Stone sample, slab and book-match approval: variation, range panels and substitution

At a glance

Sizes and wording are Stone Federation GB's (SS 01, 2010; snagging guide, August 2022) for larger projects. Step 5 is common practice. General industry practice, not a studio service.

One approval path, seven steps

Natural stone cannot be approved from one small piece. A sample shows what the stone can look like, a range shows what it will look like across the job, and a slab selection shows which pieces you are getting. The sheet puts them in one path, so that each step approves one thing and leaves the next open.

Seven steps follow. The solid boxes are described in one of the two Stone Federation Great Britain documents read for this sheet (Selecting the Correct Stone, SS 01, 2010, and Inspection and Snagging of Finished Internal Works Using Natural Stone, August 2022). The dashed boxes are common practice that we could not find in a document: the stone workshop confirms its own process, and the master drawings say which leaf goes where.

This is general industry practice for stone on larger flooring, cladding and paving projects, not a description of what any supplier provides. What is made, by whom, and when is agreed for each commission.

Samples: label them and say what each proves

Label every sample. Stone Federation GB asks that all samples are labelled to BS EN 12440 (denomination criteria): the traditional name, the quarry location and country of origin, the petrological family and a sample reference, so the stone can be compared with earlier samples and with buildings that use it. If a supplier will not give that information, the Federation advises choosing another stone. Mark the surface finish on the sample too, with the grit size for a honed or fine rubbed finish, so the finish can be specified exactly.

An indicative sample shows general colour, tone and texture, and ‘cannot and should not attempt to show’ the range of geological characteristics present in all stones. The Federation gives about 150 x 150 mm as the typical size, small enough to post round a project team, and says a short list is usually made from them. One UK stone supplier's specification clause says the same thing in its own words: the indicative sample reference shows the surface finish but not the full extent of the visual range.

Range or control samples are prepared for the project, or are panels of current production already held at the quarry or mine, showing the typical range of features in the bed of stone. The Federation says normally about 10 large stones of at least 600 x 400 mm, or the sizes of the common stones on the project, with the typical variations in colour, texture, veining, shell content, grain size, and the distribution, character and frequency of each. If the processing involves patching, fillers or resin for natural holes, faults or cracks, the processor declares it and the range samples include it. Selecting a suitable number of samples from various blocks of the chosen bed is the quarry or mine's responsibility, ideally at the extraction site. Everyone then views the range and agrees an acceptable range for the project.

Viewing. The Federation says stone samples are viewed from at least 2 m, in the orientation in which the stone will be used, in daylight for external work and in light like the project's for internal work. It gives this as what BS EN 12057, 12058 and 1469 state; we have not read those standards. In a small room where 2 m is not possible, the Federation's guidance for installed stone is to view from the centre of the room but no closer than 1 m, in daylight with wall lights and downlighters off, not with torches or site lights.

Take photographs. The Federation's web page on sample panels says to take high-resolution photographs of the final selection for future reference. For a fault, the snagging guide asks for a photograph at 1 x magnification with a scale-rule, pen or coin beside it, and enhanced magnification only in addition to that.

Natural variation: write the range down

The aim of the range is to stop two people disagreeing about the same stone after it has been cut. Stone Federation GB says that variation is part of the material's character and that, unless the acceptable range is agreed early, it can be a cause of tension between the quarry and the architect. Rejecting features that are normal for the bed leads to abortive cutting, longer procurement and higher cost, and the Federation says all characteristics accepted in the range samples are to be treated as typical of normal production and not as flaws, unless their concentration becomes excessive and the typical character of the stone is lost.

For installed internal work the August 2022 snagging guide goes further. It says all visible natural features, including vents, cracks, inclusions, cavities, stylolites and veins, are permitted as far as they are typical for the stone and its performance is not adversely affected, and that they should be identified and agreed before purchase and recorded in a project-specific range report. That is a document, often required in the contract specification, where an independent stone consultant sets out the expected appearance of the stone with every acceptable and rejected feature. The report is then the benchmark for the material and its appearance, including factory fills and natural veining. The guide says the report is too often discarded at the installation stage, so snagging becomes a matter of one person's opinion, and asks for the same people to carry on from selection to inspection.

No colour tolerance. We found no document that gives a numerical tolerance for the colour or veining of natural stone, and this sheet gives none. BSI's scope for BS EN 12057:2015 lists geometrical, physical and mechanical characteristics, and BS EN 12058:2015 changed its nominal thickness tolerances (its figures were not read). Beyond the Federation's statement about viewing samples, we cannot say what the standards say about appearance. The Federation's answer is a range sample and a range report, and the specification wording below follows it.

Slabs and book-matching: draw it, number it

A slab is a large flat piece of stone, sawn from a block. Slabs from one block, cut one after the other, are close to each other in colour and vein pattern, and the order they were cut in is what makes a match possible. Our veneer and book-matching article describes the same idea for consecutive veneer leaves; a stone merchant's own page describes stone the same way: slabs cut from one block and laid side by side in sequence. We found no standard or trade-body definition of the match names, so the drawing below is how this sheet uses them. Define the words you use on your own drawing.

• Book match. Two consecutive leaves are opened like the pages of a book, so the pattern mirrors about the joint. Veins that run to the joint meet in a shape that is symmetrical about it.
• Slip match. Consecutive leaves are laid side by side in the same orientation, so the pattern repeats and steps at the joint. The veins do not meet across it.
• Four-way match (quarter match, diamond match). Four leaves are mirrored both ways about a centre point, so the pattern runs in to or out from the centre. Two pairs of consecutive leaves are needed, one of each mirrored on the other.

