What’s the Point? 2: Lime finishes in a changing climate symposium

In the current debates over (re)application of external lime finishes to historic stone-built structures in Scotland, physical evidence and documentary record still faces dismissal by proponents of the bare stone dogma advanced by John Ruskin.

Ruskin’s aesthetic morality, especially his insistence on respect for the nature of the material – his ‘lamp of truth’ where stone was involved – stimulated a fashion in Scotland for scraping away both internal and external wall finishes to expose what was believed by a new generation of architects in the second half of the 19th century to be the ‘original’ and ‘honest vernacular’ appearance of its late medieval and renaissance secular and ecclesiastical architecture. 

In an architectural tradition that evolved through the depths of the ‘little ice age’, weatherproofing, especially defence against penetration of water through porous sandstone, meant the external rendering of most high-status stone buildings.

In this paper, Richard examines the impact of that bare stone aesthetic in shaping modern perceptions of Scotland’s late medieval and renaissance architectural heritage. It challenges the vision of a land of exposed stonework and primitivism, drawing on surviving physical evidence and exploring also the visual record for external surface finishes on both gentry and greater noble houses in Highland and Lowland districts.

Its main discussion examines unpublished documentary material from locations in Caithness, Arran, the Southern Highlands and eastern Lowland Scotland for the application of external renders and lime finishes, the sourcing and supply of materials, and the rationales offered for their continued use by local craftsmen into the nineteenth century.

The contemporary voice of these sources confirms that away from the centres first of Georgian polished masonry and then of the bare-stone fashion of the Ruskin school, harling and limewashing remained the norm for weatherproofing the notoriously water-vulnerable building-stones available to local masons and builders.

For 5 years, I worked as a conservation officer in North Yorkshire. Most Listed Building Consent applications we received for plaster were for 3-coat systems, or occasionally more (SecilTek) could be up to 7); only 2 were for 2-coat work.

Initially, I did not question this, as I had been taught that a 3-coat system was the norm, but on site I noticed that surviving external plasters were either one or 2 coats, and rarely more than 10mm thick in total, quite different to the specifications we received. 

Whilst researching the history of external plasters, I discovered a reference to a ‘thin’ plaster. This term also appeared in 20th century secondary and archaeological sources. No author assigned any significance to the thickness of the plaster, the discussion quickly moved on. However, my interest was piqued.

In 2022, I changed employment and my new role took me all over England. Everywhere, I saw similar thin external plaster on medieval and vernacular buildings, and I started documenting them. This wasn’t a Yorkshire phenomenon; a Lancastrian church, a Shropshire castle – all had similar thin plasters. Furthermore, I recorded similar examples outside England, in Ireland, Greece, Bolivia, for example.

Citing evidence I have recorded on buildings as part of my research and academic references, I will discuss the thin nature of historic external plasters.

I will refer to scientific evidence that the surface area of the coating is more important than its thickness in imparting many of its beneficial properties (promoting moisture transport and evaporation).

The closing discussion points will focus on the following themes:

·       Authenticity

·       Technical performance

·       Economy of labour

·       Economy of materials

§  Financial and carbon implications

·       Barriers to change

·       Question the logic of the established three-coat application.

This presentation asks why we have arrived at the conclusion that ‘harl,’ a thrown external finish should be completed in multiple passes. It is reported in UK repair journals that external finishes should be completed with initial dubbing out, scratch coats, flattening coats and a final finishing coat. This method would be recognised by modern plasterers, but the evidence suggests that a plasterer from the past would not relate to this.

My focus is on the north of England, particularly the Yorkshire area. I have gathered evidence from villages and conservation areas near Ripon, Leeds and Doncaster. I am a sole trader trained in conservation repair. I have found that the evidential historic mortar is very course, thus making it extremely difficult to use a trowel to apply the mortar to the substrate.

Historic buildings in the areas I surveyed are now more commonly externally finished with a flat, modern pointing method rather than a full cover plaster. This could be due to many reasons. Multiple coat plaster systems are expensive. Another explanation could be that full cover renders are out of fashion due to the published works of John Ruskin. It could also be that Listed building consent is required for a full cover plaster, but not necessarily for lime pointing repair work.

