Climate change, Climate change, ‘‘greeninggreening’’ of ofmasonry and implications formasonry and implications for

the decay of built heritagethe decay of built heritageand new buildand new build

Prof. B.J. Smith, Dr H.A Viles,Dr N.L. Betts, Dr J.J. McAlister,

Prof. P.A.M. Basheer,Prof A.S. Whiteley

Climate Change and Stone Decay:Climate Change and Stone Decay:A UK PerspectiveA UK Perspective

Many presumptions regarding salt-inducedMany presumptions regarding salt-induceddecay in the UK come from studies ofdecay in the UK come from studies oflimestones limestones in the comparatively dry southeastin the comparatively dry southeast

Explanations and preferred conservationExplanations and preferred conservationstrategies are based upon similar, stablestrategies are based upon similar, stableconditions and responses prevailing across theconditions and responses prevailing across therest of the UKrest of the UK

Sandstone Decay by Salt ActionSandstone Decay by Salt Action

Premised on periodic wetting followed by thorough dryingPremised on periodic wetting followed by thorough drying

Shallow wetting related to migration of a Shallow wetting related to migration of a ‘‘wetting frontwetting front’’

Wetting/drying facilitates surface and near-surface saltWetting/drying facilitates surface and near-surface saltaccumulation depending on drying rateaccumulation depending on drying rate

Leads to granular Leads to granular disaggregation disaggregation and/or contourand/or contourscalingscaling

Assumptions have influenced the design of standardAssumptions have influenced the design of standarddurability testsdurability tests

ContourContourScalingScalingandandGypsumGypsum

Climate Change and the Northwest UKClimate Change and the Northwest UK

Rainfall consistently increases in total amount and frequency towards theRainfall consistently increases in total amount and frequency towards thenorthwest northwest –– Belfast c. 200 rain days per annum Belfast c. 200 rain days per annum

Future scenarios for the northwest predict significant changeFuture scenarios for the northwest predict significant change

Increased uncertainty in day-to-day weather conditionsIncreased uncertainty in day-to-day weather conditions

Wetter, warmer and longer wintersWetter, warmer and longer winters

Could suggest increased time-of-wetness for exposed stoneworkCould suggest increased time-of-wetness for exposed stonework

Could result in increased chemical weathering of stonework in theCould result in increased chemical weathering of stonework in thenorthwest (northwest (Viles Viles 2002)2002)

Dryer conditions in the southeast of the UK could increase the significanceDryer conditions in the southeast of the UK could increase the significanceof salt crystallisation (of salt crystallisation (Viles Viles 2002)2002)

Predicted Rainfall ChangePredicted Rainfall Changefor the British Islesfor the British Isles

Source: Fealy and Sweeney, 2007

Regional Climate Change Scenarios: Temperature

Source: Fealy and Sweeney,2007

Regional Climate Change Scenarios: Rainfall

Climate Change ImplicationsClimate Change Implicationsfor Stoneworkfor Stonework

Prolonged and presumably more deeply penetratingProlonged and presumably more deeply penetratingwinter wetness alters a major control on stone decaywinter wetness alters a major control on stone decayprocessesprocesses

Should affect salt penetration and zones of concentrationShould affect salt penetration and zones of concentration

Could influence patterns of biological colonisation,Could influence patterns of biological colonisation,especially if wetness is combined with warmth and theespecially if wetness is combined with warmth and theabsence of frostabsence of frost

History of Atmospheric Pollution andHistory of Atmospheric Pollution andStone Decay in Belfast: Origins of theStone Decay in Belfast: Origins of theprojectproject

High concentrations of sulphates, particulates and marine aerosolsHigh concentrations of sulphates, particulates and marine aerosols

Predominance of building sandstonesPredominance of building sandstones

Rapid soiling of new and replacement stoneRapid soiling of new and replacement stone

Frequent surface Frequent surface disaggregation disaggregation and contour scaling of sandstonesand contour scaling of sandstones

