dudley zoo concrete jungle

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36 SPAB Summer 2017 I t is unlikely that a new zoo would open now, but if one did how many would turn up over the first weekend? Probably not the numbers that turned up 80 years ago, when Dudley Zoo opened on the Whitsunday weekend and the Dudley Herald reported: “Bewildering Bank Holiday Traffic Scenes on Castle Hill. Estimated 150,000 visitors – 50,000 admitted”. By the end of 1937 the zoo had had nearly 700,000 visitors and most would have come to see the animals and the 16th-century ruins on the top of Castle Hill. The third attraction was the buildings themselves and for many it is likely to have been their introduction to the Modern Movement. While de-industrialisation has meant the area is no longer “black by day, red by night”, the zoo continues to be the main attraction in this part of the West Midlands. Recent works, aided by the Heritage Lottery Fund, have repaired a number of the reinforced concrete buildings and structures – all listed Grade II* or II – so that they are once again an attraction in their own right. The story of the zoo begins in 1935. Castle Hill was owned by the 3rd Earl of Dudley, William Humble Eric Ward, and he formed the first board of directors of the Dudley Zoological Society Limited with a local businessman, Ernest Marsh, and William Frank Cooper. Captain Cooper – of the jams and marmalade family – was looking to close his zoo in Oxford and find a new home for his animals. The Superintendent at London Zoo was appointed as their advisor and he introduced the Tbilisi-born architect Berthold Lubetkin whose practice, Tecton, had recently designed the Gorilla House and Penguin Pool in London. The structural engineer at London Zoo was Ove Arup and at Dudley he was the director responsible for designs and tenders for the contractor JL Kier and Co Ltd. To have the zoo open in the spring of 1937 CONCRETE JUNGLE Dudley zoo Innovative repairs to the concrete 1930s ‘Tecton’ structures at Dudley Zoo fascinated delegates on a recent SPAB Repair course. We invited structural engineer Stuart Tappin, whose practice Stand Consulting Engineers worked on the zoo’s remarkable architecture, to write about the project

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Page 1: Dudley zoo CONCRETE JUNGLE

36 SPAB Summer 2017

It is unlikely that a new zoo would open now,but if one did how many would turn up overthe first weekend? Probably not the numbersthat turned up 80 years ago, when Dudley Zoo

opened on the Whitsunday weekend and theDudley Herald reported: “Bewildering BankHoliday Traffic Scenes on Castle Hill. Estimated150,000 visitors – 50,000 admitted”. By the end of 1937 the zoo had had nearly700,000 visitors and most would have come to seethe animals and the 16th-century ruins on the topof Castle Hill. The third attraction was thebuildings themselves and for many it is likely to

have been their introduction to the ModernMovement. While de-industrialisation has meantthe area is no longer “black by day, red by night”,the zoo continues to be the main attraction in thispart of the West Midlands. Recent works, aided bythe Heritage Lottery Fund, have repaired a numberof the reinforced concrete buildings and structures– all listed Grade II* or II – so that they are onceagain an attraction in their own right. The story of the zoo begins in 1935. Castle Hill

was owned by the 3rd Earl of Dudley, WilliamHumble Eric Ward, and he formed the first boardof directors of the Dudley Zoological Society

Limited with a local businessman, Ernest Marsh,and William Frank Cooper. Captain Cooper – ofthe jams and marmalade family – was looking toclose his zoo in Oxford and find a new home forhis animals. The Superintendent at London Zoowas appointed as their advisor and he introducedthe Tbilisi-born architect Berthold Lubetkin whosepractice, Tecton, had recently designed the GorillaHouse and Penguin Pool in London. The structuralengineer at London Zoo was Ove Arup and atDudley he was the director responsible for designsand tenders for the contractor JL Kier and Co Ltd.To have the zoo open in the spring of 1937

CONCRETE JUNGLEDudley zoo

Innovative repairs tothe concrete 1930s‘Tecton’ structures at Dudley Zoofascinated delegateson a recent SPABRepair course. We invited structuralengineer Stuart Tappin,whose practice StandConsulting Engineersworked on the zoo’s remarkablearchitecture, to writeabout the project

Page 2: Dudley zoo CONCRETE JUNGLE

SPAB Summer 201737

The bear ravine before (above): ‘The initial review of the bear ravine had identified significantstructural issues with the cantilevered viewing platform. The bear ravine before (below): Mostdefects were as a result of inadequate concrete cover to the steel reinforcement. This had led theto corrosion of the bars and extensive areas of spalled concrete. Along with the corrosion of thebars there was an unsettling “bounce” when walking at the end of the platform and a number ofcracks due to structural movement.’

