OBTAINING STONE FOR ROOF CONSERVATION

“Can’t they find a quarry somewhere more suitable, like an industrial estate in the Midlands?” This suggestion was made by an objector to a proposal to re-open a quarry which had supplied the raw materials for hundreds of historic buildings in the south west and for which no other source was available.  These sentiments are regularly expressed whenever a quarry is proposed, regardless of its size, purpose or intended duration.  Clearly the notion that any similar stone will do instead is not one that accords with those who are trying to conserve historic buildings.

Why is it so important to use the correct stone?  Building owners and English Heritage have a duty to maintain and repair their buildings using appropriate materials and techniques.   Guiding principles advocate the use of like for like repairs using authentic materials.  But the justification for doing this is not just philosophical.  Technical and aesthetic reasons can be even more important.  Selecting a stone which is to be pieced in or used to replace others in an old wall cannot be done by a visual inspection alone [1].  The old wall will have weathered over time and its appearance will have changed, noticeably from the effects of organic growth, especially lichen.  The stone itself will have been affected by the way that the other stones and mortars around it have performed over time and its exposure to the elements.

It is of course, highly likely that stone for replacement or repair coming from the original source will perform the best.  Although initial appearance will be different it will weather the same way and should start to match the host stones.  Indeed the type of lichens and other plants attracted are partly determined by the minerals in the stone, so a reasonable match can be expected.  The minerals and pore structures of the new stone also need to be compatible with those of the surrounding stones.  A recent report [2] from Scotland showed the harm that can arise where alternative stones are selected which appear similar but are in fact, not compatible.

Over the years, Historic England has been directly involved in searching for and sourcing appropriate stone for many buildings.  In some cases the original sources are no longer available, or have not been worked for decades.  Two recent examples were carried out during the Roofs of England campaign which sought to try to rejuvenate stone slating in England.

Small-scale quarrying: Pitchford Church  The nave roof of Pitchford Church [3] near Shrewsbury needed to be re-roofed.  Harnage stone-slates had not been produced commercially for over a century.  Old geological maps and other records located previous and potential sources which were investigated.  Park Wood quarry was selected, not just because it was the original source of stone for the Church roof, but because the physical characteristics of the stone were eminently suitable.  Most importantly, there was a willing land-owner and although the site was a listed parkland, there was a great deal of encouragement and help given by Shropshire CC mineral planners.  The delving took six weeks and although it was carried out in the wettest month in Shropshire since 1841 sufficient stone was won to recover the nave of the Church and also supply three other listed buildings in the area.  At its height the quarry presented quite a scar on the landscape but four months later it was fully restored.  Planning permission has been renewed in case Harnage stone is needed again.

Dore Abbey  70,000 new stone slates were needed to repair the roofs of Dore Abbey in Herefordshire.  There was a great deal of local enthusiasm for sourcing the stone locally because it could provide farmers with an alternative income following the ravages of foot and mouth disease.  Again, a very helpful mineral planning authority eased the difficulties of obtaining consents for these small, temporary delves.  Significantly, the Herefordshire Mineral Planners pre-empted public objections by consenting 1/10 hectare areas but once the quarry proved to be well managed quickly extended the consent in time and area, when the initial stone was worked out. Old red sandstone slates are now available again for repairing these distinctive roofs throughout Herefordshire and the Welsh Marches.

Difficulties sourcing supplies Those two cases were relatively rare examples where new delves have opened and successfully supplied material.  It is becoming ever more difficult to do this for a number of reasons.  Some former quarries have been worked out or built upon or the land is used for another purpose.   But the biggest constraint comes from objections from local residents or special interest groups (such as ramblers, nature conservation bodies etc) or from other environmental designations.  Many former workings make excellent nature reserves and are now designated as SSSIs or County Wildlife sites.  European designations cover other sites and to date, virtually all proposals to win material – even on a temporary basis have been resisted.   SSSIs which are designated because of their geological interest, though may be permitted because the new workings could expose new faces and other material of interest.

The Roofs of England campaign was based on research carried out in the South Pennines [4] including the Peak District National Park where there are particular problems.  But even outside the Park, in areas where there are no environmental designations it can be extremely difficult to obtain consent.  Re-opening a former quarry at Moorhays Farm, near Chesterfield for a modest amount of stone slates has taken five years to obtain consent because of concerted objections from residents in the area [and still in 2016 has not gone into production].

If new supplies are not forthcoming, then the vacuum is filled by re-using slates from other buildings which either means cannibalising farm buildings (often significant features in the landscape) or theft which is becoming alarmingly common.  The alternatives are to use man-made concrete substitutes or importing stone from India & the Far East.  Whilst the latter may well provide natural products, none of them have been tested and as yet, we have no indication as to how they will perform in the English climate. It is of course, hardly sustainable to transport stone half way around the world whilst local sources are denied for environmental reasons.

Opening quarries for small amounts of building or roofing stone can be a difficult process.   Both quarrying and dressing are still essentially hand-crafted operations and with relatively small outputs, profit margins are small.  But where there is a willing operator/entrepreneur and most importantly, supportive land owner and planning authority and decent supply of material; then much-needed stone can be obtained.

Land owners often have potential sources of material which have been used in the past to repair and maintain their own buildings.  More will be needed.  To assess where the priority lies for roofing will require a condition review of a sample of their stone roofs followed by an assessment of which particular stones are needed for repair and which are in short supply.  Hopefully, the original quarries lie on their own land, and can still provide good fissile material.  If there are good reserves, they could supply stone for other roofs in the locality as has happened at Dore Abbey for example.  This would be a major boon to local conservation efforts, as well as potentially providing income for the land owner.  English Heritage would be happy to share its experience of opening small quarries and processing the finished stone slates.

Chris Wood  English Heritage

[1] A Technical Advice Note, Selecting and Sourcing Stone for the Repair of Historic Buildings. English Heritage Customer Services, PO Box 569, Swindon SN2 2YR  Tel 0870 333 1181  Fax 01793 414 926 .

[2] The Performance of Replacement Sandstone in The New Town of Edinburgh.  Research Report  TCRE, Historic Scotland 2004. Edinburgh 

[3] This is written up in detail in English Heritage Research Transactions Vol 9:  Stone Roofing. pp128-156. English Heritage 2003.  James & James, London