Inform Guide

Mortar may be inserted into the joint from a The actual techniques used will depend to a large surfaces are dampened before pointing work board held adjacent to the wall face by using extent on the preferred tried and tested working starts. Any accidental spillage or smearing Useful contacts: the side of a thin steel blade or similar tool. If method and the craft skill of those working on the should be washed off immediately with a Historic Scotland, Longmore House, Salisbury the joint width allows, regularly inserting a thin job. Whatever system is employed it is important fine jet of clean water, but this could be Repointing Place, Edinburgh, EH9 1SH: 0131 668 8600 wooden (or other material) spatula into the joint to ensure that an adequate depth of mortar is avoided in the first place by setting some www.historic-scotland.gov.uk to compress the mortar as work progresses will inserted into the joint and bed. Normally a temporary protection in place below the Ashlar help ensure that the joint is properly filled. minimum of 30 to 40mm would be anticipated. work area to contain any spillage. Historic Scotland TCRE Group Publications Department: To press mortar into the joint from the face of As the mortar starts to cure it should be tamped Ashlar built walling was frequently 0131 668 8638: Fax - 0131 668 8669 Masonry the stone, a ‘sausage’ shape of mortar is formed back with the tip of a bristle brush to eliminate constructed with slightly tapered blocks to Historic Scotland Conservation Bureau & and pressed against the protected stones’ surface any shrinkage cracks. Once it has firmed up assist in achieving very fine joints on the Technical Enquiry Service: 0131 668 8668 around the joint with a flexible spatula or blade, sufficiently the mortar surface can be finished face. As a result, the vertical joints and, [email protected] or (wearing protective gloves) with the ball of the if required by lightly scraping it with a small sometimes, the horizontal bed joints may be Historic Scotland Investments and Projects Team: thumb. Deep filling of the joints can be difficult wooden spatula or similar instrument. Where considerably wider within the depth of the 0131 668 8801: Fax - 0131 668 8788 with this approach. protective tape has been used this should only be wall. If this is the case, it may be necessary [email protected] removed once the mortar is sufficiently dry and to place a backing or plugging of waxed The process of injecting mortar is unlikely to be before it becomes hard. In this way any disruption string or similar material, or a wedge of hair Historic Scotland Inspectorate: successful except, possibly, where a very fine lime to the mortar caused by the removal of the tape mixed with a little lime mortar, to prevent Listed buildings: putty mix is used. Caution is required because the can be pressed back into place. the new mortar from disappearing endlessly 0131 668 8745: Fax - 0131 668 8722 size of the nozzle required to inject mortar with into the depth of the wall. [email protected] a fine sand filler can be too large for use on very Care should also be taken to avoid spilling any of Ancient monuments: fine ashlar joints, and control over the pressurised the new mortar onto the underlying stone faces. Repointed ashlar masonry also requires 0131 668 8777: Fax - 0131 668 8765 mortar as it comes out of the cartridge can be This will cause staining that is difficult to remove. careful aftercare as work progresses. This [email protected] problematic. Permanent staining is less likely to occur if the should be done through placing suitable mortar is of the right consistency, and if the stone protection, such as sheets of damp hessian, Further reading against the wall face until the mortar is TAN 1 Preparation and Use of Lime Mortars cured. Especially in hot weather conditions, Historic Scotland, Reprint 2005, the hessian should be regularly and lightly ISBN 1 903570 42 5 Repointing ashlar sand or stone dust as an aggregate, the particle spraying with a fine water mist to stop the Mortars in Historic Buildings – Literature Review So that it could be used in the thin joints size should be no larger than a third of the mortar from drying out too quickly. Historic Scotland, 2003, ISBN 1 903570 82 4 and beds a white putty lime - a mix of lime minimum joint width. In all situations, it is The Repair of Historic Buildings in Scotland Historic Scotland, 1995, ISBN 0 9517989 2 8 putty and whitening, with a little linseed advisable to have a mortar analysis carried out The Conservation of Architectural Ancient Monuments oil - was the original material of choice for on the original mix so that a matching mix in Scotland – Guidance on Principles pointing ashlar walling. Matching repointing can be more accurately achieved mortar should not be spread over the face Lime mortar can be inserted into the narrow Historic Scotland, 2001, ISBN 1 903570 32 8 of the individual ashlar blocks, and should ashlar joint and beds in three ways – by be carefully limited in its application to the using a suitably dimensioned thin tool that thickness of the joints and beds surrounding easily fits into the joints; by pressing in the each block. To assist with the process of mortar from the face of the stone; or by inserting this mix into the joints a small careful injection using a proprietary tool. Each of these techniques has advantages quantify of natural (horse) hair can sometimes Principal author: Ingval Maxwell be teased into the mortar before use. If the and disadvantages, and a combination of Published by Technical Conservation, Research and Education Group, May 2008 repointing mortar also needs to include fine techniques may be required on one job. Historic Scotland, Longmore House, Salisbury Place, Edinburgh EH91SH Tel: 0131 668 8638 Fax: 0131 668 8669 www.historic-scotland.gov.uk email: [email protected] all photos © Ingval Maxwell sustainable material from Produced House 4/08 The Mortar may be inserted into the joint from a The actual techniques used will depend to a large surfaces are dampened before pointing