Ten common stone specification mistakes, and the wording that prevents them

At a glance

Read 7 Nov 2026: Stone Federation GB guide SS 01 (2010) and BSI listings. The standards were not read, so no tolerance or strength figure is given. Practice points are in the unverified list.

Ten gaps, marked on a floor

A stone specification fails in a predictable way: it leaves a gap, and a tenderer fills that gap with the cheaper answer. The ten mistakes below are the gaps we see most often in how stone is written up. Each has a consequence and a fix that goes into the clause. The numbered drawing marks where each one sits on a section through a floor.

The first six are about what is being bought: the stone, the finish, the size and the evidence. The last four are about where it goes and how it is looked after. None of this is design advice. It is a way of making the written specification say what the designer means.

Mistakes 1 to 3: naming the stone and its finish

1. Trade name only. A commercial name can cover several stones, and some stones have more than one commercial name. The Stone Federation guide says samples should be labelled to BS EN 12440 with the traditional name, quarry location and country of origin, the petrological family and a sample reference number, and that if a supplier cannot or will not give that information, an alternative stone should be chosen. Write the petrographic name (BS EN 12407 describes the examination), the denomination to BS EN 12440, the origin, and the sample number.

2. No range panel. A single sample cannot show natural variation. The Stone Federation guide separates an indicative sample, typically small (about 150 x 150 mm), from range or control samples: about ten large stones, at least 600 x 400 mm or the project’s common sizes, showing the typical variation in colour, texture, veining and the rest, with any fills declared, selected by the quarry or mine. It adds that rejecting characteristics typical of the stone can mean abortive cutting, prolonged procurement and increased costs. Name the range panels as the control samples, and agree what counts as typical before cutting starts. See the sample, slab and book-match sheet.

3. Finish not defined. The guide says samples should be marked with the surface finish and, for a honed or fine-rubbed surface, the grit used, so the specifier can specify the finish accurately. Write the finish by reference to the approved sample, and state it on the schedule. See natural stone finishes.

Mistakes 4 to 6: size, evidence and slip

4. Size without thickness. A stone format is meaningless without a thickness, and the right thickness depends on the stone, the format, the base and the use. The slab standard, BS EN 12058:2015 (floors and stairs), carries thickness tolerances that changed in the 2015 edition; we have not read the values. Put the face size, thickness and tolerance on the drawing, and ask the stone workshop to confirm in writing that the thickness suits the stone, the format, the base and the use. One UK supplier’s manual treats 20 mm as suitable for its own stone in certain formats: that is a data point for one stone, not a rule. See natural stone flooring specification.

5. No test data asked for. Stone is a natural product, so ask for the evidence: declared flexural strength (BS EN 13161), apparent density (BS EN 1936), slip resistance (BS EN 14231) and, where relevant, abrasion (BS EN 14157), together with the declaration of performance for the product standard. Name each test method, and require the data before order.

6. Slip not stated. A polished stone can be slippery when wet, and the finish changes the answer. BS EN 14231:2003, listed by BSI as current and under review, describes a pendulum test for natural stone floors. BS 7976, which many specifications still cite for pendulum testing, was withdrawn in 2022 and replaced by BS EN 16165:2021. State the test, the surface (as finished), wet, and the slider. Do not invent a target value: see the slip resistance sheet for how HSE reads the result.

Mistakes 7 to 10: exposure, base, joints and care

7. Acid and stain exposure ignored. Marble and limestone are attacked by acids, and porous stones stain. A bar, a kitchen or a spa puts them in the way of both. The fix is in the brief, not the sealer: state the exposure, choose stone and finish to match it, and say what the sealer is for and what it cannot do. See the sealing, staining and etching sheet.

8. Heating and base ignored. Underfloor heating, the screed, its moisture and its flatness are part of the stone specification. State them, require the base to be accepted in writing before laying, and require any heating to be commissioned first. Cite BS 5385-3:2024 for installation: BS 5385-5:2009, still named in many older specifications, was withdrawn on 30 May 2024. See underfloor heating.

9. Movement joints not set out. Joints that appear only on site appear in the wrong place. Put them on a stone layout drawing, approved before fabrication, at the perimeter and over every movement joint in the base, through the full depth. See floor transitions and movement joints.