The historic buildings in the villages around Leeds have been built using locally quarried soft limestone. I will argue that harling this stone is becoming necessary to prevent irreversible decay and the viability of a one coat thrown harl is comparable to the modern pointing method.

This presentation argues that we have conservation and conservation repair methods wrong, not just in theory but in practice. I will show that this is to the detriment of built heritage.

Buildings archaeology is a discipline which studies the fabric, form and function of a building over time. Its overarching purpose is to understand the way in which buildings were built and how they have subsequently developed, using well-established forms of archaeological enquiry which considers stratigraphic information: vertically and above-ground.

This is different to the more generally destructive nature of commercial, below-ground archaeology. In buildings archaeology, there is opportunity for fabric to be retained and restored in situ, as well as enhanced using archaeological evidence gathering. 

This paper will explore the evolving responsibilities of archaeology in documenting surface finishes on historic buildings – the industry can, and should, champion a new understanding and perspective. To analyse conventional methodologies and their capacity for reinterpretation, we must first look inwards and consider if archaeology itself is deep-rooted in the ideology of bare stone surfaces. The major question posed to the wider industry – are we complicit in the misunderstanding of surface finishes?

Drawing on personal experience and an investigation within accessible archive material, the paper identifies a persistent underrepresentation of surface finishes in current archaeological recording work. This is argued to be attributed to numerous different factors, including inherited method, instilling a lack of engagement and understanding. This has created a knowledge gap leading to limited interpretative expertise, and an undervaluation, ultimately grounding a professional preference for exposed architectural fabric over sustainable finished surfaces.

To address these challenges, the paper calls for enhanced interdisciplinary collaboration, urging closer partnerships between academics, practitioners, and craftspeople to refine methodologies and raise recording standards. There is a call for clearer professional guidance and a more inclusive approach to surface finishes within planning processes and commercial archaeology more widely.

The FabTrads research group at University College Dublin (UCD), funded by the Sustainable Energy Authority of Ireland (SEAI), measured the full hygrothermal properties of two historic lime-based mortars, four plasters, and one render. This represents one of the first studies in which authentic historic materials, rather than fabricated reproductions, have been hygrothermally characterised by experimentally measuring their open porosity, density, sorption isotherms, vapour resistance, capillary absorption and thermal conductivity.

Experimental measurement of these properties is challenging due to the irregular geometry and friable nature of historic materials, requiring adaptations to standard testing methodologies. 

The research presents a compilation of the project’s findings, including:
(1) the hygrothermal properties of historic lime-based materials and how these differ from lime materials currently represented in hygrothermal simulation software;
(2) a comparison of the hygric properties of historic lime-based mortars with newly fabricated hot-lime mixes, assessing their compatibility; and (3) the impact of lime-based renders on the moisture behaviour of traditional solid brick and stone walls based on their experimentally measured hygrothermal properties and hygrothermal simulation using WUFI.

The impact of mortar joints on the moisture storage and transfer in solid brick and stone walls shall also be discussed with an overview of the proposed on-going experimental testing of the follow on TradFabs project.

The loss of traditional external finishes from historic timber-framed buildings may significantly affect both their material performance and architectural legibility. In towns such as St Albans, Hertfordshire, where timber-framing was once the dominant construction tradition, many buildings that previously featured external plaster now show exposed framing.

This reflects a complex history of architectural development, alteration, and survival. While some early timber-framed buildings were designed with exposed, often decorative framing, many later examples were plastered from the outset. These later frames were often built from lower-quality timber, intended to be protected by external finishes, and their exposure has left them particularly vulnerable to accelerated decay.

This paper presents research from a master’s dissertation investigating evidence for removed traditional external plasters to historic timber-framed buildings in St Albans. Three case study buildings, known to have been externally plastered but now showing exposed framing, were selected for detailed analysis. Evidence of lost finishes was identified through close survey of surviving fabric, supported by historic images.

