CONSERVATION OF MAR LODGE BRIDGE,

for National Trust for Scotland

MARCH 2021

Heritage Impact Assessment 2 Conservation of Mar Lodge Bridge, Braemar for National Trust for Scotland: Heritage Impact Assessment

1.0 Introduction

The purpose of this report is to provide a Conservation Statement and Heritage Impact Assessment in relation to a Listed Building Consent/Planning Application by the National Trust for Scotland (NTS) to repair the Mar Lodge Bridge, Braemar.

The Planning Application team is engineer-led, by Allen Gordon Ltd, and the application submission is steered by Local Planning Authority guidance within Pre-Application advice note ENQ/2020/1789.

This particular report should be read in conjunction with separate reports by Allen Gordon Ltd ‘Engineering Conservation’ (March 2021) and by Historic Metalwork Conservation Company Ltd ‘Victoria Bridge’ (Sept 2019).

2.0 Background

The Mar Lodge Bridge provides the main route into the over the Rive Dee, just west and upstream of the historic village of Braemar in the heart of the Cairngorms National Park. There are remains of a 19th century designed landscape on the north side of river, with fragments of depopulated vernacular settlements to the east, i.e. at Allt A’Chlair, and the west at .

Mar Lodge itself was built in 1895-98 by north-east architect A Marshall MacKenzie for the Duke and Duchess of Fife as their autumn residence on the site of an earlier house (c.1780), which had been damaged in the Muckle Spate of 1829. This earlier house had in fact been rebuilt in the 1830s, but was destroyed by fire in 1895. Originally known as 'Dalmore House’, it is thought that a lodge may have occupied this site as far back as the 16th century. Dalmore House was bought by entrepreneur William Duff in the 1730s and, in the years that followed, minor lairdships were gradually absorbed as the estate expanded.

In the 19th century, the estate was used primarily for recreational shooting and fishing. In 1879, Alexander Duff succeeded his father James, becoming the 6th Earl Fife. In 1889, he married the Princess Royal and was made 1st . Following his death in 1912, the estate was managed by trustees, later passing to Princess Alexandra, Duchess of Fife. 3 Conservation of Mar Lodge Bridge, Braemar for National Trust for Scotland: Heritage Impact Assessment

In 1959, the estate was inherited by Alexander Ramsay, who then sold it to the Ashdale Property Company in 1962. They almost immediately passed it onto the Swiss Panchaud family. They ran it as a sporting venture, with the Lodge set up as a hotel. In 1989, it was bought by Mar Lodge Estate Inc. who continued to run it as a sporting venture; but giving greater emphasis to sensitive land management.

In 1995, the estate was acquired by the National Trust for Scotland, with additional funding coming from both public and private organisations that also allowed an endowment to be created. Scottish Natural Heritage then became a partner in the management of the estate, whilst NTS converted the former hunting lodge into holiday flats. A desk-based survey of the estate was carried out in 1998, and a standing building survey of five croft houses was carried out in 2000.

Severe flooding of the River Dee in 2016 (the subject of national news at the time) badly scoured the site of the bridge, which also threatened to undermine its piers leading to collapse. The NTS, therefore, commissioned a specialist investigation into the condition of the bridge. This Planning Application for proposed repairs and conservation is the outcome of that investigation.

The proposals are the NTS’s first action to repair the bridge since its takeover in 1995; the interventions are deemed important and much-needed.

Extract from the 1st OS map, surveyed in 1866, showing the ‘Victoria Bridge (Wooden)’ and south Gate Lodge in position. Note that this earlier bridge had its north abutment slightly more east of the present bridge. The bridge and lodge are shown in very similar detail within the 2nd OS map, surveyed 1901 4 Conservation of Mar Lodge Bridge, Braemar for National Trust for Scotland: Heritage Impact Assessment

3.0 Significance of the bridge

3.1 Historical association

Mar Lodge Bridge (sometimes referred to locally as ‘the White Bridge’) was built in 1905 as the main approach to the Mar Lodge complex for Alexander Duff 1st Duke of Fife and his wife, HRH Princess Louise. The royal association of the Estate is honoured with important inscriptions on the bridge to ‘Queen Victoria 1848’ and ‘Edward VII 1905’.

The current Edwardian ‘white bridge’ replaced an earlier timber one of 1848 and, noting the occupation of the Estate from the 18th century, there was most likely a previous timber bridge before the Great Flood of 1829.

