International Journal of Sustainable Built Environment (2013) 2, 65–72

Gulf Organisation for Research and Development

International Journal of Sustainable Built Environment

ScienceDirectwww.sciencedirect.com

Perception of darkening of stone fac�ades and the need for cleaning

Iqbal Marie ⇑

Department of Civil Engineering, Faculty of Engineering, The Hashemite University, Jordan

Received 11 May 2013; accepted 24 September 2013

Abstract

This study intends to understand and analyse the visual pollution caused by particle deposition on the stone fac�ades that ultimatelycause blackening of buildings and affect the aesthetic value of the fac�ade. The aesthetics is complex and is subjected to differences inopinion between individuals. For the purpose of this study different types of buildings in Amman (residential, commercial, historicaland others); have been randomly selected and visually studied by investigating public perceptions of the aesthetic benefits, and valueof stone cleaning. An interaction chart relating the darkness level, the deposition patterns and the type of building has been developedin order to assess the priority given by the public to stone fac�ade cleaning decision.

Keywords: Stone fac�ade; Blackening; Visual pollution; Stone cleaning

� 2014 The Gulf Organisation for Research and Development. Production and hosting by Elsevier B.V.Open access under CC BY-NC-ND license.

1. Introduction

The main phases in the life cycle of a building are:design, construction and operation or service phase. Theduration of the design and construction phases does notexceed 5% of the building life span, while the operationphase represents 95% of the life time of a building. Theenvironmental performances of building components dur-ing its lifetime for any phase can be related to both singlecomponent and whole building. This study focalizes onlyon the eco-efficient interrelations between stone buildingfac�ades as a main external component of a building and

2212-6090 � 2014 The Gulf Organisation for Research and Development. Prod

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the society in terms of aesthetical point of view duringthe service phase of the life cycle.

Natural stone has been widely used as an exterior clad-ding of fac�ades in Amman. It is one of its main character-istics that serve aesthetic purposes by variations in textureand patterns giving it its unique homogeneous character. Awide range of stone patterns used throughout the cityreflects the individual style preferences of the owner of abuilding, the architect or both. Several textural varietiescan be tooled and used on building fac�ades. Some of thenames given to the type of texture are local Arabic terms:The most famous textures are:

(1) Tubzeh: A roughly dressed surface done by havingrelatively thick stone with a portion of about 5 cmfrom the surface. Small pieces are then split orchipped out from the surface with a pitching tool.

(2) Mufajjar: A medium dressing which is done with apoint chisel hammered on the stone surface withsingle strokes, creating a speckled surface.

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66 I. Marie / International Journal of Sustainable Built Environment 2 (2013) 65–72

(3) Musamsam: A series of short, fine parallel linedressings done with a tooth chisel.

(4) Polished: (Flat) either smoothly polished surfacethat can be achieved with special polishingmachines or a roughly polished surface that canbe achieved through sand blasting.

Many other types have been well documented by MayShaer, in a study which investigates the use of stone inAmman providing a compilation of building surface pat-terns composed of stone in various designs. Fig. 1 showssome types of textures.

Limestone is a natural material that is most quarriedand used in Jordan. The quality of the stone depends onits hardness, purity, and porosity.

After construction, a building might be thought of ashaving certain initial aesthetic qualities. Building fac�adespass through cycles of change in colouring due to the accu-mulation of soiling. Different fac�ade designs and stonetypes perform differently over-time and therefore may soilat different rates. After a number of years with the accumu-lation of soil, the aesthetic value declines as soilingincreases. Grossi et al. (2003) found that limestone exhibitsa soiling proportional to the square root of the time ofexposure which indicates frequent cleaning requirements.The speed of soiling varies considerably as building materi-als vary in their vulnerability to the uncontrollable influ-ence of weathering, although as all materials eventuallychange in appearance, stone fac�ades are no different in thatmanner. Discolouration in rendered fac�ades occurs veryfrequently due to various reasons such as carbonation, cor-rosion, cracking, dirt deposition, biological colonizationand others (Flores-Colen et al., 2008). The most commonexample of colour change on building exteriors is blacken-ing, which is considered as aesthetic degradation that hasimportant social consequences in terms of the visual per-ception of any building. Some types of stains, in conjunc-tion with the presence of water, contribute to the physicaldegradation of the cladding (Prieto et al., 2007). The sur-face flow of water down to the fac�ade producing stainswas studied and its effect related to some common designfeatures on buildings (Chew and Tan, 2003).

