Contents Methods of repairing and consolidating stone buildings John Ashurst Structural failure and repair Ralph Mills 55 The selection of stone for repairs David B Honeyborne Mortars for stone buildings John Ashurst 71 78 Traditional handworking of stone: methods and recognition Peter Hill Earthquake damage to historic masonry structures Alejandro Alva Balderrama 97 107 The repair and remedial treatment of the East Block Parliament buildings, Ottawa, Canada 114 Keith Blades and John Stewart Cleaning masonry buildings John Ashurst 125 Surface treatments 155 David B Honeyborne, John Ashurst, Clifford Price and Keith Ross The conservation of stone monuments in churches John Larson The conservation of stone sculpture in museums John Larson 185 197 12 The museum display of architectural features Deborah Carthy 13 The cleaning of painted stone Clare Finn 14 The cleaning and consolidation of the stonework to the Annuciation Door, Chapter House, Westminster Abbey 219 Keith Taylor, Christopher Gradwell and Teresa McGrath 208 14 Appendix Limewashing John Ashurst Appendix Effects of large numbers of vistors on historic buildings David Honeyborne Appendix The use of air-abrasive cleaning techniques for stone building surfaces Peter Moss Appendix The analytical approach to stone, its cleaning, repair and treatment Nicola Ashurst and John Kelly Index 245 229 231 237 240 Methods of repairing and consolidating stone buildings JohnAshurst Introduction A stone building of any age and condition requires an experienced practitioner to assess its real state and its repair and maintenance requirements The objective of this and subsequent chapters is to assist the general building practitioner to become more familiar with the problem of stone construction and the various repair and maintenance options, rather than to discuss matters of general survey and inspection There are as many dangers associated with unnecessary or incorrect interference with masonry structures and surfaces as there are associated with neglect Whilst the interference problem is not new it is tending to take over from neglect as the prime enemy of historic stone buildings in the more affluent areas of the world Typical examples of harmful intervention include: Introduction of massive concrete stitching or beams into cracked but stable masonry Introduction of large quantities of cement grouting Introduction of large quantities of polyester or epoxy resin grout Unnecessary replacement of worn and heavily weathered stones Widening of original joint widths and spalling of arrises by the use of cutting disks and wedgeshaped chisels Superficial pointing of joints with cement-rich or resin-based mortars Alteration of original joint profiles Damage by air-abrasive and disk cleaning Residual damage associated with acid and alkali cleaners 10 Use of inappropriate surface treatments, such as water repellents, consolidants and anti-graffiti coating of the wrong type In some cases the work carried out will not be physically harmful, but when stones are replaced unnecessarily or the original joint profiles are altered this will have a de-valuing effect on the building The keys to good masonry conservation are undoubtedly experience in problem recognition and diagnosis, competent specification, minimal physical intervention and maximum technical site skills Clearly these desirable elements need the involvement of more than one discipline, but it is likely that the central co-ordinating discipline will be the architect's On pages 2-3 the architect's plan of approach to a masonry building is suggested in the form of various action options Unless the problem is very simple, however, the architect should involve the archaeologist, art historian, specialist engineer, analytical chemist, masonry technician and stone or sculpture conservator at an early stage The need to examine minutely and to record before anything is altered or repaired is paramount In some situations there may be no money available for any work for many years In these cases recording should be given a high priority Photography, photogrammetry and monitoring are all important, sometimes critically so, but so, still, is the making of drawings, the