3.2 Construction

Historic Environment Scotland acknowledges that as well as being used for communication, bridges can be major architectural features in a town or landscape. The materials used are also of interest and can be important to the history of engineering. High importance is attached to historic fabric when it conveys information about how it was created and how it performed.

The bridge is a delicate but striking manmade feature in a spectacular landscape. The long span bridge has iron lattice girders supported on 4 sturdy stone piers with convex masonry approach walls. The piers are constructed with rounded ends using bull-faced pink and grey granite and flushed pointed mortar. The lattice frames are formed of rolled steel sections riveted together, including angles, flats, ‘T’s and channel sections, with a criss-cross arrangement of steel channel and flat sections. Sitting inside of the main bridge girders are a series of repeating decorative cast iron panels forming a secondary protective railing.

The bridge deck is made from a series of curved/arched steel deck plates riveted between steel ‘T’ sections that sit on the lower edges of the steel girders. Interestingly, and importantly as on-site ‘archive’ information, a number of steel items have the makers’ names rolled on their metal surfaces. Lying on top of the steel deck plates is a layer of lightweight concrete topped with a road paving material.

Much of the bridge’s distinctive appearance is derived from its skilfully designed and constructed iron latticework, which is augmented by an ornamental cast iron handrail and a horseshoe arch that, together with a small symmetrical stone gatehouse opposite, elegantly frames the entrance. 5 Conservation of Mar Lodge Bridge, Braemar for National Trust for Scotland: Heritage Impact Assessment

[See separate reports by Allen Gordon Ltd ‘Engineering Conservation’ (March 2021) and by Historic Metalwork Conservation Company Ltd ‘Victoria Bridge’ (Sept 2019) for further construction details].

3.3 Setting

The Estate is now a National Nature Reserve sitting within “The largest and most the Cairngorms National Park and containing several important nature nature designations (SSSI; SAC; SPA). The area is reserve in Britain” popular with tourists from all

over the world and many walkers exploit the Estate’s Hidden Scotland public access and right to roam. Tourist vehicles, however, are not permitted over the bridge and there is a weight restriction for other vehicles that service the Estate.

Mar Lodge Bridge is a Category B Listed Building (1985) : one of five Listed Buildings on the Estate. The bridge is a significant landscape feature in its own right, and the hunting lodge is set within a designed landscape.

At the public road end, there is a gate and a gatehouse that was occupied by a gatekeeper when Mar Lodge Estate was owned by the Duffs. It is a one-storey, coursed granite tetrastyle with a piended, slated roof. The north facing building has an elaborate, colonnaded portico with four pink

granite pillars at the front, and four matching pilasters “Mar Lodge Estate is within the masonry of the north wall. a walker’s paradise” An old Scot pine tree stands on the south side of the road, Visit Scotland to the west of the bridge. Tradition has it that this was the gallows tree for the barony.

Extract from the 1969 OS map showing the bridge (still referred to as ‘Victoria Bridge’) in its current position 6 Conservation of Mar Lodge Bridge, Braemar for National Trust for Scotland: Heritage Impact Assessment

Black and white photo of the bridge taken in 1970 showing the structure in good condition, with no obvious signs of corrosion, damage to stonework and/or erosion of embankments. Note, however, the concrete protection around the base of the piers.

Today, the white iron bridge is a striking manmade feature within a natural setting 7 Conservation of Mar Lodge Bridge, Braemar for National Trust for Scotland: Heritage Impact Assessment

4.0 Current Condition

The bridge has clearly been maintained down the years – there is evidence of repair work to the ironwork and stonework – so the bridge is largely intact and still true to its original design. However, the bridge has suffered considerably on account of the last major spate (2016) as well as ongoing movement/vibration caused by nature and vehicles.

Although not showing concerning signs of movement, the footings of the bull-faced granite piers have signs of ongoing scouring, and there have been previous concrete-based interventions to inhibit fluvian impact. Attempts to minimise scouring in the past using shuttered concrete and concrete bags are now visible at the footings. The embankment on the north side of the bridge has been badly eroded as the river has, more recently, changed course. The north pier is now being sacrificed to the river and the stone base of the pier is being exposed. Two piers have been designed to sit within the river but, due to scouring of the riverbank, an abutment is now at the water’s edge. The south side of the embankment is less scoured, but the south-west curved stone wing wall at the bridge entrance has visible signs of structural movement and currently has temporary supports (see Allen Gordon report). The wing walls supporting each embankment are built using a mix of finely jointed grey and pink fair-faced granite. The pointing, which has been repaired in various places down the years, is generally now a cement-based raised tuck point using building sand with a flat edge c.10-15mm. An attempt to stabilise the abutments of the north and south walls is obvious, with several stainless steel straps cut into the stonework at various intervals. This work includes some resin based mortar to the jointing. On the south side, there are obvious, but less severe, interventions in the form of vertical timber supports bolted into the south west embankment wall.

