rectangular apse or presbytery covered with a barrel vault. (fig.l). · 2014-05-20 · rectangular...

Study of the deterioration of the ancient stone

walls of San Antolin de Toques in Galicia, Spain,

and the influence of the substitution of traditional

lime mortars.

M.C.I. Martinez*, A.N. Seoane, J.R.V. Roman!

^Department of Construcciones Arquitectonicas, Universidad de La

Coruna, 15192 La Coruna, Spain.

Abstract.

Modern appreciation of new artistic values in ancient buildings have often given rise to a wrongopinion of the role played by traditional materials, and has frequently caused the elimination oftraditional lime renders that were used to protect ancient walls from atmospheric agents.Thishas become worse in the XX century since the use of new materials developed during theIndustrial Revolution has not always fit in traditional building technology and has caused thedevelopment of different deterioration processes.

The objective of this paper is to show the consequences of a practice carried out in San Antolinde Toques, frequent in restoration works, based in both removing exterior renders andsubstituting traditional mortars of the joints, on the outside of the wall, by cement ones,unaware of the ancient materials properties for the conservation and maintenance of ancientwalls and the contribution of new ones to the development of a general deterioration process.

In this paper it will be analysed the present state of deterioration of the Church San Antolin deToques in Galicia, Spain, as well as the specific factors that have contributed to it. For thispurpose different samples from the wall have been collected and analysed.

1. Introduction.

San Antolin de Toques is a Church located on a steep slope on the east side ofmount Bocelo, which is 600 meters above sea level and about 10 Km awayfrom Melide, in the province of La Coruna, Galicia, Spain.

Transactions on the Built Environment vol 26, © 1997 WIT Press, www.witpress.com, ISSN 1743-3509

222 Structural Studies, Repairs and Maintenance of Historical Buildings

Although it has been known since 1067 as a monastery, it is very difficult toknow the time when it was built due to the fact that it is made up by a series ofsuccessive buildings and rebuilt remains, which have even been modifiedsubsequently. However it is considered to be primitive Romanesque, having itsorigin in the second half of XI century, although some parts are Visigothic. It isformed by a rectangular nave, with its west side extended and rebuilt in 1812,and covered with a modern wood roof structure. On the east side there is arectangular apse or presbytery covered with a barrel vault. (Fig.l).

Fig.l. Plan of the Church of S. Antolin de Toques in 1972. Luengo Martinez 1.

Walls technology system used in San Antolin de Toques, had been developed inRoman times and widely used through history until XIX century. It is the "opusemplectum\ where the core of the wall is made up of stones or rough-hewnstones or fragments of stone, mixed with lime, lime-earth or clay mortars, andcovered with stone/brick facing walls, whose materials and building qualityhave changed a great deal through history according to different factors: localeconomy and technical development, and the properties of the local materials.These two facing walls had to satisfy two different requirements: on the onehand, they had to be consistent enough to be used as shuttering for the interiorcore, on the other they should have a regular surface on the outside, to resistatmospheric agents, or be able to support a lime render, if the stone was notsuitable, which would protect the wall.

Although there are many examples characterised by the use of facing walls ofenough quality to be on the outside, there are others, the majority, that becauseof the stone used, were not resistant enough to absorb atmospheric weathering.In this case it was necessary to protect the stone of the facing wall with aprotective and decorative lime cover. In fact, mortars have been one of the mostuseful materials used outside the walls, in all cultures, due to their infinitefinishing possibilities and their optimise protective and maintenance properties.


Structural Studies, Repairs and Maintenance of Historical Buildings 223

Romanesque churches built in rural environment have been characterised by theuse of local materials which were worked and elaborated according to differenttechnical development and local materials properties, and building materialscoming from further places were usually preserved in order to be used insignificative architectural elements of representative buildings.

