Many thanks to Michael Plageman, who has provided the below. Michael is a Chartered Architect, Registered Conservation Architect, at Davies Sutton Architects and is a Design Review Panel member, attending Design Review Panels across the South West; in Cornwall, Devon (both Plymouth and Exeter), Dorset, Wiltshire and Swindon.
"To anyone who has looked closely at historic stone buildings and monuments, the deterioration of stone is an ongoing and evolving characteristic. As part of an un-carved, mass rubble stone wall, such deterioration can be aesthetically attractive and has been referred to on occasion as ‘pleasing decay’, however, the effect on more refined stonework, such as buildings designed in a classical style for instance, can be more detrimental. Indeed, at its extreme, it does not take much for the deterioration of a carved piece of stone to lead to a sculptor’s original intention being lost altogether. Therefore, with a large proportion of Britain’s cultural heritage constructed in stone, there is an ongoing battle to prevent the significance of these monuments being compromised and lost to future generations.
Cardiff based practice, Davies Sutton Architects, embraced the philosophical and technical challenges presented of managing such decay mechanisms, in their undertaking of stone repairs to the South façade of Apsley House – a Grade 1 listed building of considerable national importance and significance in central London. The practice specialises in the conservation of historic buildings, together with new buildings on sensitive sites and their portfolio of works includes interventions to an array of outstanding buildings and sites such as Chiswick House, Cleeve Abbey, Tintagel Castle and St Woolos Cathedral. Working on such buildings demands a particular level of care, dedication and research to be carried out before implementing conservation repairs. Consequently their experience of such working methods and requirements positioned them appropriately to accept English Heritage’s appointment to undertake the works.
General view of the South elevation of Apsley House from the South West, circa 1853
Located on the junction of Hyde Park corner and Mayfair, Apsley House once ‘stood at a focal point of the topography of London and, equally, its social and political fabric.’ It was the first house to be seen after the tollgates to the City of London, and as such, has subsequently been commonly referred to as No.1 London. Originally designed by Robert Adam between 1771 and 1778, as a brick building for Lord Apsley, the house was passed to the Duke of Wellington’s family in 1807, and the 1st Duke soon commissioned Benjamin Wyatt to reorder and reorganise the house in the latest fashion to reflect his rising status.
The property now comprises of some of the country’s finest interiors, including retained decorations by Robert Adam and the Waterloo Gallery by Wyatt – an extravagant Regency interior which marks the Duke of Wellington's famous victory over Napoleon. In addition to this, Wyatt also remodelled and reclad the property in Bath stone, thereby projecting the Duke’s growing sense of grandeur, elegance and order into the public realm where it has been the backdrop for London life ever since.
The re-routing and widening of roads in the 20th century, together with surrounding development, means that the house is now predominantly isolated and disconnected from its historic context. There has also been a marked change in the natural environment that contextualises the house, with the thunderous and heavily trafficked roads of Piccadilly and Park Lane to the South and East, replacing the less polluted and sedate environment that the building used to enjoy.
Commissioned by English Heritage, Davies Sutton undertook an initial feasibility study and assessment of the South elevation of the house as part of an ongoing , phased repair programme that had previously addressed the North and West elevations. The study identified that the South elevation had suffered environmental damage, strongly associated with its urban location, that was detracting from the significance of the building. A cursory inspection was also made of the remaining elevations of the building to both contextualise these findings and to ensure an overview of the condition of the building as a whole was understood.
Visual inspection of the South facade established that there was a general blackness to the stonework. This was caused by sulphuric acid and calcium carbonate in the surrounding environment ,dissolving in rainwater, mists, fog and general condensation, and being absorbed into the stonework. The acidic water was reacting with the lime in the Bath stone to form calcium sulphate, and as the water evaporated from the surface of the stone, the resulting calcium sulphate crystallisation was fixing dirt onto the surface of the stone, forming the black pollution crust.
Comparison of the West (left) and South (right) elevations of Apsley House, shows the appeal of rich, warm colour of the copperas decoration to the Bath stone retained in sheltered areas of the South elevation. Note also the context of the house.
The sulphate crystallisation was subsequently not being washed away – particularly in sheltered spaces such as the underside of the cornice, the dentil course, architrave and the stringcourse – leading to concentrated deposits of pollution crusts to sheltered areas of the façade. In addition to this, a number of poorly executed repairs had been carried out which were both a bad visual match with the surrounding stone, and that were also causing further damage to the stonework. There were two types of repair that had been undertaken – cement based repairs and lime-based repairs. With regards to the cement based repairs, the dense impervious nature of the material, whilst visually being an unsuitable match for the Bath stone, was leading to moisture and salt concentrations around them, and concentrating areas of decay. This was leading to small sections of masonry falling from a high level to the public forecourt below - an obvious health and safety issue.
With regards to the lime based repairs to the building, whilst it was unlikely that these repairs were damaging the surrounding stonework, the mortar used for the repair was unfortunately a poor match. The colour was too dark and the exposed aggregate gave a contrasting texture with the original stone. Such repairs were therefore affecting the presentation of the building and this was on a reasonably significant scale.
The feasibility study allowed the practice to understand the type of decay mechanisms at work, and to guide further investigations. It also enabled initial ideas to begin to be developed for interventions to repair and manage subsequent decay. These proposals were set against a desire to preserve, conserve and enhance the presentation of the building which was embodied in the wider Conservation Management Plan for the property. The general and overarching principle was consequently to retain as much of the original fabric as possible whilst undoing previous repairs where they were causing damage or were inappropriate to the presentation of the building. Underpinning this approach was the premise that the decay of historic fabric, particularly stonework, can affect the architectural impact of a building, as well as encourage and accelerate further deterioration. Therefore, the early repair and maintenance of the historic fabric in situ, in advance of significant deterioration, would play a substantial and important role in guiding conservation decisions going forwards.
Detailed Assessment and Repair Proposals
Following the initial feasibility study, the practice undertook a detailed survey of the South façade of the House together with commissioning a structural overview of the elevation. This was aimed at mapping out the condition of the facade on a stone by stone basis so that quantifiable repair proposals could be developed. The survey also provided an opportunity to undertake and investigate trial repairs and interventions on discrete areas of the building to inform suitable repair techniques going forwards.
It was proposed that previous cement-based repairs would be cut out and replaced with Bath stone to exactly match the type and profile of the existing stone to the building. Through discussion with stone specialists, together with visual matching, this was identified as being a Bath stone being quarried at Hartham Park. Its selection for repairs meant its properties would be commensurate with the existing stone of the facade and therefore give the best chance of minimising any adverse reactions with the existing stone, together with being a much better visual match.
With regards to the lime based repairs to the building, whilst these were effectively sacrificial elements to the facade, they significantly affected the presentation of the building as they deteriorated. It was therefore proposed that these repairs would also be cut out with new stone pieced to provide a repair with more longevity that better matched the existing stonework.
Cement render & delaminating
stonework to the parapet, presented a danger as it could fall to the forecourt below