Widespread formation of Widespread formation of indurated indurated iron coatingsiron coatings

History of ill-thought-out interventionHistory of ill-thought-out intervention

Anecdotal evidence of increased Anecdotal evidence of increased ‘‘greeninggreening’’ of buildings, independent of of buildings, independent ofinterventionintervention

Pollution overPollution overBelfastBelfast

Soiling: SevenSoiling: SevenYears afterYears afterCleaningCleaning

AnecdotalAnecdotalevidence forevidence forincreasedincreasedgreening ofgreening ofsandstonesandstone

St MarkSt Mark’’s Church, Belfasts Church, BelfastMay 1999 & October 2001May 1999 & October 2001

RESEARCH FINDINGSRESEARCH FINDINGSExposure Trials 1:Exposure Trials 1:Late 1980s, Early 1990sLate 1980s, Early 1990s

Number of exposure sites across BelfastNumber of exposure sites across Belfast

Rapid growth of gypsum crusts on shelteredRapid growth of gypsum crusts on shelteredsamplessamples

Samples exposed to Samples exposed to rainwashrainwash, crust-free, crust-free

SHELTERED PORTLAND:SHELTERED PORTLAND:Belfast - 1 yearBelfast - 1 year

SHELTERED PORTLAND:SHELTERED PORTLAND:Belfast - 1 yearBelfast - 1 year

RESEARCH FINDINGSRESEARCH FINDINGSExposure Trials 2:Exposure Trials 2:Late 1990sLate 1990s

Trials repeated at same sites as 10 years previouslyTrials repeated at same sites as 10 years previously

Continued gypsum crust development on sheltered samples -Continued gypsum crust development on sheltered samples -possibly less rapidpossibly less rapid

Extensive biological colonisation of Extensive biological colonisation of rainwashed rainwashed samplessamples

Marked reduction in permeability associated with colonisationMarked reduction in permeability associated with colonisation

Coincided with period of above normal rainfall amount andCoincided with period of above normal rainfall amount andfrequency during winter monthsfrequency during winter months

Exposure Trial: City HallExposure Trial: City Hall

Microbial Community on Microbial Community on DunhouseDunhouseSandstone Exposed at Belfast Sandstone Exposed at Belfast HarbourHarbourfor 2 yearsfor 2 years

Fungal Fungal Hyphae Hyphae and Algal Cells/Filamentsand Algal Cells/Filamentson Dumfries Sandstone Exposed aton Dumfries Sandstone Exposed atNorth Belfast for 2 yearsNorth Belfast for 2 years

Mucilage Binding Coal Mucilage Binding Coal Flyash Flyash totoDunhouse Dunhouse Sandstone Exposed atSandstone Exposed atBelfast Belfast Harbour Harbour for 2 yearsfor 2 years

Reduction in Permeability due to BiologicalReduction in Permeability due to BiologicalColonisationColonisation, , Dunhouse Dunhouse SandstoneSandstoneExposed at Belfast Exposed at Belfast Harbour Harbour for 2 yearsfor 2 years

Rainfall Patterns for Exposure TrialRainfall Patterns for Exposure Trial

RESEARCH FINDINGSRESEARCH FINDINGSSalt Related Decay 1:Salt Related Decay 1:St MatthewSt Matthew’’s Churchs Church

Extreme decay of quartz sandstone in the low-lying, pollutedExtreme decay of quartz sandstone in the low-lying, polluteddocks area of Belfastdocks area of Belfast

Characterised by rapid retreat of individual blocksCharacterised by rapid retreat of individual blocks

The need for site-specific conservation identifiedThe need for site-specific conservation identified

Research into the diagnosis of decay processes and controlsResearch into the diagnosis of decay processes and controlsrequiredrequired

Removal of complete blocks of sandstone permittedRemoval of complete blocks of sandstone permitted

Rapid RetreatRapid Retreatof Individualof IndividualBlocksBlocks

RESEARCH FINDINGSRESEARCH FINDINGSSalt Related Decay 2:Salt Related Decay 2:Results from AnalysesResults from Analyses

