Millstone Grit (West Yorkshire) – Sawn Yorkstone
Yorkshire “banded” gritstone
This Yorkstone is a sedimentary sandstone formed over 300 million years ago in the Carboniferous period as silt deposited by rivers and consists of quartz, mica, feldspar, silica, clay and iron oxides visible in the bind.
First quarried in Yorkshire during medieval times by the 18th century a large industry developed quarrying the yorkstone of the millstone grit and coal measures in West Yorkshire.
The first quarries or ‘delves’ were developed in the outcrop on the valley sides and later began to move underground into large chambers or galleries. Deep yorkstone quarries and mines became possible after the introduction of gins and steam cranes and the earliest shafts were sunk in Hipperholme, close to Halifax in about 1860.
This is a hard Yorkstone from the millstone grit of the carboniferous age. It is a tightly banded and hard fine to medium grained stone which is fawn in colour with some brown veining.
Safety in use Slip Resistance (note 1)73 Wet. Values >40 are considered safe Abrasion Not testedValues < 23.0 are considered suitable for use in heavily trafficked areas Resistance (note 1) Strength Under Load 1) Compression (note 2)123.7 MPaLoaded perpendicular to the bedding plane ambient humidity 2) Bending (note 1) 13.7 MPa Loaded perpendicular to the bedding plane ambient humidity 12.6 MPa Loaded perpendicular to the bedding plane ambient humidity Porosity and Water Absorption 1) Porosity (note 3) 11.5% 2) Saturation Coefficient (note 2)0.66 3) Water Absorption 3.2% (by wt) 4) Bulk Specific Gravity 2371 kg/m3 Resistance to Frost Flexural strength after Freeze/ thaw test (note 1) 13.0 MPa Loaded perpendicular to the bedding plane ambient humidity Resistance to Salt Sodium Sulphate Crystallisation Test (note 3) -1.13%Mean wt loss Sodium Sulphate Crystallisation Test (note 3) (saturated) 51% Mean wt loss Resistance to Acidity Acid immersion (note 4)Pass (test methods Note 1 = prEn1341, Note 2 = PrEN 1342, Note 3 = PrEN 1341 / BRE 141, Note 4 = BRE 141) Sample Number J99/0557 Test Salt Crystallisation Mean Value -1.1 Percentage mass change EXPECTED DURABILITY AND PERFORMANCE It is important that the results from the individual test are not viewed in isolation. They should be considered together and compared to the performance of the stone in existing buildings and other uses. Sandstone is traditionally acknowledged as generally being a very durable building and paving stone and has been used extensively in many towns and cities in the UK. A durable stone that will have good resistance to acid rain or air pollution. In addition the negligible weight loss in the sodium sulphate crystallisation test indicates good resistance to salt damage under normal conditions. The higher weight loss on the harsher saturated sodium sulphate crystallisation test indicates that some care is required in more aggressive conditions (for example in coastal locations or from de-icing salts). From the frost test the stone should also have good frost resistance. The compressive and flexural strength of the stone is midrange for a sandstone and is comparable with many sandstones. The density and compressive strength indicates that the stone should be suitable for use in moderate to heavily trafficked areas. The stone should be suitable for use in most aspects of construction including flooring, paving load bearing masonry and cladding. Special consideration is required for areas where a long service life is needed in harsh salty environments. This data sheet was compiled by the Building Research Establishment (BRE)> it is base on data from the current tests at BRE (2000). The data sheet was compiled in May 2000. The work was carried out by BRE as part of a Partners in Technology Programme funded by the Department of the Environment. Transport and the Regions and George Graham Sons & Ci, and does not represent an endorsement of the stone by BRE.