The blackened surfaces create a visual nuisance. Theaesthetic degradation has been generally less researched

Tubzeh Mufajje

Fig. 1. Texture of some building’s ston

in studies than the chemical and physical impact of pollu-tants on building surfaces. Blackening of light colouredsurfaces eventually reaches a point where it becomes aes-thetically unacceptable. As visual pollution is an aestheticissue, referring to the impacts of pollution that impair one’sability to enjoy a view (Stapleton, 2004), the blackened sur-faces affect the aesthetics of the fac�ade and often offendsviewers’ eyes causing visual pollution. Moreover visualamenity and visual pollution can be defined by the levelof common satisfaction. This satisfaction depends on theentirety of the criteria of the scene components. These cri-teria are associated with the mental process concerned withthe organized meaning of location, formation, conditionand relationship (Bakhotmah, 1998). Therefore the visualeffect of the soiled fac�ades is subjected to differences inopinion amongst individuals based upon their own aes-thetic senses, expectations and experiences. The accumula-tion of contaminants on buildings is not necessarily evenlyspread out but producing different patterns. Differentblackening patterns on buildings create different levels ofacceptability and could be relevant to a decision aboutcleaning (Grossi et al., 2003). Cleaning buildings’ fac�adeswill improve the appearance of the street scene giving ahealthy visual environment which promotes the values ofliving people in that community. Therefore desirability offac�ade cleaning can be for aesthetic reasons, for the protec-tion of the building from degradation, or both.

Regulating procedures for self diagnosis and a stringentapplication of periodic cleaning of fac�ades is required for acity like Amman. These methodologies must be developedaccording to a set of procedures with a logical sequence inorder to adopt a proper solution (Flores-Colen et al.,2008).

Despite the fact that this study discusses the require-ments of fac�ade cleaning in order to lighten and bringclearance and beauty to fac�ade for aesthetic reasons, fac�-ade cleaning is essential for architect or conservator toexplore problems and failure triggers, and help to analysethem to take protective measures and maintain the buildingeffectively (Grimmer and Clean, 1988). Heavy soiling inparticular can easily conceal structural defects such as dete-riorated areas, local fractures or even major structuralcracks (Andrew, 1994). Much is normally revealed aboutthe masonry condition by removal of soiling deposits.

Musamsam Flat

e fac�ades in Jordan (Shaer, 2000).

I. Marie / International Journal of Sustainable Built Environment 2 (2013) 65–72 67

When soiling is removed, the appealing stone colour will beuncovered, leading to an increase in the attractiveness of abuilding. Therefore a cleaning life cycle should be plannedprior to cleaning works, providing a useful tool for thedecision maker (Espinoza et al., 2012).

Grossi et al. (2003) studied the soiling rate of severalbuilding stones when exposed to different urban environ-ments and conditions of exposure. Accordingly the possiblecleaning time intervals to maintain aesthetic requirementsand to prevent stone degradation were estimated. Differentmethods of cleaning are appropriate for different buildings,depending on the design, quality, condition, building meth-ods and design characteristics of individual fac�ades and, ofcourse, on the nature, distribution and amount of the soil-ing. Cleaning of fac�ades can be undertaken for aestheticreasons or for the protection of the building, or both. Ifthe cleaning method has been chosen and carried out cor-rectly, a cleaned fac�ade should be expected to stay quiteclean for decades, depending on the surface texture ofstones, the projected architectural detailing, local environ-ment pollution elements, and atmospheric conditions.

Selecting the method of cleaning is very essential anddepends on the type of fac�ade and building in addition tomany other ecological considerations. As a practical pre-caution to control the staining of a fac�ade by dirt carriedin the atmosphere, it may be appropriate to undertake reg-ular and thorough washing of the fac�ade with low pressurewater, concentrating on the parts not exposed to the rain,and making sure that the dust or other loose dirt is washeddown and away from the building and not deposited onlower parts of the fac�ade (Flores-Colen et al., 2008).

