How to check natural stone quality

When your stone is made in another country, checking quality is how you protect your money. Here is what to measure on every lot, which lab tests to ask for and how video inspection helps.

Check every lot

1. Size and thickness

Agree the size and thickness tolerance in writing before you order. When the goods arrive, or on video before dispatch, measure about ten slabs from each pack with a tape and a calliper. Compare them with the agreed tolerance.

2. Squareness and edges

Measure both diagonals of a slab. They should match. Sawn edges should be clean, straight and free of chips.

3. Surface and flatness

Lay a straight edge across sawn slabs to check flatness. On natural split slabs, the surface will be uneven by nature, but should not rock on a flat floor.

4. Colour range

Compare the lot with your approved sample. Natural stone varies, so look for the spread of colours across several packs rather than expecting a single shade.

5. Defects

Look for cracks, hairline fractures, clay or iron veins, soft or crumbly patches and chipped corners. A simple tap test helps. A sound slab rings. A cracked one sounds dull.

6. Packing

Check that packs are crated or strapped, corners are protected, packs are counted and labelled, and the container load is photographed before it is sealed.

Lab tests to ask for

Importers in the UK and Ireland often ask for a test report for each stone. Common ones are:

Ask for the report for the exact stone and finish you are buying. A report for a different stone does not cover your order.

Checking from a distance

We inspect every lot and film every lot and every pack, then share the videos before dispatch. To get the most from a video, ask for specific things:

• A wide shot of each pack, with the pack number visible.
• Five slabs from each pack measured on camera.
• Close-ups of corners and edges.
• The spread of colour when slabs are laid side by side.
• The container being loaded.

You can also hire an independent inspection company, such as SGS, Bureau Veritas or Intertek, to check the lot before it ships.

Keep a reference sample

Sign off a sample before the order and keep it. On arrival, photograph the pack labels and compare the delivery with the sample. Report any damage to your supplier and carrier within the time set in your terms.