The surface of the iron and steel bridge is now tarred, with areas pitted, and parts of the surface are no longer draining properly. As a result, vegetation has built up around the steel and cast iron leading to corrosion, with some vegetation growing at the edge of the road deck causing blockage of several (pvc) drain outlets.

The bridge ironwork has previously been cleaned, repaired and repainted, and there are unfortunately no indications of historic paint layers (possibly sand-blasted clear in the late 20th century). However, these paint coatings have begun to fail, and corrosion is most severe at the bottom of the steel channel compression members where they met the bottom chords. The connecting steel sections have a layer of rust present along their bottom faces.

The bridge was originally made up of three independent sections in order to accommodate movement, but large steel plates have been bolted across the top joints to the three girder spans, presumably in order to stiffen the structure to counter vehicular vibration. However, this intervention may have altered the ‘flexible’ dynamic relationship between the ironwork and stonework. This is particularly noticeable at and around the masonry at the south end entrance, whereby the parapets to the convex wing walls have severe cracks through the stones themselves and are tipping towards the road. It is also very noticeable at the two abutment wall plinths that support the horseshoe archway, where there are obvious signs of displacement in the upper courses of stone blocks, with sections of the gate piers having rotated out of position.

Extract from the 1969 OS map showing the bridge (still referred to as ‘Victoria Bridge’) in its current position 8 Conservation of Mar Lodge Bridge, Braemar for National Trust for Scotland: Heritage Impact Assessment

View from the north west embankment Close-up view of the entrance wing wall showing the scouring to the north pier base, showing movement cracks in the masonry. corrosion of the ironwork, and temporary supports to the south west wing wall

Close-up view off the iron structure showing Close-up view of the later plate fixing debris and vegetation on the deck and across the top of two of the main iron significant corrosion to the main beam and balustrade sections. cross girders.

Extract from the 1969 OS map showing the bridge (still referred to as ‘Victoria Bridge’) in its current position 9 Conservation of Mar Lodge Bridge, Braemar for National Trust for Scotland: Heritage Impact Assessment

5.0 Approach to conservation

The approach from the outset has been to conserve the bridge based upon a thorough understanding of the structure’s history, design, and construction, use of materials, performance, and risk. In this respect, the approach conforms to Managing Change in the Historic Environment ‘Engineering Structures’ Guidance 2010. Further technical advice and knowledge has been gained from HES various publications : ‘Managing Change in the Historic Environment: Use and adaptation of Listed Buildings’; ‘Managing Change in the Historic Environment: External walls’; ‘Managing Change in the Historic Environment: Works on Scheduled Monuments’; ‘Scotland’s Listed Buildings guide for owners and occupiers’; ‘TAN Preparation of Lime Mortars’; and ‘TAN Stone masonry skills and conservation’ ; ‘HES INFORM : Ironwork’; and HES ‘Advisory Standards of conservation and repair for the historic building environment in Scotland’. The character and historic fabric of an engineering structure is best maintained by repairing components on a like-for- like basis. Any damaged, decayed or missing item should be repaired or replaced in its original form and material.

5.1 Priority

The priority is ‘to conserve the bridge from collapse and extend its life serving its original purpose as main approach to the estate’.

5.2 Key Objective(s)

The key objective to retain as much historic fabric – stone, ironwork, timber, paint colour - as possible, with minimal loss of original fabric alongside repair and replication of original materials and detailing.

Where historic fabric is missing or defective, it will be replaced using matching materials to restore and prolong structural stability.

Contemporary interventions will, so far as possible, be wholly reversible.

The success, or otherwise, of the interventions will be monitored and reviewed over time. 10 Conservation of Mar Lodge Bridge, Braemar for National Trust for Scotland: Heritage Impact Assessment

6.0 Proposed interventions

The scope of proposed works generally involves repairs to stonework, ironwork and the deck surface, which includes rainwater disposal.