work board held adjacent to the wall face by using extent on the preferred tried and tested working starts. Any accidental spillage or smearing Useful contacts: the side of a thin steel blade or similar tool. If method and the craft skill of those working on the should be washed off immediately with a Historic Scotland, Longmore House, Salisbury the joint width allows, regularly inserting a thin job. Whatever system is employed it is important fine jet of clean water, but this could be Repointing Place, Edinburgh, EH9 1SH: 0131 668 8600 wooden (or other material) spatula into the joint to ensure that an adequate depth of mortar is avoided in the first place by setting some www.historic-scotland.gov.uk to compress the mortar as work progresses will inserted into the joint and bed. Normally a temporary protection in place below the Ashlar help ensure that the joint is properly filled. minimum of 30 to 40mm would be anticipated. work area to contain any spillage. Historic Scotland TCRE Group Publications Department: To press mortar into the joint from the face of As the mortar starts to cure it should be tamped Ashlar built walling was frequently 0131 668 8638: Fax - 0131 668 8669 Masonry the stone, a ‘sausage’ shape of mortar is formed back with the tip of a bristle brush to eliminate constructed with slightly tapered blocks to Historic Scotland Conservation Bureau & and pressed against the protected stones’ surface any shrinkage cracks. Once it has firmed up assist in achieving very fine joints on the Technical Enquiry Service: 0131 668 8668 around the joint with a flexible spatula or blade, sufficiently the mortar surface can be finished face. As a result, the vertical joints and, [email protected] or (wearing protective gloves) with the ball of the if required by lightly scraping it with a small sometimes, the horizontal bed joints may be Historic Scotland Investments and Projects Team: thumb. Deep filling of the joints can be difficult wooden spatula or similar instrument. Where considerably wider within the depth of the 0131 668 8801: Fax - 0131 668 8788 with this approach. protective tape has been used this should only be wall. If this is the case, it may be necessary [email protected] removed once the mortar is sufficiently dry and to place a backing or plugging of waxed The process of injecting mortar is unlikely to be before it becomes hard. In this way any disruption string or similar material, or a wedge of hair Historic Scotland Inspectorate: successful except, possibly, where a very fine lime to the mortar caused by the removal of the tape mixed with a little lime mortar, to prevent Listed buildings: putty mix is used. Caution is required because the can be pressed back into place. the new mortar from disappearing endlessly 0131 668 8745: Fax - 0131 668 8722 size of the nozzle required to inject mortar with into the depth of the wall. [email protected] a fine sand filler can be too large for use on very Care should also be taken to avoid spilling any of Ancient monuments: fine ashlar joints, and control over the pressurised the new mortar onto the underlying stone faces. Repointed ashlar masonry also requires 0131 668 8777: Fax - 0131 668 8765 mortar as it comes out of the cartridge can be This will cause staining that is difficult to remove. careful aftercare as work progresses. This [email protected] problematic. Permanent staining is less likely to occur if the should be done through placing suitable mortar is of the right consistency, and if the stone protection, such as sheets of damp hessian, Further reading against the wall face until the mortar is TAN 1 Preparation and Use of Lime Mortars cured. Especially in hot weather conditions, Historic Scotland, Reprint 2005, the hessian should be regularly and lightly ISBN 1 903570 42 5 Repointing ashlar sand or stone dust as an aggregate, the particle spraying with a fine water mist to stop the Mortars in Historic Buildings – Literature Review So that it could be used in the thin joints size should be no larger than a third of the mortar from drying out too quickly. Historic Scotland, 2003, ISBN 1 903570 82 4 and beds a white putty lime - a mix of lime minimum joint width. In all situations, it is The Repair of Historic Buildings in Scotland Historic Scotland, 1995, ISBN 0 9517989 2 8 putty and whitening, with a little linseed advisable to have a mortar analysis carried out The Conservation of Architectural Ancient Monuments oil - was the original material of choice for on the original mix so that a matching mix in Scotland – Guidance on Principles pointing ashlar walling. Matching repointing can be more accurately achieved mortar should not be spread over the face Lime mortar can be inserted into the narrow Historic Scotland, 2001, ISBN 1 903570 32 8 of the individual ashlar blocks, and should ashlar joint and beds in three ways – by be carefully limited in its application to the using a suitably dimensioned thin tool that thickness of the joints and beds surrounding easily fits into the joints; by pressing in the each block. To assist with the process of mortar from the face of the stone; or by inserting this mix into the joints a small careful injection using a proprietary tool. Each of these techniques has advantages quantify of natural (horse) hair can sometimes Principal author: Ingval Maxwell be teased into the mortar before use. If the and disadvantages, and a combination of Published by Technical Conservation, Research and Education Group, May 2008 repointing mortar also needs to include fine techniques may be required on one job. Historic Scotland, Longmore House, Salisbury Place, Edinburgh EH91SH Tel: 0131 668 8638 Fax: 0131 668 8669 www.historic-scotland.gov.uk email: [email protected] all photos © Ingval Maxwell sustainable material from Produced House 4/08 The The nature of ashlar Practical After flushing out the open joints and beds with a jet of clean With Scotland’s geological diversity, a wide range considerations water, and damping it down, the of stones have been used in the creation of ashlar Although the basic principle of