just the middle; edges usually show it first.

Measure your piece from the usable area

The slab size written on the label is not the area you will get. Subtract the damaged strip along the edges, the cracks you would not accept on a visible piece, and the areas where the colour shifts sharply. Then see whether your piece still comes out whole from what is left. Take your longest piece, a kitchen run or a stair tread for example, and picture it on the slab with the vein running the way you want. Measuring on paper is not the same as measuring on the slab, especially with cut-outs, corners and long pieces. Ask how many slabs the job needs laid out this way, and ask for the cutting plan before you pay, not after.

Photograph the slab with its number, and put the agreement in writing

Before anything is cut, photograph the whole slab with the block number and slab number in the same frame, and photograph any repaired crack or area of different colour. Those photos are your reference if something changes later. Then write the agreement down: which slabs by number, the finish, the thickness, the edge profile, who does the cutting and the cut-outs, and when the site measurements are taken. An agreement written on WhatsApp is enough and saves an argument after installation. Keep the messages and photos together in one place until the job is finished. If you want our opinion on a slab before you pay, send us the photos on WhatsApp.