taking of moulds and casts and the making of accurate templates of original profiles Although there are some highly sophisticated recording techniques, and in some parts of the conservation world there is so much specialized technical backup that simple site observation becomes relegated, there will never be a substitute for close site observation based on long experience All techniques must be subordinate to and supportive of personal site survey Sites with ruined masonry and roofed and occupied masonry buildings have various repair and maintenance requirements in common, but ruined REMEDIAL WORK TO MASONRY : SCOPE AND OPTIONS tiooard d ~ a g n o s i s c o n d i t i o ~ usefolly be of car, categories : A :THEWALLS - :THE C t THE JOINTS [~tro~.or-l &ition] considered in tbe STONES [ i d i v i d w O y ~ A :T H E WALLS If so, b e r-ns musk be know* A r e they heyleanins, b u l g ~ h ~ , histing, f r a c t u r i n g Are the s h u c t u r a l p r o b l e m s real a n d "live'; o h a v e hey already k e n resohted ? r CAUSES O F PROBLEMS may be : UNEQUAL SElTLEMENT bnwnsistency in [beb r i n g cdpacikyof [he ground, mlning 3ub5idence, u n e q u l loacls from different buildi ngelernenks ] COLLAPSE- O F AKCUES VAIJLTSOr BUTTeESSES Iknock-on e f p t s from d e s f r o c t ~ o n essentral s ~ ~ ~ r b of orcounter-t r u s t e l e m e n t s ] GENEeAL JNSTAB~L~TY [ d u e 10 sbtuctoral alterations ex 1os10nearth vake, robbtng ~ i o wW5hlr78 cclt 0~&,I &re anb Jon%l ~, INAPPPOPEIATE STeUCTUeAL Lstre~5egirnpoxd by rigid restralnt5 and h e s , u n e c e w buttressing, Strona resin - based o r cementitious g r m t s INT€EVENTION REMEDIAL W O l Z K T O WALLS Must be preceded by detaikd site invesh$?atioo and Jurvey, including accurdte monitori9 Work should n o t be viswlly Eemedial Work m y include SECTIONAL obtrusive : - m u s t not impose new problems on fbe fabric an @ PILING UNOELPINNING INSEETION OF HIDDEW WALL H€AD INSEETION OF HIDDEN LINTOLS GROUTING BY GeAVlTY OR 0: THE , EING AND HANGING SYSTEMS WITH LOW PRESSVEE BEAMS, ANGLE scaling, s be u L I M E , F Y ASH, WHITE COvlElJT L kept ; some on -site moniton'n need to m t i n v e indefinitely OF rw:rifl$, a ocd us1 s p l i t , real mus PROBEMS W M S FCfZ A E C H E S STONES Are the spallin t& If CAUSES FWCTVLZES BEAMS Full records cf all stroctural inkrventioos most ma?/ @ 5TITCHING Ace055 may be : dispgured and pi tHn8 ? by skin% latorakory analysis if ncces"y calcareous, doiomitic,argillacea~ W"S s m S~OXS a m ~tlrbk espeaally t o s h e l k r e d z o n e s L I D ATTACK ON BINDING MATfSIX O F STONE [especiall and FOeMATION ON WLPHATE 5t -4 CONTWiZ SCALE FWMATION 4SANDSTON&S OTUEe SRLT CRYSTALLISATION FEEZING FrELE @ WEATCIE~(~.IG CUT TWSTING OF IEON VENTS C~AMP [ espec~all~ to WEATHEZING AND SNAKES WMPCESSION AFTER D I S C O W ~ A T I O N , PITTING A N D TUEATMEMTS L sa turat;on z o n e s [as=~aked with r i s t n g d a ~ ~ , c e r v l e n ~ ~ r o u ~ i n c o rs t~at ~ b l e n q OAMAGE 5TblNING AND f-fFLOEESCENCE SUEFACE LIMESTONES OF ZQFT Bu>S I N C ~ ~ ~ E C T BEDDING FACTOCES CLfANrNG SPALLING ASSOCIATED w1TH [especially 1rad;CiowI p - e - bkck;ng treztmmts tZfS\/lfDIAL WOCZK TO STONES Must be preceded b J can rehensive tjuw wikh adeqate d nosis wmpated on all d& e a%ddecay., of (hin %c+ioos%d salt b ,h e d ; idenhfation 01 ~ k m e m any d f r e a t w t o unw%a[ 5011rn%mu5t dl50 be made An efevatronal record W I r brqp scale profile debils is neccs? on &id., each stone i s i&nti@bk atld 37 vp m y be a m e a s r e d s y yrrccfed w refcrcnced I h i ~ record hob a m n e w u r v e y work may include : - !evegal Modiflation o Modilidid @ freak 401 rnvrt- work and All CUT WT exkerna environment Lproviding wesfhe! Wapcr &m!s OF internal envlkoownf AND -PLACE OK ~ phot06r6 be rmd'd" r o t e c h ' ~ , routing reo[d a m p - rn!roddlon 5, d ~ ir e t proof, Tern bra& w] ! h v ~ , d i k tmperatufe controls, restricfiz~CX visitor numbers EE.FACE W,TH STONE MA-TCHI~-IG [ru 0riq;nc71 p1-ofl'ie~J CUT OUT AND PIECE - IN WITH I N EXISTING STONES , IN MATCHED SRWE o CUT WT AND FILL [lime based fills+r WITH MORTAR oraoyllc I i ~ s i - m e , ~ ~ based FIIs jbr sandstone &c ensurin D ~ L LG , W T bND rmea ble m i+ no 3&'