Detailed inspection revealed subtle but legible indicators of removed plaster, including lath fixings, nail patterns, chop marks, and mortar staining. These observations were systematically recorded and used to develop a practical checklist for identifying and interpreting lost traditional plaster finishes.

The findings show that even fragmentary evidence can be read through careful observation, and often reveals additional aspects such as previously unknown alterations and development. Recognising these traces provides a strong evidence base for more sustainable approaches to conserving historic timber-framed buildings, guiding decisions about maintenance, repair, and potential reinstatement.

In the context of climate change – characterised by increased rainfall, humidity, and extreme weather – maintaining or reinstating appropriate external finishes can protect vulnerable timber, enhance building resilience, restore authenticity of form, and shift conservation practice toward interventions that are evidence-based, environmentally responsible, and long-lasting.

The English Lake District, England’s largest National Park and a UNESCO World Heritage Site, is internationally valued for its cultural landscape and distinctive vernacular buildings. While whitewashed cottages are widely celebrated as emblematic of this heritage, exposed bare stone is the more dominant feature, promoted as authentic for historic buildings and most new development.

This prevailing narrative persists despite extensive physical, documentary, and performance-based evidence demonstrating that lime finishes were historically widespread and remain critical to the long-term sustainability of traditional masonry in a wet and increasingly volatile climate.

This paper explores to what extent the evidence can be deployed to challenge the entrenched preference for bare stone and to reframe lime finishes as a necessary, evidence-led response to climate breakdown, building performance failure, and heritage conservation. Drawing on archival sources, and real-life case studies, it demonstrates that the bare stone aesthetic represents a shifted baseline and a well-meaning reaction against cementitious renders, rather than historic authenticity and data-based decision making.

The paper argues that the absence of lime finishes within living memory should not be used to justify poor building performance or the continued erosion of traditional vernacular construction knowledge.

Managing change within a National Park and World Heritage Site presents challenges, including limited regulatory leverage, permitted development rights, constrained funding, and gaps in professional and craft expertise. These barriers are compounded by emerging policy pressures, including proposed amendments to the National Planning Policy Framework that may tolerate increased harm to heritage assets in pursuit of energy efficiency.

The paper contends that reinstating lime finishes offers a low-impact, highly effective means of improving thermal and moisture performance while safeguarding heritage significance. Ultimately, this talk argues that shifting practice requires not only technical evidence, but a conscious effort to reset cultural expectations of authenticity, sustainability, and care for traditional buildings.

This paper examines the role of external surface finishes, particularly limewash, in the interpretation of medieval castles that are now partially or largely lost. Drawing on multidisciplinary practice exemplified at Dover Castle, it explores how visualisation can integrate historical, architectural, and archaeological evidence where little or no fabric survives.

Chester Castle in Cheshire offers a 13th–14th-century test case, where documentary references to lime and regional material supply raise questions of symbolism, authority, and selective surface treatment within a wider political landscape.

At Chester, lime sourced from newly conquered north-east Wales suggests that exterior finishes were not merely functional, but materially Welsh, symbolically English, and politically charged. Where castles are largely invisible today, interpretative drawings and digital imagery often provide the only means of addressing such finishes, allowing historically attested limewashing to be shown rather than omitted by default.

The paper argues that external surfaces should be treated as historical actors, and that uncertainty – clearly signalled – can strengthen interpretation rather than weaken it.

Positioned within ongoing research, this contribution reflects the perspective of an historian and archaeologist engaged with heritage interpretation and landscape study. It proposes a context-led, transferable framework for presenting external finishes at lost and fragmentary castles across the UK and Ireland, opening discussion on how absence, visibility, and ethics shape contemporary heritage presentation.

This talk is based on work commissioned by Historic England as part of their Damp Church Towers project. Conservation practice shows that lime rendering can remedy chronic damp in a medieval church tower. This is an expensive, technically complicated solution and the alteration it brings to the appearance of a church is always a thorny problem.

The conviction that medieval tower stonework was always exposed is widespread. If the irrefutable fact of damp cannot overturn conviction, can documentary evidence change perceptions? 