10. Protection and care not specified. Many stone floors are damaged after laying, by following trades. Specify protection to handover, the sealer and the cleaner, and a care document at handover. See the handover and O&M pack sheet for how handover papers are organised.

From a vague line to a clause

The drawing below shows the idea: a vague line, and the same line with its parameters fixed. The wording at the foot of the page puts it into a clause you can paste. It is in our own words, with values in square brackets, and its structure follows the way specification clauses for natural stone are usually organised (stone, finish, size, evidence, installation).

Cost drivers, in words, not prices. As at 7 November 2026, and from practice rather than from a document we read: larger formats, thicker slabs, tighter selection (less of each block is usable), more demanding finishes and higher wastage all tend to push the price up. The Stone Federation guide says rejecting typical characteristics can cause abortive cutting and higher costs. A specification that fixes the parameters stops a tender from competing on a cheaper stone. It does not make the stone cheaper. Ask the stone partner for the effect of each on your project.

Natural stone [floor slabs to BS EN 12058 / modular tiles to BS EN 12057, confirm current edition]. Petrographic name to BS EN 12407: [ ]. Denomination to BS EN 12440: [ ], quarry or mine [ ], country [ ]. Reference sample [no.]. Finish [honed] to approved sample [no.], grit [ ]. Range panels [ref] are the control samples for the whole run; fills, if any, are declared and shown on them.

Face size [ ] x [ ] mm, thickness [ ] mm, tolerances as the product standard [confirm current edition], to drawing [ref]. The stone workshop confirms in writing that the thickness suits the stone, format, base and use. Before order the supplier provides the declaration of performance and test results for flexural strength (BS EN 13161), apparent density (BS EN 1936) [and abrasion (BS EN 14157)].

Slip resistance measured by the pendulum test on the finished surface, wet, with [Slider 55 or 96], to [BS EN 16165 Annex C / BS EN 14231, confirm current edition]. The designer states the value required: [ ]. The report is supplied before order, and again from a sample of the finished floor.

Exposure: [bar / kitchen / spa / entrance] with [acids, oils, salts]. Sealer: [type, for purpose X] by the stone fixer; cleaner [pH-neutral]. Base [screed] [ ] mm, accepted in writing as flat, dry and cured before laying; heating commissioned and tested before laying. Installation to BS 5385-3:2024 [confirm current edition]. Movement joints as stone layout drawing [ref], approved before fabrication. Floor protected with [board] until handover. Care document at handover.

Standards and sources

• Stone Federation GB, Selecting the Correct Stone (SS 01): April 2010, footers Feb 2011. Read 7 Nov 2026.
• BS EN 14231:2003: BSI listing seen 7 Nov 2026: Current, under review. Text not read.
• BS EN 12058:2015, 12057:2015, 12407:2019, 12440:2017: current per the library notes of 5 Nov 2026. Texts not read.
• BS 5385-3:2024: current; replaces BS 5385-5:2009, withdrawn 30 May 2024 (library notes). Text not read.
• BS EN 13161, 14157, 1936; BS EN 16165:2021: 13161:2008 and 14157:2017 seen only on retailer listings; 1936 not checked; 16165 per the slip sheet. Confirm.

Questions we are asked

What is the most common stone specification mistake?

Naming a stone by trade name alone. Several stones can sell under one name, so a tenderer can price a cheaper one. Name the stone by its petrographic name, denomination, origin and a sample reference.

Do I need to specify the thickness of a stone floor?

Yes. A size means little without a thickness, and the right thickness depends on the stone, the format, the base and the use. Put it on the drawing, with tolerances, and ask the workshop to confirm in writing that it suits.

What is a range panel?

A set of large stones from the quarry or mine, chosen to show the typical natural variation in the stone, agreed in advance. It is the control sample the delivered stone is compared with.

Is BS 5385-5 still the standard for stone floors?

No. BSI lists BS 5385-5:2009 as withdrawn on 30 May 2024. BS 5385-3:2024 now covers floors. Check the current edition when you write the clause.

What slip resistance should I specify?

We do not give a target. State the method, the surface as finished, wet, and the slider, and set the value required with the designer and the duty holder. See the slip resistance sheet for how HSE reads the result.

Can a specification make the stone cheaper?

No. It stops a tender competing on a cheaper stone, finish or thickness. Cost drivers include format, thickness, finish and selection yield: ask the stone partner for the effect on your project.