The constructive system used in San Antolin de Toques is characterised by theuse of materials coming from other buildings and by the election of severaltypes of materials coming from the environs, which caused the use of irregularsizes and different kinds of stone in the outside of the walls. We can distinguishthe following wall types: a) Parts built with big ashlars, on the south facade ofthe apse, b) Parts built with big ashlars alternated with smaller ones, whichdon't even reach the same height, in the high part of the south and east wall, c)Lines of big ashlars which alternate with two lines of small, narrower ones inthe south facade, d) Parts with lengthened ashlars of different sizes, in the northfacade, e) Rubblework in the north and west facade and in the west end of thesouth facade. (Fig.2,3)

Fig.2. View of the south and west facade. Detail of the construction of thedifferent walls and the materials used : paragneis mixed with some aplitaashlars in the south and Sobrado Ortogneis inner facies in west facade.

The lack of uniformity of the masonry together with the evident deterioration ofthe ashlars in the main, south facade, the excessive humidity conditions in theinside of the church and the progressive deterioration of its Gothic paintings,show the elimination of possible renders and the substitution of the traditionalmortars of the joints by cement ones, as important factors that could havecontributed to the development of the present situation.



Fig.3. Construction detail of north facade made of Sobrado Ortogneis innerfacies.

2. Methodology and Materials.

In order to characterise the present situation of deterioration and determine thefactors that could have contributed to them, information and samples have beencollected in January 1997, and different methodologies have been applied.

2.1 Study of the masonry materials.

1. Identification of the stone used in the outside of the wall as well as thedeterioration process it suffers. Unnecessary destructive methodologies havebeen avoided, and there have only been analysed samples from the surface ofthe stone, to identify the degradation of minerals composition degradation.Micro-organisms from the surface of the stone have been also collected andidentified.

2. Study of the quarries of the area and identification of the origin of the stoneused in the walls. For this purpose a geological map of the area has beenused, IGME2.

3. Characterisation of joint mortar used on the outside of the walls in lastinterventions. Different mortar samples from the joints of the outside of thewalls of the Church have been taken and analysed in order to define theircomposition, the binder and the aggregates used in the mixture. For thispropose the following methodologies have been applied: Calcimetermethods, Infrared spectrometry, X-ray Diffraction, and optical microscopyobservations of polished sections.

• Calcimeter methods are based on the determination of Calcium Carbonate ofthe sample by means of the measurement of the Carbon Dioxide released,when it comes into contact with Hydrochloric Acid and of the insolubleresidue after the reaction. From this establishments we can define thefollowing mixture proportions:% Ca CO3, coming from the binder, lime orcement or even from calcareous aggregates, if there exist in the mixture.%Insoluble residue from the non calcareous aggregates used or from cement



compounds. %Soluble, from cement salts or from organic material of claymortars.

• X-ray Diffraction. Is a semi-quantitative methodology, which shows themineralogy composition of the mortar.

• Infrared-spectrometry applied to mortar samples treated with PotasiumBromide, is a suitable method to confirm the presence of cement contents,which in many cases, as a result of the hydration of the mineralcomposition, is not possible to detect with XRD diagrams.

• Optical microscopy observations of polish sections. It is possible to identifythe kind of sand used in the composition and interpret the results obtained bymeans of calcimeter methodology.

2.2 Identification of the deterioration process developed in the interior.

1. Registration of temperature and relative humidity in the interior of thechurch. Interior atmospheric humidity has been measured with a psycrometerinstrument. To determine humidity conditions of the wall, superficialmoisture was obtained with an electronic meter by means of variations in theplaster's electrical resistance. Despite their inaccuracy when salt depositionsare present on the wall, it gives a valuable information about estimatehumidity conditions of the walls. Series of measurements have been made onthe different walls and at different heights.

2. The existence of salt deposition on interior wall surfaces. By means of anelectronic instrument estimate values of salt depositions on the interior sideof the walls, have been registrated. Measurements series have been recordedat different height, in the interior side of the walls.