The most evident direct cost associated with soiling isthe cleaning of the building fac�ade. However, increased fre-quency of cleaning or repainting of soiled surfaces becomesa significant economic cost (Watt et al., 2008). In fact inAmman, cleaning of building fac�ades is mainly based onan unplanned decision of the owner. Many factors mayaffect that decision as, insufficient budgeting for intensiveand systematic cleaning; insufficient knowledge of fac�ade

b

d e

a

Fig. 2. Different buildings in Amman with d

cleaning benefits; and a lack of eco-friendly cleaning tech-nique to support planning actions, in this domain. Howoften will the building require cleaning? And what is thebest cleaning technique to be employed? It is a matter ofmany considerations of economic and public attitudes(Watt et al., 2008). The decision-taking for full or partialfac�ade cleaning or even non-cleaning is also of considerableissue. The cleaning of a specific area within an individualbuilding’s fac�ade breaks the unity of the fac�ade and dis-rupts the architectural context of a street. Similarly, clean-ing the entire fac�ade using different cleaning methods atdifferent times will cause difficulty in matching the colourof each area within the whole. Thus, the time of cleaningand the procedure carried out are mostly required in termsof areas rather than buildings (Swann, 2013).

This research intends to study the relationship betweensoiling and blackening of building stone fac�ades, perceivedcolour and aesthetic acceptability at a range of differentbuilding types. Fig. 2 represents different visible results ofheavy soiling processes on different buildings located inAmman but is not restricted to these causing a negativeimpact on the environment by altering the natural colourof stones, thus possibly obscuring any ornamental designsand affecting the appearance of a building. The extent ofsoiling present on stone buildings was a criterion by whichperceived judgments about those buildings are made, withthat impact existing within a wider aesthetic framework(Grimmer and Clean, 1988). Christopher Andrew (1994)developed a theoretical model of the relationship betweensoiling, building complexity and aesthetics.

The major point of this work is to create a methodwhich assists people and professionals in appraising the vis-ible built environment by dealing mainly with two vari-ables, one is the humanistic and the other is the builtenvironment complexity. The humanistic is the visual emo-tion and preferences of the people while the built environ-ment complexity involves the blackening of stone fac�adeparameters that have impact on the aesthetic value of abuilding fac�ade. The obtained method may assist the

c

f

ifferent levels and patterns of darkening.

Fig. 3. Biological colonization deposits.

Fig. 4. Stone fac�ades overlaid with a grid for calculating the level ofdarkening.

1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5

Uniform Horizontal Vertical Irregular

Pattern of deposits on the stone facades

Building Types: 1. Commercial 2. Religious3. Archeological4. Historical5. Residential

a. on main street b. on secondary street

Partial cleaning No cleaning Full cleaning

Fig. 5. Specific visual format matrix to record the interviewed people’sopinions.

68 I. Marie / International Journal of Sustainable Built Environment 2 (2013) 65–72

fac�ade cleaning decision-making to be done by responsiblepersonnel to preserve the aesthetic value of a building.

2. Methodology

To verify the visual impact of staining patterns on stonefac�ades in the Amman city and assessing the aestheticalappearance of buildings, interviews were conducted duringa period of three months, beginning June ending August ofyear 2010. A sample of 100 survey respondents participatedin this study for each randomly selected building. The 100interviewees do not have to be the same for all buildings.As the pattern of soiling on buildings’ fac�ades proved tobe an important factor that might influence the acceptabil-ity of soling on buildings (Grossi and Brimblecombe,2004), the deposits’ pattern type for certain well classifiedbuilding type is taken as a main category in this study.Consequently the interviewed persons’ opinions have beencollected face to face. The respondents report on what theyvisually feel about the requirements for cleaning in relationto the contaminated building fac�ades. A single questionwas used to investigate if the building wants fac�ade clean-ing or not. It is: “Do you think this building requires fullcleaning, partial cleaning or no cleaning for the benefit ofatheistic appearance of the fac�ade?” A picture has beentaken for each building used in the interview using a digitalcamera. Adobe Photoshop software has been used for eachdigital image to estimate approximately the percentage ofthe contaminated area with respect to the whole fac�adeof the building by overlaying it with a grid. This percentagevalue is recorded as the level or degree of darkening. Asample of one of the images is shown in Fig. 4. After thefieldwork has been completed and each building image isanalysed, the data are organized and grouped in a preparedvisual matrix device as shown in Fig. 5 to aid categorizingdata.The main factors that contribute to the stone fac�adescleaning requirement are:

a. Degree of the darkness of the colour of soiling – greyto black or dark brown deposits of dust or unknownstains. The scale of darkening is of values with a

range from the best condition of level 0 with absenceof visible dark deposits to the worst of level 100 withsevere blackening condition.

