Selecting the Stone

Portland Stone Selection and Assessment

Portland Stone has been used as a building material for centuries, and many historic buildings stand as a testament to its strength and durability.

As outlined in Stone Federation guidance and relevant British Standards, understanding the geological variations of Portland Stone is essential. These variations can influence the stone’s character, selection, cost, programme, and overall project design.

Pre-Tender Stone Selection

At the pre-tender stage, a shortlist of stones should be researched to ensure:

• Geological features are clearly understood and documented.
• Adequate block quantities are available to accommodate manufacturing wastage and meet the construction programme.
• The largest and frequently occurring units can be produced from available blocks.
• Technical data is available for cladding design, and a Declaration of Performance (DoP) can be issued upon order placement. Initial Testing and Production Control Testing (PCT) may be required for stones with limited local use, or where technical data or DoPs are incomplete or outdated.
• The required surface finish is clearly defined.

Samples and Reference Panels

Indicative Stone Samples

• Small samples that show typical colour and texture.
• Cannot fully represent the natural variations inherent in all stones.

Range Panels

• Display the typical geological characteristics of different beds of Portland Stone.
• Once approved, indicative sample panels can be supplied to the project site, showcasing a selection of stones from the Albion Stone range. The original reference panels are retained at the Portland factory, which will serve as the control for manufacture.
• Excluding some geological features from approved samples will have a cost, programme, and sustainability implications. The stones included in the range panels have already undergone rigorous selection, so any further selection should be avoided wherever possible.

Assessment of the Stone

Inspection of Existing Buildings

Albion Stone can provide a list of local buildings constructed using their stone for reference. Our Business Development Manager, Ben Levy, will also host tours around London, where we can showcase a variety of Portland Stone buildings we have completed over the years. Observations will include:

• Close-up inspection of texture, shell distribution, and note that stone will case-harden over time, forming a protective surface that can obscure shell features.
• Distant inspection to assess geological characteristics visible from afar.

Inspection of the Mine and Factory

• Early visits allow designers to evaluate production capacity, stock quantities, block sizes, quality systems, and environmental performance.
• Externally verified certificates can also be reviewed during these visits.

Mine Report

• Albion Stone produces a quarterly Mine Report detailing current and future stone availability, typical and maximum block sizes, and other relevant production information.
• Visits to the mine are encouraged to review Range Panels, examine mine faces, and consult with production teams.

To see our latest Mine Report, please view our News Page

Technical Data and Testing

• All Albion Stone technical data aligns with BS 8298 part 2, Section 4.2.4, drawing on over 12,000 tests conducted over 30 years.
• This data informs CE (UKCA) certificates and DoPs.

Production Control Testing (PCT)

• Stones are tested to the minimum level required by relevant standards.
• More frequent testing may occur if geological properties show variation.

Initial Testing and Project Specific PCT

• Usually required only in exceptional circumstances.
• Stones with limited local use or inadequate technical data will need Initial Testing and a project-specific PCT programme per BS 8298 Part 2 section 4.2.6
• Sample plans and reports should follow BS 8298 part 2 Section 4.2.7 to ensure representative geological features are tested.
• These processes can impact project costs and programme.

The Stone Federation have prepared an online CPD on Selecting the Correct Stone.