6.1 Masonry work

The base of the north pier will be protected sufficiently to safeguard the structure for the foreseeable future, but done in such a manner as to preserve and conserve the historic stonework itself. Without damaging historic stonework, the existing defective concrete will be carefully removed. A rock mattress will then be located around the pier to provide a stable base and the pier masonry will be shielded from erosion by a sacrificial twin layer of smooth precast concrete, pigmented to match the colour of the pier stonework.

The south east entrance parapet wall has distorted and settled into place, thus threatening long- term stability and public safety, so requires taking down and rebuilding. The stones will be numbered during dismantling and any broken stones should be repaired for reuse and/or replaced to match. Stone strength, colour, tooling, coursing and jointing should be carefully matched in any new work and pointing and grouting should be undertaken with the greatest care. The stones of the gate piers will be dowelled and bonded in order to prevent future distortion.

Noting that the current structure was built in 1905, it may well have been built using a cement- based mortar, which would not permit much movement in the masonry sections. Since it is unclear to the eye what the original mortar is, mortar analysis is proposed at different sections of the structure. Consideration to rebuilding in a medium strength lime mortar with movement joints at each end will be given, in order to allow greater movement and flexibility across the structure.

6.2 Ironwork

The bridge’s entrance gates, archway and decorative ironwork will be labelled, recorded and removed from site to workshop conditions for specialist conservation treatment prior to reinstatement. Conservation work will include the careful gas-welded reinstatement of missing cast iron features.

The structural ironwork will be blast cleaned before being treated and re-painted white. Blast pressures will be controlled to ensure that lettering, decorative features and fragile sections are not irrevocably damaged. 11 Conservation of Mar Lodge Bridge, Braemar for National Trust for Scotland: Heritage Impact Assessment

Heavily corroded steel channel compression members will be repaired in-situ with ‘spliced’ plates retaining as much original fabric as possible, whilst small wasted areas will be consolidated with a polyester sanding filler before priming and painting. (Refer to Historic Metalwork Conservation Company Ltd report).

The later steel plates that connect the three span sections will be removed and reinstated with a flexible joint that permits longitudinal movement caused by thermal fluctuations and/or mechanical vibration. A similar flexible joint will be included into the gate archway, in order to allow it to flex without stress loading the gate piers.

6.3 Deck surface and iron structure

It is proposed to remove the deck surface and concrete infills to the edges of the roadway and expose the lower lattice beam for further inspection. The structural girders will be blast cleaned and any wasted areas will be repaired to match before paint treatment. (Refer to Historic Metalwork Conservation Company Ltd report).

The deck surface will be replaced with an improved drainage detail and replacement metal outlets to ensure water is properly cleared from the cast iron elements to prevent future deterioration.

The deck will be surfaced using high quality mastic asphalt with a non-skid finish laid to fall.

7.0 Heritage impact assessment

7.1 Risks to built heritage

The main risks to heritage within this project application relate to lack of intervention, i.e.

a) Collapse from spate or erosion, leading to major heritage loss; b) Closure on safety grounds, e.g. deck, ironwork, piers, leading to loss of original purpose.

Lesser, but still important, risks to heritage relate to the interventions themselves, i.e. c) Damage to ironwork during blast cleaning (although noted that current paint and decking finishes are not historic); d) Loss of historic information, e.g. ironwork lettering, masons’ marks etc; e) Inappropriate material choices, e.g. metalwork, mortar, stone, paint, colour choice.

A significant risk to heritage, albeit it is outwith the deliberate scope of this project, would be the loss of the submerged remnants of the former timber bridge. 12 Conservation of Mar Lodge Bridge, Braemar for National Trust for Scotland: Heritage Impact Assessment

7.2 Mitigation Steps

Addressing the main risks to built heritage is the core purpose of this project, which seeks to :

(a) Protect the bridge piers and embankments from further erosion; (b) Stabilise the masonry abutments and wing walls; (c) Stabilise and repair bridge ironwork; (d) Repair decking and rainwater disposal system.

Addressing the risk potential of the interventions will focus upon :

(1) Using matching materials, or close replicas where no longer available, to exact ingredients, design and/or colour as existing; (2) Careful dismantling and accurate reconstruction of any items requiring structural stabilisation; (3) Decorative ironwork and royal name plaques being taken off –site by specialist contractor; and only using hand tools when working on fragile sections; (4) Reviewing interventions once work gets underway and structure further exposed; (5) Recording details for handover to client for future maintenance work; (6) Regular inspection and monitoring the success (or failure) of the interventions.

The client will be encouraged to carry out regular inspection and maintenance, including commitment to a regular schedule of painting to prevent corrosion.