3. Identification of micro-organism growth. Samples have been collected fromthe mural paintings of the interior.

3. Results and Discussion.

3.1 Study of masonry materials.

The observation of the stone of the walls shows the use of different types, in theconstruction of the church. The stone used in the walls are diverse, even if theirorigin can be considered from the area. From a geological point of view SanAntolin de Toques belongs to the Group called Ortogneis of Sobrado, within theDomain of Ordenes Serie. It is a rock which presents two fades: outer facies (2)and inner facies(l). The church is located in the second type of rock. It is a veryresistant material against erosion as it can be checked on the rock exposure near



the church. The outer facies of the same rock Ortogneis of Sobrado, appears tobe, however, less resistant to atmospheric agents. (Fig.4)

(2) ,\%,n,,( 3) Mciab15} Aul.lH

Fig. 4. Geologic map of the area of S. Antolin de Toques.

On the north facade the use of Ortogneis of Sobrado, inner facies, has beenidentified, which, because of its hardness and the lack of resources, was used insmall rubblework which were extracted out taking advantage of the foliatedstructure of the rock. On the contrary in the south, main facade of the church,and in the apse walls, mostly built with regular ashlars of big dimensions, adifferent type of rock was used: a paragneis, schistoric granite, which is foundwithin the outer facies of Ortogneis of Sobrado. This kind of rock ischaracterised by its high degree of alteration, which has caused a great loss ofmaterial in the ashlars of the walls, and even the "recent" substitution of someof them due to its degradation (sample analysis of these ashlars denote animportant transformation of its minerals, micas and feldspars into amorphousmaterials, been quartz the only unaltered mineral). In fact the use of this type ofstone even as a wallbase has originated an important algae coloniesdevelopment up to one meter from the floor: Cyanobacteria (Chlorogloeamicrocystoides, Gloeocapsa magma, Gloeocapsa sp, Oscillator ia sp,Phormidium tenue), and Green algae (Klebsormidium Flaccidum, Stichococcusminutus, Trebouxia sp, Trentepohlia sp).

The choice and use of these kind of rock, outer facies or schistiric granite, beingof worse quality than the local one, to make ashlars and the construction of themain facade of the church, is attributed to the economic difficulties at the timeof its construction and to the declining techniques used compared to theprevious ones of Roman origin, or those developed during advancedRomanesque. In fact, the process of deterioration suffered by the ashlars of bigdimensions in the south wall and apse mainly, causes in some of them a loss ofup to 6 cm. with reference to the facade line, and others have already been



replaced due to its terrible state of preservation. The bad state of conservation ofthe stone makes us think that perhaps the stone used was already in weatheredcondition in the quarry. The decision to use it could have been the easiness to beextracted and elaborated.

The building of the masonry of the south facade and apse besides the littleresistance of the stone used, is characterised by the poor construction ofimportant architectonic elements (the missing keystone of the semicircular archin windows, the fan division of stone in the arches, the missing keystone of thearch in the main facade), what together with the importance of thecommemorative value of ancient buildings, e.g. Riegel 3, which made ancientmansons use building techniques and materials to ensure its preservation forfuture generations, make us think, in the possibility that they were originallycovered, how ever the choice of a kind of stone from a distant area, not suitablebut easy working and the perfection of the ashlar joints make the initial ideapossible unlikely and the building characteristics are attributed to a low buildinglevel of that time.

Interestingly, for the extension carried out in 1812, rubbles of the sameOrtogneis of Sobrado, central facies used in the north facade, but with moreirregular shapes and sizes, have brought about the appearance of wide joints andthe need to protect their porous mortars with protective lime coats to avoid thatexcessive amounts of water may enter the walls. Although in later restorationsthe coating has been eliminated, its previous presence has been proved by aphotograph of the church in the 60s has been found in the priest files of Toques,D. Cleto Porto. (Fig.5)

Fig.5. View of the Church in the 60s.

It has also been identified in the cornice impost, of Visigothic origin the use of aleucogranite or aplite, not found in the area, more suitable, than the rocks usedin the walls building, because of its kind of grain, for the sculptural workpresented and durability.