process of inserting fresh putty buildings although, in most parts of the country, only using lime-based mortars lime mortar into the fine joints the use of sandstone predominates. Rough quarry applies to the repointing of ashlar should start by taping over the blocks were carefully cut into precise cuboid stone work, the fine joints in the stones’ arrises with heavy duty shapes with a tooled or smooth polished external build require additional care whilst sticky-backed tape, or similar faces. Edges were cut square and true so that each undertaking such work. The care material, to protect the adjacent block could nestle closely with its neighbour when and attention which was exercised stones against staining and set into the wall. Courses of stones were cut to during the building process mechanical damage. Care needs exactly the same height, in random lengths, and needs to be recognised whenever to be exercised in the choice laid with a “broken bond” so that the middle of repointing repair work is carried of the protective tape as some the blocks on the next course sat directly above out and, consequently, the amount brands can leave an adhesive Introduction the vertical joint on the underlying course to give of time and skill required to do sound or resistant to removal it will be residue on the stone’s surface and this can be the wall maximum load-bearing strength. Water vapour egress through the lime mortar joints of ashlar the work properly should not be necessary to evaluate the likely damage that The Romans brought the technique of squaring difficult to remove. Before work starts, the masonry needs to be recognised as an important part of how underestimated. could be caused by leaving it in place against and building regular sized stone blocks - ashlar - to chosen tape should be tested in a discrete The surface finish of buildings with ashlar walling traditional buildings breathe and cope with rain water. If this the damage which would be caused by its location to determine if this will happen. Scotland. The technique then fell into disuse but, differed from that of building with rubble walling process is prevented from happening a number of damp related A total repointing may not always removal. Sometimes the best practical option with the coming of the great monastic orders from in that the use of the lime mortar was limited to problems and consequences can emerge. The most common cause be necessary if only part of the is to leave the cement mortar in place, accept the 11th century onwards, building in ashlar was filling the fine joints and beds which surrounded of such problems is the use of cement-based mortars to repoint original mortar has decayed. A the existing appearance and, possibly, any revived as revealed by the construction of their each block. Joint and bed dimension generally the walling and this should be avoided in all repair work. partial repoint using a mortar mix ongoing related masonry decay. great Abbeys and associated building ranges. On only amounted to a few millimetres in thickness similar to the original is often all at the surface, with this reducing to a “paper Commonly cement mortar is either smeared over the stone face that is required. This cautionary Preparing ashlar for the defensive front, the use of ashlar was relegated thickness” as a result of the accuracy in block or formed into projecting straps of mortar that cover the joints approach also helps to eliminate repointing to the creation of dressed stone surrounds to doors, and beds in addition to parts of the stone. Both approaches cutting during Georgian times. During this some of the risk of damage to the Before starting any repointing work, a detailed encourage rainwater to penetrate and be retained within the wall windows, corners and other structural features period, the exposed face of the ashlar block may stones that can occur during the evaluation should be carried out to determine structure and this can lead to significant stone decay. during the building of Scotland’s medieval castles. also have been adorned with a chamfer, which various stages involved in repointing. the full extent of the required work. It is In more peaceful times, by the 17th and early 18th created the illusion of V-shaped joints when the Other situations can emerge where also essential that the work is carried out in centuries it was being used more extensively to blocks were put together, or were tooled in such a complete repoint is essential e.g. appropriate weather conditions, and that it a way as to emulate a rock cut finish. In each where the effects of weather on is protected from the effects of both sun and create fine dressed stone facades of the great country case, the mortar joints and beds were of small softer sandstones have had their mansions such as Kinross, Duff and Hopetoun, and rain until it is cured. Care will be essential dimension. faces more generally eroded. when raking out the joints and beds, and it is rich merchants’ houses in towns and cities. generally inadvisable to use chisels or power On no account should a cement tools to cut out the decayed or loose mortar Although well-established by this pedigree it was based mortar be used to repoint from the fine joints due to the risk of damage only from the mid-nineteenth century, when stone ashlar but, if at some time in to the stone. the building’s past, superficial quarrying and working techniques became more cementitious over-pointing has mechanised and economic, that it became possible Decayed mortar should be removed by been inappropriately applied, this carefully picking it out with a thin steel hook, to build domestic dwellings that incorporated ashlar can sometimes be removed by or by easing the redundant material out by facades. Found equally on city tenements, villas, and carefully picking it off without means of a hand-held hacksaw blade inserted rural farmhouses this approach to building lasted damage to the stone’s edges. Where into the joint and gently pulled forward. into the early decades of the 20th century. the cement based material is still