Two- and three-dimensional salt distributions by within completeTwo- and three-dimensional salt distributions by within completeblocks by IC and AASblocks by IC and AAS

Gypsum concentration in the near surface zone linked to contourGypsum concentration in the near surface zone linked to contourscalingscaling

Sodium, Magnesium and Chloride distributed throughout blocks, butSodium, Magnesium and Chloride distributed throughout blocks, butconcentrated in concentrated in ‘‘hot spotshot spots’’

Lack of correlation between Sodium, Magnesium and Chloride mightLack of correlation between Sodium, Magnesium and Chloride mightimply imply ‘‘saltsalt’’ dispersion by ion diffusion dispersion by ion diffusion

Ion diffusion may have implications for other alteration processes,Ion diffusion may have implications for other alteration processes,including iron migrationincluding iron migration

Gypsum Distribution withGypsum Distribution withDepthDepth

NaNa++ Mg Mg++++ & & ClCl-- DistributionDistributionwith Depthwith Depth

RESEARCH FINDINGSRESEARCH FINDINGSSalt Related Decay 3:Salt Related Decay 3:Experimental ResultsExperimental Results

Modelling block retreat: the importance ofModelling block retreat: the importance ofof deep saltsof deep salts

Assessing the feasibility of ion diffusionAssessing the feasibility of ion diffusion

Salt andSalt andMoisture FlowsMoisture Flows

Decay Patterns & SurfaceDecay Patterns & SurfaceChemistryChemistry

DiffusionDiffusionCoefficientCoefficient

SUMMARY 1SUMMARY 1Possible Changes in the Nature ofPossible Changes in the Nature ofSalt-Related Stone DecaySalt-Related Stone Decay

Prolonged saturation of complete stone blocksProlonged saturation of complete stone blocks

Irregular and possibly incomplete surface drying for much of yearIrregular and possibly incomplete surface drying for much of year

Deeper penetration of salts (especially those of high mobility)Deeper penetration of salts (especially those of high mobility)

Movement of salt through stone by ion diffusion rather than in solutionMovement of salt through stone by ion diffusion rather than in solution

Presence of a store of Presence of a store of ‘‘deep salt' that may facilitate continued retreat ofdeep salt' that may facilitate continued retreat ofindividual blocks following initial individual blocks following initial delamination delamination or removal of surface layersor removal of surface layersduring conservationduring conservation

Visual Visual disamenitydisamenity

SUMMARY 2SUMMARY 2Possible Effects of Increased BiologicalPossible Effects of Increased BiologicalColonisation of Rainwashed StoneworkColonisation of Rainwashed Stonework

Active biological decay, both chemical and physicalActive biological decay, both chemical and physical

Decrease in surface porosity/permeabilityDecrease in surface porosity/permeability

Continued wetting of stone by frequent rainfall andContinued wetting of stone by frequent rainfall andcondensationcondensation

Prolonged saturation following reduced evaporationProlonged saturation following reduced evaporation

Facilitation of dust deposition and the formation of complexFacilitation of dust deposition and the formation of complexbio-mineralogic bio-mineralogic crustscrusts

Implications for Stone ConservationImplications for Stone Conservation

Avoid actions that further promote biological colonisation:Avoid actions that further promote biological colonisation: Chemical cleaningChemical cleaning Increased atmospheric nitrogenIncreased atmospheric nitrogen

Need to appreciate changing patterns of soiling:Need to appreciate changing patterns of soiling: Greening of exposed surfaces instead of gypsum crusts in sheltered areasGreening of exposed surfaces instead of gypsum crusts in sheltered areas

Avoid ad hoc interventionAvoid ad hoc intervention

Surface dressing alone may activate deep saltsSurface dressing alone may activate deep salts

Consider alternative intervention:Consider alternative intervention: BiocidesBiocides Water repellentsWater repellents Requires new protocols for application in a Requires new protocols for application in a ‘‘wetter worldwetter world’’

