Selecting the Stone
Portland Stone has been used for centuries as a building material and these buildings stand as testaments to the stone’s strength and durability.
As stated in the Stone Federation guidance and relevant British Standards, it is vital to understand the geological variations that make up the typical character and any selection implications on the costings, programme and design of the natural stones that are proposed for the project.
At the pre-tender stage of the project a shortlist of stones should be researched to ensure that
·the geological features are clearly understood and documented
·adequate quantities of block are available allowing for manufacturing wastage, to meet the construction programme
·the largest and frequently occurring units can be readily produced from the blocks available
·the technical data is available to allow the design of the cladding and a Declaration of Performance (DoP) is available on placement of the order. A programme of Initial Testing and Production Control Testing may be required for stone with limited use in the local area or where the technical data and DoP is inadequate, out of date or incomplete.
·the surface finish required has been established
The initial selection for a short list of stones to be used on the project should be made from Indicative Samples. The range panels (reference samples) held at Portland, show the designer the typical geological characteristics in each bed of Portland Stone.
These are small samples that show the typical colour and texture but cannot show the natural variations that are present in all stones.
The range panels are designed to show the typical geological characteristics present in the different beds of Portland Stone. Once approved, a duplicate set can be prepared for the project site, but the original needs to be retained at the Portland Factory for reference during the manufacture of this and other projects.
There are likely to be cost and even programme and sustainability implications if the approved reference samples exclude some geological characteristics typically found in the stone.
Assessment of the stone
Inspection of existing Buildings
Albion Stone can provide a list of local building constructed using our stones that can be viewed.
·First view at close proximity noting the texture and shells and their distribution. Do note, that the stone will case harden over time and this process forms a protective coat over the surface that tends to dull and disguise the natural shell structures.
·Then view the stones from a distance noting the geological characteristics still visible.
Inspection of the mine and factory
A visit to the mine should be arranged early in the stone selection process to give the designer the opportunity to look at the production capacity, the stock quantities and typical sizes of the blocks and to compare these with the project’s requirements. The actual quality systems and environmental performance can be assessed as well as the externally verified certificates during this inspection.
To ensure our customers have all the information available to make an informed decision about the stone, Albion Stone prepare a quarterly Mine Report which details the current and future availability of a particular bed of stone, together with information about the typical and maximum block sizes. We also welcome visits to the mine to view the Range Panels and to examine the mine faces and talk to our production teams about the project. To see our latest Mine Report, please view our News Page
As recommended in the industries technical publications such as BS 8298 part 2, Section 4.2.4 all Albion Stone’s technical data contains current and historical data, which is from over 6,000 tests completed over 30 years by the leading laboratories. This technical data is used to prepare the CE (UKCA) certificates and DoPs.
Production Control Testing (PCT)
As part of our PCT we test all our stones to the minimal level required by the relevant product standards, but in many circumstances will be tested on a more regular basis if we notice a slight change in the stone’s geological properties.
Initial Testing and specific PCT for a Project
Our stone will only require project Initial Testing and specific PCT in very exceptional circumstances. Other stones that do not have a history of use in the local area and/or the proposed application, will probably require Initial testing to be completed, particularly where technical data is inadequate, and a programme of Project PCT as stated in BS 8298 Part 2 section 4.2.6. should be completed. This will have an impact on the projects programme and costs. A Sample Plan and sample Report for the selection of the samples for testing should be prepared in accordance with section 4.2.7. in BS 8298 part 2 to ensure that representative samples of the geology are tested.
The Stone Federation have prepared an online CPD on Selecting the Correct Stone.
Albion Stone, a fourth generation family business pride ourselves on having a helpful and skilled workforce as well as modern and traditional manufacturing process to enable us to produce the highest quality Portland Stone with minimal environmental impact.