The bear ravine after (above and top): ‘Thisplatform is the most complex structural elementat the zoo, but by establishing how it stands upand understanding the causes of the damage wewere able to determine where a “helping hand”was required and target works to those areas.’

Page 3: Dudley zoo CONCRETE JUNGLE

Right: Dudley Castle, viewed from thezoo. Work went on around the merkats toavoid any disruption to their breeding regime

SPAB Summer 2017 39

Dudley zoomeant that the design and construction had toproceed at a rapid pace. There were furtherpressures from dealing with the AncientMonuments Department of the Office of Workswhich was concerned about the setting andintegrity of the castle, and Lubetkin’s design kepta respectful distance. There were also unexpectedengineering challenges from the unrecordedtunnels and mines for the extraction of limestoneand coal. All these factors led to much of the finaldesign being carried out on-site by the projectarchitect Francis Skinner and Kier’s residentengineer, Ronald Sheldrake. Inevitably there werecompromises, as we shall see, for both the designand the quality of construction.As reinforced concrete is not usually found on

the pages of this magazine, it is worth brieflyputting the buildings at Dudley Zoo into context.The patent for Portland cement was taken out in1824 by Joseph Aspdin, a mason from Yorkshire,but the UK, in comparison with continentalEurope, was slow to pick up on the possibilities ofthis new material. Further patents, mostly fromoverseas, were taken out during the 19th centuryand into the 20th century that combined concretewith reinforcement in various ways. There werehowever a number of significant early reinforcedconcrete structures in the UK, in particular the six-storey Weaver and Co flour mill built in Swanseain 1897 (demolished 1984) and the Royal LiverBuilding at Liverpool Pier Head that, whencompleted in 1911, was the largest reinforcedconcrete framed structure in the world. Both werebuilt using the French Système Hennebique, butthese were exceptions and the set-up of the UKconstruction industry during the first half of the20th century meant that the majority of largebuildings tended to have a steel frame. Things began to change in the early 1930s

with the arrival of architects, engineers andcontractors from Europe who brought newforms and styles, new methods ofstructural analysis and innovativetechniques to build with concrete. Thepatented systems could not keep upwith these new demands and thestructural design at Dudley wasdeveloped from first principles,albeit with the engineer working forthe contractor rather than as anindependent consultant.In 2011 Stand Consulting

Engineers was appointed as part ofthe design team led by Bryant PriestNewman Architects for the repair andrefurbishment of four of the structures;the original entrance to the zoo, the bear

Page 4: Dudley zoo CONCRETE JUNGLE

SPAB Summer 2017 41

ravine and a nearby kiosk, all individually listed atgrade II*, and the grade II Station Café that nowserves as the main entrance and shop. All were in apoor condition and the bear ravine and kiosk hadboth been out of use for a number of years. As with all types of structures a key part of the

assessment was to understand the cause(s) of thedamage. A building materials specialist, RowanTechnologies, carried out a range of non-destructive and invasive investigations that helpedus to confirm that the majority of concrete was ofa good quality and most defects were as a result ofinadequate concrete cover to the steelreinforcement. This had led the to corrosion of thebars and extensive areas of spalled concrete.Although unsightly the damage to thereinforcement was mostly superficial and it wasonly on the viewing platform of the bear ravinewhere concerns about the structural performancewere identified.As the modern layers of paint were removed

during pre-tender investigations – taking care notto damage the surface of the concrete – a numberof repairs were exposed along with traces of theoriginal painted finish. None of these previousrepairs had addressed the underlying causes of thedamage and consequently they had also failed.SPAB readers will not need to be reminded thatthe use of like-for-like materials is one of the keyprinciples for the repair of historic structures, butuntil recently the majority of concrete repairs werecarried out using high-strength epoxy mortars thatare significantly different to a traditional mix ofPortland cement, sand and aggregate. These modern repair mortars were developed

for utilitarian structures such as motorway bridgesand the relevant British Standard is premised ontheir use. Their application on listed buildings ishowever being questioned by organisationsincluding Historic England, the 20th CenturySociety and ICOMOS. As with more traditional

Dudley zoo

The canopied entrance before: ‘The top of the entrance canopies had never been waterproofed and had been designed with a shallow fall to a smalldrainpipe that ran through the kiosks below, although the majority of rainwater ran over the edge of the roof slabs. The concrete was, unsurprisingly, damp.’