What the drawing must say. Say which match, name the block and number the leaves in the order they were cut, show the position of every leaf and which way its veins run, and mark the joint positions and widths. A mirror is close but not exact: ask for the main vein to meet at the joint within a stated figure, and agree that figure on a dry lay, not for perfect symmetry. A matched set is also a set, so if one leaf is damaged the next leaf in the sequence is not a match for its neighbour. Agree beforehand how a replacement will be found (an unused leaf from the same block, or a new layout shown for approval).

Substitution and change control

Substitution control is the other half of approval. The risk is not that a lot is bad but that it is a different lot: another bed, another block, another finish line or another processor, which no longer matches what was approved. The wording asks for four things.

Ask for a Declaration of Performance and the denomination to BS EN 12440 for each delivery, so the paperwork identifies the stone you approved. How CE and UKCA marking apply to natural stone in Great Britain now was not checked for this sheet: the snagging guide mentions a review of the Declaration of Performance and UK CA marking information, and the stone workshop should confirm what it supplies. For the general rule that a change after approval is a new sample, see sample hierarchy and approval, and for a register of changes substitution and value-engineering register.

Common mistake: approving the stone from a small indicative sample and the price from a slab photograph. The first shows none of the variation and the second shows one slab; neither is the benchmark the delivered stone will be judged against.

Stone: [traditional name], petrographic name to BS EN 12407 [ ], denomination to BS EN 12440 [ ], quarry or mine [ ], bed [ ], country [ ]. Finish [honed, grit [ ]]. Indicative sample [ref], [about 150 x 150] mm, labelled with traditional name, quarry location, country of origin, petrological family, sample reference and finish, is approved for general colour, tone and texture only.

Range or control samples [ref]: [about 10] stones not smaller than [600 x 400] mm, or the sizes of the common stones on the project, selected by [the quarry or mine / the stone consultant] from blocks of the chosen bed, showing the typical variation in colour, texture, veining, [shell content, grain size] and any fills, held at [location]. A range report by [independent stone consultant] lists the features accepted and rejected and is the benchmark for the delivered and the installed stone. Features within the range are not defects unless their concentration becomes excessive and the typical character of the stone is lost. Fills are declared by the processor and included in the range samples.

Slabs for [areas] are selected by [designer] at [the quarry / processing works] on [date], in [daylight / light like the project's], photographed at 1:1 with a scale, and numbered in the order cut from block [ref]. Match: [book / slip / four-way] as layout drawing [ref], which shows the block, the leaf numbers, the direction of the veins and the joint positions and widths. Main veins to meet at joints within [ ] mm, as agreed on dry lay [ref]. Unused leaves from the same block are reserved for replacement until [handover]. Before delivery the stone is dry laid at the works and inspected against the drawing and the range report, viewed from [2] m in light like the project's (from the centre of a small room, no closer than [1] m), by the people who approved the samples; faults are photographed at 1:1 with a scale.

No change of stone, quarry, bed, block, finish, thickness or processor without the designer's written approval. A different block or finish is submitted against the range report as a new sample. Each delivery carries a Declaration of Performance and the denomination to BS EN 12440 for the stone supplied, matching the approved sample [ref].

Standards and sources

• Stone Federation GB, Selecting the Correct Stone (SS 01, April 2010): read in full; lists BS 5385-5, withdrawn 30 May 2024.
• Stone Federation GB, Inspection and snagging of finished internal works using natural stone (Aug 2022): read in full.
• Federation sample-panels page; Designing Buildings wiki; Stone Specialist column: read via a fetch summary.
• BS EN 12440:2017, 12407:2019, 12670:2019, 12058:2015, 12057:2015: BSI listings read, all current; texts not read.

Questions we are asked

What is the difference between an indicative sample and a range sample?

An indicative sample, typically about 150 x 150 mm, shows the general colour, tone and texture and cannot show the range of geological features. Range or control samples show that range: Stone Federation GB says normally about 10 large stones of at least 600 x 400 mm, or the common project sizes, with the typical variation in colour, texture, veining, grain size and fills.

How many samples does natural stone need?

There is no single number. The Federation's guide for larger projects gives about 10 large stones for the range, chosen by the quarry or mine from various blocks of the chosen bed. For a small interior order the stone workshop will say what it supplies; the principle is a range, not a point, and a written range report as the benchmark.

Can I specify a colour tolerance for natural stone?

We found no document that gives a numerical one. The Federation's approach is to agree a range sample and write it down in a range report, so that features within the range are accepted as typical of the stone and not treated as flaws, unless their concentration becomes excessive.

What is book matching, and how does it differ from slip matching?

In a book match, two consecutive leaves cut from one block are opened like the pages of a book, so the pattern mirrors about the joint. In a slip match, consecutive leaves are laid side by side in the same orientation, so the pattern repeats and steps at the joint. A four-way match mirrors four leaves about a centre point. Names vary between trades, so define them on the drawing.

Do I need to visit the quarry?

The Federation strongly advises a visit to the quarry or mine and the processing works, ideally with an independent stone consultant or geologist, particularly for a stone you do not know. The range samples are normally inspected on the visit, and the final selection is photographed for the record.

How do I stop a different lot of stone arriving?

Name the stone to BS EN 12440, approve a range report, number the slabs in sequence on the layout, ask for a Declaration of Performance with every delivery, and write that any change of quarry, bed, block, finish, thickness or processor needs written approval and a new sample against the range report.

From how far should stone be judged?

The Federation says samples are viewed from at least 2 m, in the orientation of use and in light like the project's, and gives this as what BS EN 12057, 12058 and 1469 state. In a small room where that is not possible, installed stone is viewed from the centre of the room, no closer than 1 m, in daylight with the lights off.