b. Pattern of deposits are as shown in Figs. 2 and 3:(1) uniform;(2) irregular deposits;(3) vertical streaks;(4) horizontally spread deposits;(5) any mixed patterns with/without biologi-

cal colonization.c. Types of buildings: the buildings studied in this

research are divided into four main groups:(1) Commercial buildings.

I. Marie / International Journal of Sustainable Built Environment 2 (2013) 65–72 69

(2) Residential buildings which have been dividedinto two classes: Class-a residential buildingswhich are located on main streets whilst Class-bresidential buildings are located on secondarystreets.

(3) Religious buildings.(4) Historical buildings.(5) Archaeological.

Most of the selected buildings have the Tubzeh, Musam-sam, flat or the Mufajjar surface dressing texture.

The extents of cleaning intervention required are classi-fied into three categories:

� No cleaning: a fac�ade in this condition does notrequire any cleaning at this stage and it has anaccepted appearance.

Table 1Sample of the selected buildings and the opinion of 90% of the people who h

Building Streaks pattern

Irregular streaks

Vertical streaks

Uniform

Vertical streaks

� Partial cleaning: a fac�ade is in a condition whichrequires only localized cleaning.

� Full cleaning: serious contamination affecting theappearance of the fac�ade which requires wide spreadcleaning.

Table 1 represents a sample of the selected buildings andthe opinion of 90% of the people who have been inter-viewed for cleaning requirements.

A visual representation of the relationship betweenvariables is carefully designed representing theinterviewed individual’s reflection and interaction to beappropriately used as a short path to gaining insightsinto a building’s fac�ade cleaning requirements.These requirements are assessed into three different catego-ries, ranging from no cleaning, partial cleaning to fullcleaning.

ave been interviewed for cleaning requirements.

Building type Cleaning requirements

Residential building Full cleaning

Religious building Partial cleaning

Commercial Full cleaning

Commercial Full cleaning

(%)

Fig. 7. Respondent decision about full cleaning requirements for all typesof buildings with irregular dark deposits for different darkness levels.

70 I. Marie / International Journal of Sustainable Built Environment 2 (2013) 65–72

3. Results

For all the fac�ades of the randomly selected buildings,three types of discolouration affect more than 50% offac�ades: vertical streaks, irregular, and uniform soiling.

The relationship between soiling, architecture and aes-thetics is complex and is subjected to differences in opinionbetween individuals. Individuals respond differently totheir environment, based upon their own aesthetic sensesand experiences.

The data collected are plotted for each building type andsoiling pattern according to the cleaning requirements deci-sion (full, partial or no cleaning). Fig. 6 shows the relationbetween the darkness level and the percentage of respon-dents for a residential building of type (a) with irregulartype of darkening. It is clear that a darkness level of lessthan 50 does not affect the aesthetical value of the fac�adeand therefore no cleaning is required, while a darkness oflevel above 75 requires full cleaning supported by morethan 45% of the interviewees. The data for all buildingtypes are plotted to give an indication about the visualimpression of darkness on the society.

Data representing the interviewees’ decision about fullcleaning requirements for all types of buildings with irreg-ular dark deposits of different darkness levels are shown inFig. 7. It is clear that soiling of building fac�ades acceptanceby the people is related to the type of building. It is shownthat the archaeological and historical buildings are the leastaffected aesthetically by soiling irrespective of the darknesslevel, while the commercial buildings are greatly affected bythe appearance of the external fac�ade.