Documentation found is heavily-skewed towards the 19th-century resource, over four centuries after most of Devon’s church towers were first built, but it can prove that 25% of medieval church towers in Devon were once lime-finished, although not when.

There are now 64 rendered church towers in the county, including those that are cement-rendered. 13 of the 64 have been re-rendered with lime since the late 1980s. 

The documentation raises questions of how little we know about the external appearance of medieval churches and other medieval stone buildings through time. Were all medieval church towers lime-finished? Was this for weather-proofing and/or aesthetics?

The Victorian conviction that the Georgians had buried church architecture, including its archaeology and structural faults, in ‘an avalanche of lime’ prompted the process of stripping and scraping that was ongoing in the early years of the 20th century and has left us with an external image of the medieval church that is not very medieval at all.

This presentation investigates the declining use of traditional external lime surface finishes on historic church buildings in Perthshire, Stirlingshire, and Angus, and examines the implications for fabric performance in an era of accelerating climate change.

Recent and ongoing studies have shown that Scottish churches were frequently constructed with rubble masonry and thick permeable walls that relied on a variety of lime finishes to mitigate wind-driven rain, moderate moisture movement, and reduce long-term decay. Despite this, a growing number of churches are now left partially or wholly without protection, often following capital repair programmes.

Using a mixed-methods approach combining field survey analysis, case-study review, archival conservation records, and stakeholder interviews, the research identifies a systemic pattern in which surface finishes are treated as optional or aesthetic rather than as integral elements of building performance.

Case studies from the geographic areas mentioned, reveal extensive masonry repairs completed without reinstating protective finishes, leading to accelerated mortar and sandstone erosion with accompanying moisture ingress. In Stirlingshire, impermeable cementitious renders applied to church halls resulting in interstitial damp and internal fabric deterioration within two to three years. Perthshire examples demonstrate how stripped façades, often justified through notions of material “honesty,” perform poorly under increased rainfall and freeze–thaw conditions.

The study identifies three principal barriers: grant funding structures that prioritise structural stabilisation, or a preferred, mechanical and electrical installation over climatic protection; local authority and ecclesiastical regulatory frameworks that inadequately integrate hygrothermal performance into decision-making; and a decline in specialist knowledge and skills relating to lime-based finishes within the church repair sector.

The findings argue that the omission of appropriate surface finishes undermines both conservation outcomes and climate-adaptation objectives. Reframing lime harling and render as essential climate infrastructure is critical to ensuring the long-term resilience, sustainability, and community use of Scotland’s historic church buildings.

Recent and ongoing research in Scotland has described a very different architectural landscape to that which is commonly understood within the heritage community and the wider public.

The study demonstrated a pattern of completely covering masonry with a variety of lime finishes, predominantly harl, from the early medieval period through to the twentieth century. Through time those finishes evolved into partial cover and then complete exposure of the stone - and with this evolved Scotland’s 16 known pointing styles.

In this paper I explore lime finishes in North Yorkshire, using more robust methodologies than in previous studies and employing citizen science to reveal an (as yet) unrecognised and rich tradition of wall coatings. I illustrate how masonry was conceived as an integrated whole – built and plastered inside and out as a single operation.

In towns and villages such as Masham, Middleham and Redmire, almost the entirety of the buildings retain evidence of finishes. I illustrate what form this took and how the visual landscape once read much differently than today. Evidence suggests that at medieval ecclesiastical sites, such as Fountains Abbey, the underlying masonry - what has previously been regarded as ‘ashlar’ - was simply a convenient means of producing flat walls and to create a surface onto which a polychromatic scheme was applied, inside and out.

Significantly, that decorative order was painted ‘ashlar’, or fictive masonry, allowing them to create the illusion of perfection, rather than presenting the disorder of poorly bonded and coursed masonry.

The study has wider implications for how we understand other ecclesiastical buildings, where polychromatic work remains internally and asks us to consider whether the external fresco work found in parts of Europe, where Catholicism remains the dominant form of worship, was also part of the language of religious building in pre-Reformation England.

