The BRE / British Stone Stone List
Full project details
Technical Data Sheet
Portland Cap Limestone
Bowers Quarry, Isle of Portland
Contact : Albion Stone Quarries Ltd
Tel. 01737 771
772 Fax. 01737 771 776
email: sales@albionstonequarries.com
website : www.albionstonequarries.com
Grid Reference: SY 696 730
Compiled September 1997
This data sheet was compiled by the Building Research Establishment (BRE). Where possible, data collected in earlier surveys has been used to help interpret the test results. The data sheet was compiled in September 1997 using the results of tests carried out to the proposed European Standards. 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 Albion Stone Quarries Ltd and does not represent an endorsement of the stone by BRE.
General
The quarry is situated off Wide Street in Easton on the Isle
of Portland. The quarry also produces Whit Bed, Base Bed and Hard Blue
Petrography
The stone is an creamy-white limestone which ranges from fine
grained to open textured. It is an oolitic limestone from the Portlandian
formation (Jurassic). The stone is formed from ooliths in a micrite (fine
grained calcium carbonate) matrix.
Expected Durability
and Performance
It is important that the results from the sodium sulphate crystallisation
tests are not viewed in isolation. They should be considered with the results
from the porosity and water absorption tests and the performance of the stone in
existing buildings. Stone from the Portland Cap Bed is a very new product to the
building industry but the results and its record of use in sea defences suggest
it is very durable and is comparable with Whitbed. It is difficult to compare
the results for the Cap Stone from Bowers Quarry to those collected from
buildings and exposure trials as the stone has not been used in building
construction. However, the overall test results suggest that the stone is strong
and of good durability. The crystallisation test results show the stone to be
Class A which BRE Report 141 suggests that it is suitable for all uses. The
abrasion results indicate that the stone would be hard wearing even in heavily
trafficked areas. Previous research at BRE has shown that Portland limestone which has a low
saturation coefficient (<0.72), a low microporosity (<11.0 of the stone by
volume) and an open oolitic structure generally performs well over long periods
when used on buildings. The results summarised on these sheets show that most of
the samples tested meet these criteria. In all cases it is important that the detailing of the stonework is designed
to offer the maximum protection from rainwater and rainwater runoff. Based on
current research it seems likely that the stone would weather at a rate
of between 1 and 2 mm per 100 years but it could be greater in severe exposures.
(Test methods Note 1 = prEn1341, Note 2 = prEN 1342, Note 3 = prEn 1341 /BRE 141, Note 4 = BRE 141)
All tests were carried out at BRE in July 1996)