The final layout of the cleaning decision-making dia-gram of the chart in Fig. 8 has been reached by first prepar-ing concentric circles on a grid with the x-axis representingthe level of darkness whilst the y-axis representing the pat-tern of the dark deposits. The concentric circles of centres(0, 0) (0,0) are the track of points with a certain darkness

Res

pond

ents

opi

nion

( %

)

Darkness Level

Residential Building Façade with Irregular Streaks

Fig. 6. Relation between the respondent opinions about cleaningrequirements and the darkness level for irregular streaks on residentialbuildings’ stone facades.

Fig. 8. Cleaning decision interaction diagram.

level and pattern. By trial and error lines of certain slopesare positioned on the grid. These lines are selected to satisfycleaning requirements for each type of building fac�ade asindicated by Figs. 6 and 7 and other similar charts for dif-ferent soiling patterns.

The intersection of the circles with the lines may quan-tify the visual impact of the building fac�ade through acleaning requirement indicator.

I. Marie / International Journal of Sustainable Built Environment 2 (2013) 65–72 71

The main viewers’ comments that are reflected on thedesigned cleaning decision diagram can be summarized as:

(1) Some viewers considered the cleaning of archaeo-logical or historic buildings not acceptable due tothe resulting false impression about its age andtherefore losing its archaeological value. Thus,cleaning historic masonry is recommended onlywhen necessary to halt deterioration or to removeheavy soiling, and only after careful testing usingthe gentlest cleaning means possible (Grimmerand Clean, 1988).

(2) Most of the soiling patterns on the fac�ades of com-mercial buildings are considered visually lessacceptable with a negative impact on the customersand employees compared to other types of build-ings, therefore requiring regular cleaning.

(3) Religious buildings are seen as having the secondpriority for cleaning after commercial buildings.

To verify the applicability of the diagram in Fig. 8 as astone facade cleaning activity decision-making interactiondiagram, a commercial building is considered with a 60%darkening level of vertical streak deposits represented bypoint (a) located on one of the circles. Then the intersectionof this circle with the line for the commercial building isreflected on the cleaning requirement indicator. Accord-ingly the building fac�ade requires full cleaning.

When the decision of cleaning the fac�ade is made, theaesthetic expectations must be proficiently managed forbest outcomes of the various available cleaning methods.Following the majority, the visible environment will abso-lutely become much better physically as well as visually(Bakhotmah, 1998). The cleaning date and procedureshould be documented for future reference and assessmentof buildings’ fac�ades. To assess and evaluate the progresstowards more sustainable systems, it is essential thatproper monitoring of the environmental and social impactsis done on a regular basis and that the results are used tohelp to focus societal attention on ways to make furtherimprovements towards sustainable societal lifestyles(Klemes et al., 2012).

In areas where soiling is shown to be aesthetically detri-mental, a cleaning policy should be developed in relation tothe wider urban context of the building. The cleaning ofindividual buildings in fac�ades should be discouraged.Cleaning of fac�ades for different adjacent buildings shouldtake place at one time using a uniform method.

4. Conclusion

Visual pollution due to contaminated stone fac�ades is anaesthetic concern that impairs the ability of people to enjoythe built environment. The developed cleaning decision-making interaction diagram involves the identification ofcontamination patterns and its degree of colouration inrelation to the type of the building, therefore providing

an integrated visual tool to assist building owners, ordecision-makers in assessing building fac�ade cleaningrequirement. That may be the first step towards the predic-tion of optimal cleaning procedure and technique.

Further policy developments at a local government levelare necessary to establish guidelines for technical cleaningactions and produce specific schedule to ensure that clean-ing responses are handled accordingly.The following goalscan be achieved:

(1) Find an adequate tool to quantify the respondingtowards visual pollution due to contaminated stonefac�ades that have an impact on the built environ-mental appearance.

(2) Suggest a decision-making tool for solving a visualpollution problem rather than describing it.

(3) Propose a pre-decision chart to evaluate the visibleacceptance level of stone fac�ades for different typesof buildings in order to assess their appearance onthe scale of aesthetics before a conservationdecision.

5. Further research

Further collaborations and studies are required toenhance the cleaning decision interaction diagram takinginto consideration the cleaning process and accordinglystudy the required improvements that should be made toimprove the tools and to incorporate the findings by pol-icy-makers in real progress towards truly sustainable fac�-ade cleaning process.

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