The results of the analysis of the mortar samples collected indicate the presenceof two different mortar compositions, one corresponding to the mortar used inthe south, apse and west facade, type I, and the other corresponding to themortar used in the north facade, type II. (Fig.6). Type I mortar is composed ofpoor cement mortar. The use of Portland cement is identified by X-raydiffraction diagrams, by the portlandite and ettringitte content. The sand hasbeen identified as coming from the near river, by the presence in itscomposition of great amount of continental shells, that have been identifiedunder optical microscope observations and correspond to the aragonite in X-raydiffraction diagrams (fig.7). Sand composition indicates the presence of grainsof quartz, feldspars and aragonite, and quite a great deal of organic material.The high values of CaCO3, too high for the cement content, are explained bythe identification of the continental shells of the sand used. It is interesting tonotice the beginning of the development of cracks in the mortar. (Fig.).Infrared-spectrometry diagrams confirm the presence of cement in type Imortar, by means of the bands of tricalcic aluminate and Energy DisperseSpectrometry analysis shows the presence of sulphur coming from the gypsumof the cement. Type II, is a clay mortar with a high percentage of quartz, andalterated feldspars and micas and much organic material. It presents asuperficial disgregation and high humidity content. No cement content has beenfound. It is, actually, an ancient mortar which hasn't been changed through thesuccessive interventions carried out in the church.

TYPE ITYPE II

CaCO362%0%

INSOL22%87%

SOLUB.16%13%

Fig.6. Calcimeter results of mortar samples.

UJWuAjJ ^10 IS 20 2S

.I HOISI308 Slcrocl

Fig. 7. X-ray diffraction diagram from mortar type I.



3.2 Identification and study of the deterioration process developed.

Atmospheric RH measurements, indicate very high values (70%) and atemperature of 7°C. Walls humidity measurement in the interior, indicates highhumidity content in all facades, even if they present an indicative differentperformance: While humidity contents is very high and constant in height, insouth, west and apse walls, where type I mortar has been used, with averagevalues of 60%, in the north facade, where type II mortar has been used, itdecreases quickly from 40% to 10%. Salt measurements, in the south, apse andwest walls, there cement mortars, type I, has been used in the exterior side ofthe wall, indicate a dangerous salt content, for the integration of the wall. In factwallpaintings progressively fall at the bottom areas and intonacoes in the upperarea of the south facade present a loss of adherence to the wall.

In addition to the elimination of original renders, it has been frequent, inmodern restoration works, like in south, west and apse walls of San Antolin deToques, to change the lime or clay mortars of the joints of the walls, for othersmore impervious and resistant, that could avoid maintenance works, like cementmortars. However, cement has been one of the modern materials which hascaused more damage in ancient buildings, due to the incompatibility of theirimpervious properties with ancient building technology.

Traditional walls, from the point of view of their performance against humidity,is based in an extraordinary construction technology, which avoids theaccess of excessive amount of water inside the structure, by using special drainpieces in the base of the wall, drainpipes, wallbases, eavesend, gutters...etc, andporous building materials, more or less soaking, which important permeablecharacteristics facilitate the evaporation of walls humidity content, whenatmospheric conditions are appropriate, and occasionate acceptable humiditycontents inside the walls. On the contrary, the introduction of cement mortars inthe joints of the walls, avoids the evaporation of water content that can enterinside, thus rising damp, like in San Antolin de Toques, causing a progressiveincrease of water content in the walls. The evaporation of this water contenttakes place through the inside of the walls if permeable materials are used.When mural paintings are used in the interior, a deterioration process appearsdue to the stress of salt deposition and the high relative humidity values of thewalls and air, which can even originate, if temperature conditions areappropriate, the development of micro-organisms, e.g. C. Iglesias4. In thisexample fungi colonies have been localised in the bottom of south wall.

The moisture conditions developed in the walls of San Antolin de Toques,together with the fact that moisture from the water table characterises by ahumidity attack of the entire building with almost perfect uniformity , unless the



building is constructed of different materials, reaching even maximum height innorth and north-east exposures, due to the reduced evaporation resulting fromthe lack of heat e.g. Massari 5, shows the influence of the properties of thedifferent mortar composition used in the joints of the wall.

Actually, this case study is a good example to analyse the different wallsbehaviour to rising damp, when permeable mortars have been substituted byimpervious ones, or when permeable mortars, like clay ones, have beenpreserved, even if they have not been properly maintained and theircomposition is not the best, e.g. Smeaton project 6.