Greening after ChemicalGreening after ChemicalCleaningCleaning

AggressiveAggressiveCleaning ofCleaning ofGreenedGreenedStoneworkStonework

April 2002

June 2002

Test WallTest WallSt MatthewSt Matthew’’ssChurchChurch

Test Wall after 4 monthsTest Wall after 4 months

Treated and UntreatedTreated and UntreatedTest WallTest Wall

CONCLUSIONSCONCLUSIONS

The high rainfall totals and rainfall frequency in Belfast provide an insight intoThe high rainfall totals and rainfall frequency in Belfast provide an insight intothe possible consequences of increased time-of-wetness for stoneworkthe possible consequences of increased time-of-wetness for stonework

Research has suggested the need to rethink assumptions concerningResearch has suggested the need to rethink assumptions concerningpatterns and controls on salt related decay in patterns and controls on salt related decay in ‘‘wetwet’’ environments environments

Stone response to increased time-ofStone response to increased time-of––wetness is complex, with manywetness is complex, with manyfeedbacks operating. The effects of which are complicated by changingfeedbacks operating. The effects of which are complicated by changingpollution regimes: less pollution regimes: less suplhursuplhur, increased localised nitrogen, different, increased localised nitrogen, differentparticulatesparticulates

Conservators should assess alternative approaches to building management,Conservators should assess alternative approaches to building management,including a more flexible approach to preventative strategiesincluding a more flexible approach to preventative strategies

The New ProjectThe New Project

Aim The overall aim is to understand how periods

of prolonged, deep-seated wetness impact onthe ‘greening’, deterioration and potentialconservation of sandstone masonry, throughan interdisciplinary study linking civilengineering, geomorphology, climatology andenvironmental microbiology with architectsand conservators.

Objectives 1Objectives 1

1. To understand the current greening of sandstone walls typical ofthat found across the NW UK today and its relationship to climate, airquality and micro-environmental conditions. (Smith, McAlister andViles)

2. To monitor the moisture contents of sandstone test walls to quantify‘time of wetness’ (both at the surface and at depth) in the west ofNorthern Ireland and its relationship to greening. (Basheer & Viles)

3. To relate wetness regimes in sandstone walls to existing climaticconditions. (Basheer, Betts & Smith)

4. To determine future wetness regimes in sandstone walls throughstatistically downscaling climate projections and utilising links betweenwetness and climatic parameters discovered in objective 3. (Smith &Betts)

Objectives 2Objectives 2

5. To investigate the relationship between moisture levels and iondiffusion of key anions and cations within sandstone blocks and theirpotential significance for sandstone deterioration. (McAlister andBasheer)

6. To investigate the links between greening (algal colonisation) ofsandstone blocks and moisture regimes and deterioration and todevelop and test new conceptual models of sandstone deterioration

under wetter, ‘greener’ conditions. (Viles, Smith and Whiteley) 7. To devise practical advice for building with sandstone and

managing the greening and deterioration of existing sandstone wallsunder wet conditions. (Smith, Basheer, Betts, McAlister, Viles &Whiteley)

Programme stagesProgramme stages

PROGRAMME STAGE 1: Field survey and sampling of sandstone walls,Belfast (Objective 1)

PROGRAMME STAGE 2: Construction and monitoring of test walls nearEnniskillen (Objectives 1-3)

PROGRAMME STAGE 3: Laboratory simulation of algal colonisation and itsimpact on moisture regimes and sandstone deterioration (Objective 6)

POGRAMME STAGE 4: Laboratory simulation of ion diffusion withinsandstone blocks under saturated conditions and its impact on sandstonedeterioration (Objective 5)

PROGRAMME STAGE 5: Linking current climate to moisture regimeswithin sandstone masonry walls and predicting future conditions(Objectives 3 and 4)

PROGRAMME STAGE 6: Developing practical guidance and advice forfuture use and management of sandstone masonry in NW UK (Objective 7)