Note : protection of the submerged timber bridge remnants should be given high priority (through consultation with an archaeologist, if required), since survival of these structures in their original form is rare. On the basis that it is ring-fenced to be outwith the scope of the project (cross ref with Contractor Method Statement), there are no current proposals to record the timber remains. 13 Conservation of Mar Lodge Bridge, Braemar for National Trust for Scotland: Heritage Impact Assessment

Mar Lodge, Braemar Heritage impact assessment matrix

Risk Impact Intervention Significance Mitigation Traffic light Comment potential potential Ensure pier footings are Exercise requires avoiding protected below water work anywhere near timber level in concrete coloured Amber remnants of former bridge Protection of High to match riverbed gravel below water line 4 5 warning pier footings (20) and capable of downstream. reversibility without (12) Protection of piers affected permanent damage to by natural forces outwith stonework control. Requires full photographic Reconstruct survey, measuring and stone stone Ensure reconstruction in Green numbering; ss plates and abutment High same materials and to pinnings to be concealed and resetting 4 4 (8) (16) exact design as existing from view; mortar mix to of masonry match existing in colour and parapet piers texture Ensure retention and Repair of conservation of existing Requires work to be carried ironwork, ironwork structural Amber out by specialist contractor. (incl re- Medium members and decorative Features with decoration providing 5 3 warning (15) work, with minimum and/or text to be particularly element of (10) replacement to match in safeguarded and conserved. flexibility) detail Requires inspection during Ensure repainting in high Repainting of Medium Green paint stripping process to quality metal paint in ironwork 4 3 ensure no original paint (12) same colour (5) samples remain Ensure removal of existing tarred surface Requires photographic Repair of Low Green without damage to survey and recording of all deck surface 2 3 (6) structural or decorative (4) details to be repaired/altered ironwork

Scoring: 17-25 High impact; 9-17 Medium; 0-8 Low 14 Conservation of Mar Lodge Bridge, Braemar for National Trust for Scotland: Heritage Impact Assessment

8.0 Conclusion

Mar Lodge Bridge is an important historic and architectural structure that is currently at risk from erosion and corrosion and, therefore, in need of intervention. The bridge is now owned by a responsible custodian (National Trust for Scotland) who has commissioned a specialist engineer- led design team. The need for intervention has been carefully considered with a conservation approach from outset, and the impact upon built heritage has informed the design process throughout.

As a result, mitigations have been put in place and will be monitored during and after the works.

The processes and materials proposed should not result in any adverse effect on the structure and will conserve and maintain the structural and visual integrity of engineering structures and their associated features. The proposals should impact positively upon its built character and wider landscape contribution to the cultural heritage of the Cairngorms National Park.

Report by Dr Nick Brown BSc(Hons), Dip Arch, Pg Dip, PhD, RIAS, RIBA, RTPI, IHBC, FSAScot, MInstLM RIAS Accredited in Conservation and in Sustainable Design NB/PB March 2021 APPENDIX

Listed Building Statutory Info (LB3002)

Category B Date Added 18/03/1985 Local Authority Aberdeenshire Planning Authority Aberdeenshire Parish Crathie and Braemar National Park Cairngorms NGR NO 10223 89564 Coordinates 310223, 789564

Description

1905. 3 span decorative lattice girder bridge on battered round-ended piers of bull faced granite coursers. Convex approach walls. Iron horse shoe arch with inscriptions to both faces on S approach (see notes). Simple die blocks and wing retaining wall to N. Ornamental cast iron handrail to carriageway.

Statement of Special Interest

This large and particularly ornate bridge was the main approach to the main Mar Lodge complex. The decorative cast iron balustrade and sturdy granite piers give the bridge a distinctive appearance, which is further enhanced by the horse-shoe arch to the S. The present bridge replaced a timber and stone bridge destroyed in the Muckle Spate of 1829, and some of the cast iron super structure, notably the decorative balustrade, may date from the previous bridge. The horse shoe arch bears the inscriptions 'Edward VII, 1905', and 'Queen Victoria, 1848' and is a significant landscape feature.

References

Bibliography

Older bridge shown on 2nd Edition Ordnance Survey Map (1899-1901). F Jamieson, 'Mar Lodge Estate, Vol I, Documentary Research' NTS, (1998), pp77, 79-80.

. NB Planning and Architecture 33 Ellieside, Lintmill, Cullen, Moray, AB56 4XQ, 01542 842847 [email protected]