In this case, we can observe that the humidity conditions, caused by rising dampin the south, west and apse walls, where cement mortars, type I, have been used,are much higher than those developed in the north side, where clay mortarshave been preserved, reaching such dangerous values of 60% causing aninevitable general decay of the mural paintings of the interior and a RH of 70 %in the air.

The conservation of the original clay mortars on the exterior of the north wall,and the introduction of rising damp, have originated humidity values of 40 % atthe bottom that decreases very quickly with height to 10 %, that we attribute tothe permeability of the clay mortars when exterior atmospheric conditions areappropriate. Anyway, we think that the suitable maintenance of the mortar inthe joints and the use of lime in the composition of the mortars would improvethe humidity conditions of the wall increasing the evaporation rate. In this caseit is important to point out that due to a)the irregular shape of the stone useoutside in the construction of the wall, and b)the possible use of renders,covering this kind of stonework, that systematically has been remove in modernrestorations, even if in this wall it hasn't been proved at the moment, the use ofa lime render outside would improved substantially the moisture content of thewall by increasing the evaporation surface.

Even if one may think that rising damp in the south facade can be more severerespect the north one, due to subsoil structure, and could originate by capillary ahigher humidity level, the use of cement mortars have undoubtedly contributedto a progressive increase of RH% in those walls, that cannot evaporate to theexterior due to the impervious characteristics of the mortars used. Other studieshave also showed the disadvantaged of the low porosity of cement mortarsconsisting of very small pores sizes, which hinder water movement in themasonry, Peroni et al.7, Torraca 8. This characteristic that might seem positiveby reducing penetration of rainwater ends up by causing damage because ofaccumulation of moisture behind cement joints that do not allow evaporation. Infact, it has also been observed some cracks in the mortar type I, due to its



elasticity modulo value, which can even let water get inside, increasingprogressively walls moisture contents.

4. Conclusion.

According to our preliminary results, and other literature reports, we believethat cement mortars should be avoided in mortar mixtures for restoration worksand that the use of lime based mortars should be restored due to their optimalprotective properties, absorbing themselves weather stress and protectinghistoric walls from deterioration. In conclusion, from our studies and personalexperiences we highly recommend the preservation of traditional protectiverenders, where they appeared originally, and the use of lime mortar in themaintenance of the joints in order to protect and avoid premature deterioration.

5. Acknowledgement.

This study is part of the PHD tesis of the first author, and has been carried outunder grant XUGA 11601A95, in agreement with the actual "Direccion Xeraldo Patrimonio Historico e Documental" of Conselleria de Cultura, Xunta deGalicia, Spain. A special thank to "Servicios Generates de Apoyo a laInvestigation", Universidad de A Coruna, for their help.

References.

1. Luengo y Martinez. La iglesia del Monasterio de San Antolin de Toques.Coruna, paraiso del turismo. 1977

2. IGME. Mapa geologico de Espana. E. 1: 50.000. Arzua. Servicio depublicaciones del Ministerio de Industria.

3. Riegl, A. El culto moderno a los edificios. Col.La balsa de la medusa. Visor1987.

4. Iglesias Martinez, M. C. Modern interventions on the traditional limemortars of historic walls: cause of biologic deterioration of GalicianArquitectural heritage's mural paintings, pp 35-36. Actas of the IIIInternational symposium on biodeterioration and biodegradation. Santiagode Compostela, Spain. 1996.

5. Massari G. &I. Damp buildings old and new. ICCROM. Rome 1993.6. Teutonico J.M. et al. Smeaton project:factors affecting the properties of lime

based mortars. Bulletin of the Association for the Preservation Technology(APT). Vol.25, N°3-4, Albany.Sept.1994.

7. Peroni et al. Lime based mortars for the repair of ancient masonry andpossible substitutes. Mortars, Cements and Grouts used in the conservationof historic buildings. Symposium 3-6.1981. Rome.


rectangular apse or presbytery covered with a barrel vault. (fig.l). · 2014-05-20 · rectangular...

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