The zoo shop, pictured after the recent work had taken place, was also part of the project

Inside the zoo shopThe zoo entrance, following work

Page 5: Dudley zoo CONCRETE JUNGLE

42 SPAB Summer 2017

Dudley zooforms of construction, a repair that usescompatible concrete will reduce the risk of futuredifferential movement from thermal expansion andcontraction or due to changes in the moisturecontent. In addition, the alkalinity of a cement-based repair can help to protect against futurecorrosion of the nearby steel reinforcement.Finally, for listed structures with an exposedconcrete, a compatible mix will provide a closervisual match to the original fabric. A key aim for the repairs at Dudley was to use

a concrete mix that was similar to the originalconstruction wherever possible. This was fullysupported by the project team and client togetherwith English Heritage, as was, and the 20thCentury Society. Another part of our conservation-based approach was not to repair unless there wereclear signs of damage. This meant, for example,that poorly formed construction joints or localirregularities in the surface from poor compactionof the concrete would be retained as a record ofhow the structures were originally built.A useful aid when assessing historic buildings

is to put yourself in the place of the originaldesigner or builder and then consider how itemslike the methods of analysis and the availability oftools and skills had an influence on what was built.One area where this proved useful was inunderstanding the poor condition of the undersideof the curved slabs to the original entrance. Thereis little information from the 1930s of how thesteel reinforcement was to be supported as theconcrete was placed, but a reference in Cassell’sReinforced Concrete, published in 1920, mentionsthe use of notched timber templates. It notes these“can be removed shortly after the concreting hasbegun, quite a small quantity of concretesufficing to hold the rods in place”. If thismethod was employed the undulating shape ofthe slabs meant it was almost inevitable thatthe bars would slump towards the bottomof the wet concrete and come to rest onthe timber formwork. These bars wouldhave been visible as soon as theformwork was removed and we canonly surmise that the pressure toopen the zoo to the public led toa “make-do” approach of addinga thin render and paint to hidethe exposed reinforcement. In early 2013 trials of the

proposed repairs were carriedout. These explored differentmethods to remove the damagedconcrete, how to deal with thelimited concrete cover to the bars,

an assessment of the amount of water andproportions of the cement: aggregate repair mixand how to match the surface finish. This helped toinform the tender documentation andspecifications were written “from scratch” to coverrepairs in different locations (top, side or soffit)and for different degrees of damage. Tenders wereissued to concrete repair specialists and general

Below: The back cover of the officialDudley Zoo 1938 guidebook

Right: Staff at Dudley Zoodressed in 1930s style to

celebrate the 80th anniversary ofthe opening earlier this year

masonry contractors with experience of concreterepairs. A local firm of stone masons was selectedand the works began in September 2013.Most repairs used a 1:2:4 cement: sand:

aggregate mix to match the original concrete withthe size of aggregate chosen to suit the depth of therepair. The procedure was for the edges of thedamaged concrete to be cut using a small disccutter with the arrises slightly undercut, as for adove-tail joint, to improve the mechanicaladhesion of the repair material. The entire surfaceof the exposed reinforcing bar had to be accessible

to remove rust before an anti-corrosioncoating was applied. All the surfaces werethen covered with a cement slurryimmediately before placing the concrete. Ingeneral, the concrete had a plain finish butthe surface was worked to match theexisting finishes including reproducing thelines of joints formed by the original shutterboards. There were some locations, mostly to the

soffit of the slabs and beams, where a repairusing a thin coating with a traditionalconcrete mix was not feasible. To repairusing concrete would have involved eitherthe removal of all the existing concrete torecast around retained reinforcement orincreasing the thickness of the slab to providean acceptable cover to the bars. Recasting theslabs involved the loss of large amounts oforiginal fabric and had cost and programmeimplications. Thickening the slabs would havehad structural implications due to the additionalweight of concrete and significantly changedthe appearance. As with most conservationprojects there had to be a balance between keyconservation principles like the retention of themaximum amount of original fabric, reversibilityand for the use of like-for-like materials. Aftermuch discussion a 4mm-thick modern renderwas used to repair the soffits with a finishedsurface to match the surrounding boardmarks.

