Sourcing Traditional Materials
Conservation guidelines stress the importance of using original materials for repair: their behaviour has been well established over centuries of use, they interact well with the original materials, and they preserve the special character of the historic building or structure. Unfortunately many traditional materials are now difficult to source, and their correct preparation is sometimes poorly understood.
Historic England is researching the special characteristics of various traditional materials, and finding ways of making them more readily available for building conservation.
We are currently working on three projects in this area, covering:
- Strategic Stone Study
- Sourcing Collyweston Slates
- Sourcing thatch
Strategic Stone Study
In historic buildings conservation work it is vital to obtain stone, which matches the original in its mineral composition, density and porosity. If not, new stone could hasten the decay of the original and is unlikely to weather in the same way, therefore looking very different.
To get a proper match, new replacement stone has to come either from the original quarry or at least from one in close proximity to the original supply.
The rich diversity of England’s geology means that hundreds of different stone types have been used over the centuries for building purposes. However accurate information on the original quarries and the number and distribution of the buildings constructed from those stones is very scant.
The Strategic Stone Study aims to address these problems by comprehensively mapping all the active, dormant and historic quarries within England, identifying the building stones they provided and matching them to buildings and structures.
Historic England is working with the British Geological Survey, local geologists and historic buildings experts from each county in England to identify the most important building stones used and representative buildings and the location of quarries.
Sourcing Collyweston slates
Until recently there were no sources of new Collyweston slates which had been used historically throughout the East Midlands. Nearly all the material used for repair and conservation was reclaimed from other buildings, which is not sustainable in the long-term.
Following research at Sheffield Hallam University to develop an artificial frosting process and large scale trials by Historic England at Apethorpe Hall in Northamptonshire an artificial frosting process for the production of Collyweston slate has now been established.
This system has now been taken up by two companies and reliable, year-round production of the slates is possible for the first time in many decades and is no longer dependent on unreliable winter frosts.
Concern over a sufficient and suitable supply of thatching straw has been an issue for many years. The National Thatching Straw Growers Association is being funded to grow and monitor the performance of older 19th century varieties of wheat, which were known to have produced better thatch and be more resistant to bad weather.
The project consists of two complementary and linked work packages. In the first package growth trials of five wheat varieties were carried out to monitor and evaluate the growing, husbandry and harvesting of the cereal crops, including the use of different fertilisers. You can read the resulting report on the initial thatching straw growing trials.
This is being followed by thatching small roof frames for long term annual monitoring of completed thatch with different types of thatching to assess the effect of treatment on longevity.