External finishes on historic masonry – such as those promoted by the SPAB – have often been undervalued, misunderstood or removed in the pursuit of bare stone. This talk examines the SPAB’s approach to traditional finishes and explains why it is increasingly relevant for the care of historic buildings in a changing climate.

The SPAB is sometimes thought to insist on a strict ‘preserve as found’ approach that discourages reinstating lost finishes. Tracing its origins as the 19th-century ‘Anti-Scrape Society’ the presentation shows that the SPAB has long supported both the retention of historic renders and, where appropriate, their careful reinstatement. Its guidance balances technical considerations such as moisture management, wall protection and material performance with respect for a building’s history and the interests of those who value it, including local communities and occupants.

Case studies from past and recent projects demonstrate that surface finishes are far more than decorative. Traditional renders protect masonry, moderate environmental exposure and manage moisture. In an era of heavier rainfall, extreme weather and accelerating material decay, reinstating or maintaining these finishes provides a practical, low-carbon and resilient way to keep walls drier and warmer.

They can also reinforce architectural composition, for example by visually uniting windows, doors and other detailing that may appear isolated on bare walls.

Decisions about intervention must consider context. Reinstatement is appropriate where historic renders have been lost, exposure is causing rapid deterioration or original detailing risks appearing isolated. By contrast, caution is needed where bare walls are original, valued for their worn character or help tell a building’s story.

By reconnecting long-established principles with contemporary performance needs, this talk argues that moving beyond bare stone is essential to the sustainable care, resilience and legibility of historic masonry for the future.

There has been large-scale loss of external surface finishes from historical buildings. The extent of this loss has arguably dropped out of public awareness; the present appearance of buildings is normalised. The visual memory of surface finishes has endured in some places but not in others.

Utilising the Historic England Archive (Red Boxes), focusing on the county of Cumbria (284 civil parishes), this paper scopes out the potential for such archival resources to contribute towards presenting an unambiguous, visual case to a public audience for the historical use of such finishes throughout Cumbria.

Underpinning the survey is a database with records for more than 467 sites, covering buildings listed at all Grades as well as many unlisted vernacular buildings. Having extracted relevant archival images, the buildings in the images were identified, located and researched. Modern images of the same buildings were obtained indicating what had happened to the surface finish to the present day.

Clear patterns have emerged from this survey, shedding light on when finishes are likely to be lost or retained. Loss includes deliberate removal as well as gradual erosion. Certain trends relate to certain types of buildings more than others.

Differences between parish churches compared to other non-conformist religious buildings have been identified. Other changes relate to the conversion of ancillary buildings into buildings with a residential function. Modern conservation techniques and materials do not necessarily always replicate past, historical appearance.

Bearing in mind caveats that will be clearly outlined in the paper, the results of the survey are another vital strand of evidence to inform best practice for the care and conservation of our historical buildings. Next steps for potential future research elsewhere will be touched on briefly.

In 2023, works were undertaken to Scarborough Rotunda Museum, repairing the external masonry. The harsh maritime environment had caused severe erosion to the calcareous sandstone.

The repair strategy was a two-part process, restoring the crisp neoclassical profile of the building with mortar repairs to spalling surfaces, and applying a lime-based sheltercoat, composed of natural earth pigments, NHL lime binder, stone dust and sand, to protect the weathered stone and avoid the need for more extensive masonry interventions.

This was a considerable change to the building, the finish of which was always exposed stone. The ruined appearance was detracting from the neoclassical façade, but to reinstate this in a like-for-like manner would have involved expensive and invasive stone replacement.

Our methodology offered an innovative, cost-effective solution to the aesthetic and technical repair needs of the Rotunda. 

Our specification was designed in collaboration with the conservator, and employed on-site trials. The mortar was a proprietary NHL based stone repair mix supplied pre-pigmented while the sheltercoat was an on-site designed mix darkened with earth pigments to match the adjacent stonework and using an NHL lime binder to provide higher resistance to erosion in the exposed marine context.