The top of the entrance canopies hadnever been waterproofed and had beendesigned with a shallow fall to a smalldrainpipe that ran through the kiosksbelow, although the majority ofrainwater ran over the edge of theroof slabs. The concrete was,unsurprisingly, damp and atemporary covering was placedover each slab to allow thestructure to dry prior to therepairs. A roof covering has now

been applied to protect the concreteand the painted soffit. The designcriteria included being reversible, the

ability to accommodate thermal movementsand to be visually acceptable from below and

Page 6: Dudley zoo CONCRETE JUNGLE

SPAB Summer 2017 45

above for the view from Castle Hill. The works to the entrance and shop were

completed in time for Easter 2014 and to muchacclaim. The zoo then knew how much moneywas left for the more extensive works to the bearravine and the project team had the benefit of theknowledge gained from the first phase of works.The initial review of the bear ravine hadidentified significant structural issues with thecantilevered viewing platform. Along with thecorrosion of the bars there was an unsettling“bounce” when walking at the end of theplatform and a number of cracks due tostructural movement. The tender allowed tostrengthen the platform by replacing all theconcrete to the parapet with additionalreinforcement alongside the existing bars, andadditional reinforcement to the top and bottomof the slab. A key difference was that the contractor for

the entrance and shop was no longer involvedbut their foreman, Carlo Diponio, along with twoapprentices being trained in concrete repairs aspart of the grant from the HLF, became directemployees of the zoo. One indicator of thesuccessful outcome of the works was that Carlowas a winner in the Outstanding Contribution toHeritage category for the 2016 Historic EnglandAngel Awards. Once the works began it found that the bear

ravine concrete was in a much better conditionthan had previously been anticipated and weworked closely with the on-site team to repairrather than rebuild the parapet. The quality of therepair to the corrugated finish of the parapet wallswas a major achievement and the attempts byvisitors during a number of open days to match thefinish demonstrated the skills that are needed tosuccessfully repair concrete. We also explored analternative to the tender allowance of additionalmesh reinforcement within a high-strength renderon the top and bottom of the platform. Thisplatform is the most complex structural element atthe zoo but by establishing how it stands up andunderstanding the causes of the damage we wereable to determine where a “helping hand” wasrequired and target works to those areas. Narrowcarbon-fibre sheets, each 1mm thick, were bondedto the concrete in these areas to provide theadditional strength without any significant changein weight or appearance. Once again theconservation arguments were debated beforehand,balancing the use on a modern material against thewidespread replacement of original fabric or achange of appearance. Once the repairs werecomplete there was a noticeable reduction in thebounce when walking on the platform.The structural repairs to the nearby kiosk were

more straightforward. The base of each hollowsteel columns had completely corroded and steelsleeves were welded around the base to reinstatethe original support. These works were completed

Dudley zoo

BERTHOLD Lubetkin was a Russian émigré architect who pioneered modernist design in Britain in the 1930s. Probably born in Tbilisi, now the capital of Georgia, Lubetkin practised architecture in Paris in the 1920s where

he associated with leading figures of the European Avant Garde, including Le Corbusier.Emigrating to London in 1931, he set up the influential architectural practice Tecton. The first Tecton projects

included landmark buildings for London Zoo, notably the gorilla house and penguin pool. Tecton was also commissioned by London Zoo to design buildings for its reserve park at Whipsnade and to

design a completely new zoo at Dudley in the West Midlands. Dudley Zoo consisted of twelve animal enclosuresand was a unique example of early Modernism in the UK. All of the original enclosures survive, apart from thepenguin pool, which was demolished in 1979. According to the 20th Century Society: “Encapsulated in the playfulpavilions at Dudley is a call to remember the higher calling of all architecture, embracing not just material needsbut also the desire to inspire and delight.”

early in 2015 and the on-site team then moved onto the sea lion pool and the former reptillary. Nowhome to meerkats this is the only enclosure not tohave been painted. The work to repair the concreteand the highly skilled operation to match theexposed-aggregate finish had to be carried out instages with the meerkats remaining in place toavoid any disruption to their breeding regime. These repairs now form an important part of

the history of the zoo and an area in the shop hasan interpretive display that tells the story of thezoo and its buildings. As the conservation-basedapproach to the repair of historic concrete is still atan early stage the works to the bear ravine are now

being monitored by Historic England. The resultsto date are encouraging and should, for the firsttime, provide reliable information on theperformance of traditional concrete repairs. This isimportant as the number of listed reinforcedconcrete buildings and structures continues toincrease. l Stuart Tappin is a structural engineer with hispractice, Stand Consulting Engineers, who arebased in a 1960s listed building. He is a memberof the 20th Century Society Casework Committeeand the UK representative for the ICOMOSInternational Scientific Committee for 20thCentury Heritage.

LUBETKIN AND TECTON...

The penguinpool atLondon Zoo

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