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STONE STABILISATION WORKSHOP “The Lake Johnson Agreement” 2nd & 3rd December 2003

Paper for the National Historic Heritage Workshop 2004. y Jackie Gillies.

f a bomb had dropped on Lake Johnson near Queenstown in early December last year, the idal wave would have wiped out a rather gorgeous little stone building typical of Central tago vernacular –

Fig.1 The “Dairy” at the Gillies-Goldsmith House, Lake Johnson.

s well as more than 20 of New Zealand’s keenest stonework enthusiasts, including a umber of New Zealand’s real stonework heavyweights. Fortunately for New Zealand the ingers on the button were looking the other way that day - and all were spared.

he get together was organised by Paul Mahoney and the purpose was to bring together a ide range of interested parties to co-operatively develop a set of guidelines for the

ustainable conservation of Central Otago’s vernacular stone buildings.

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Fig.2 Paul Mahoney, working hard organising the day’s programme.

Central Otago stonework typically, demonstrates distinct style, construction and conservation requirements, as well as particular issues affecting its long-term retention. There has been, in the past, occasional – vociferous – debate by those closely involved about how these buildings should be maintained, repaired or re-used and the intention of the workshop was to find a mutually acceptable and agreed approach for those buildings requiring work in the future. The group attending the workshop included several South Island DOC rangers with particular interest or expertise in stonework, several representatives of the Historic Places Trust in the South Island, as well as the South Island’s best conservation stone mason, Keith Hinds, members of the public with particular interest in these buildings, archaeologists, conservation architects and Lou Robinson – in a class of his own.

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Fig 3. The group outside the Dairy at Lake Johnson.

I think we thought a straightforward document would emerge which would set out the issues and propose solutions for each circumstance. As always, of course, we discovered very quickly that such a simplistic approach was not how it was going to work. Having said that though, I think the underlying purpose of the workshop was achieved – to explore the issues affecting the conservation of Central Otago stonework and understand them so that appropriate solutions to each individual case could then be found. Definitions First of all it may be helpful to define what we mean by “Central Otago stonework”. Such stone buildings share a number of common characteristics and these are,

They are generally small scale – due to the limitations of the locally available materials and the pockets of their builders, a clear vernacular style – derived from the influence of the predominant immigrant populations from Scotland, Australia, America and Ireland.

They can also be described as Permanent or temporary;

Fig.4 The toilet at Ah Lum’s cottage, Arrowtown Chinese Mining Village.

Stonemason or amateur built;

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Fig.5 McNeill’s cottage, Queenstown.

Dry stone or random stack flush face with mud mortar and

Ruins or a living building.

Fig.6 Lindis Hotel ruin.

Process Inventory In order to fully protect these buildings it is important to know where they are and how many still exist. Unfortunately it seems that no thorough inventory exists. Many buildings lie forgotten in the back of high country stations or deserted gold mining settlements and as the local knowledge about these places slowly disappears, the chances of preserving them also disappear. The knowledge that we have is incomplete and comes from High country Tenure Review surveys, local DOC surveys or from some local authority sources, but it is not enough. Perhaps what we need is a postgraduate thesis or dissertation entitled “Vernacular

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Architecture of Central Otago” which would include a really thorough survey of all that remains. Research and Analysis. When a particular building or ruin is being investigated, the most important part of the process is the initial research aimed at understanding the history, the significance and the issues affecting the conservation of the place. This might take the form of a conservation plan, a conservation statement or a building report. The DOC model Conservation Plan and Standard Operating Procedures are an excellent example of such an analysis providing logical and linear appraisal of all the factors which will influence decisions about future action. This analysis should result in clearly articulated conservation policies with reference to relevant standards such as ICOMOS New Zealand as well as detailed policies regarding methods and techniques required and sometimes what specialised training might be required. Proposals Any proposals which follow will be less intrusive and will have less impact on the place if they are based on such an analysis. Not only that, but communicating the proposals to the public becomes more straightforward if they can be shown to have been based on a thorough understanding of the place. HIA Sometimes it is helpful to use a tabulated Heritage Impact Assessment to check the impact of the proposals against the identified significance. This was formulated by Kate Clark of English Heritage and has the advantage of splitting the proposals into “bite-size” pieces, allowing the potential impact of each element to be visualised and assessed. PROPOSED WORK

SIGNIFICANT FABRIC AFFECTED

RATING REASON FOR SIGNIFICANCE

POTENTIAL IMPACT + or -

MITIGATIONMEASURES

Communication However it is presented, communication with local interested parties such as land owners, historical groups, neighbours, the Historic Places Trust and the local council throughout the process is extremely important. Many of these buildings are of more significance today as key elements in the landscape than as functioning living buildings in private ownership and their importance to the wider community therefore is great – there is a sense of ownership by the wider community almost. Lack of communication at an early stage can cause severe hiccups later on if the reasons for certain decisions are not understood or communicated well. Not only that but an opportunity to incorporate individual local knowledge may be lost.

Practice The practical conservation of Central Otago stonework includes some issues which are common to all stone buildings as well as some that are particular to the type. Like Materials Among those issues common to all stone buildings is the importance of repairing like with like. Stone This includes matching the stone used where it is necessary to replace some parts, not only in a matching stone type but if possible from the same source, which in Central Otago usually means from the paddock around it.

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Why anyone would want to do this is a mystery to me. Mortar Secondly, the choice of mortar material is extremely important, whether the original was simply mud, mud with lime added or straight lime mortar. We visited Thurlby Domain Stables in Speargrass Flats Road, currently being restored by Vicki and Revell Buckham. The stonemason is Keith Hinds and he

has re-instated part of the front wall which was removed to allow access for tractors in the 1960s as well as recreating two stone gables visible in early photographs.

Fig.7 Much Wenlock Church, Shropshire, UK.

He was able to use most of the original stones because they had simply been thrown into a corner of the site.

Fig.8 Hallenstein’s Stables, Thurlby Domain, Speargrass Flats Road, Queenstown.

He also used mud mortar obtained by excavating sub-soil from the adjoining paddock, sieving it and mixing with water to a viscous consistency with extremely good adhesion characteristics. The original mix appears to have had a small proportion of lime added, but the new was work was in a pure mud mix.

Fig.9 Detail of Stables wall, showing two skins of stonework with mud mortar between.

The original mix was probably a “hot mix” whereby burnt lime stone chips, quicklime, is mixed directly with the damp binder, in this case mud, but could also be damp sand, slaking and mixing as it goes.

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This was a very common practice traditionally. You can usually recognise a hot mix by the odd small white lumps of unslaked lime which remain in the mortar. Most lime mortar or lime plaster was originally made using slaked lime prepared on site as a putty or as a hot mix as just described. But today in New Zealand it seems that dry hydrated lime or hydraulic lime are used because there is no commercial source of slaked lime putty, or “fat lime”.

Fig.10 Bagged Hydraulic Lime.

There was considerable discussion about this at the workshop, and, in what may be a first in legal history, may result in the Historic Places Trust and the Department of Conservation being cited in divorce proceedings. How? Well, Guy Williams from the Dunedin office of the HPT put forward a proposal that local branches could get together and make slaked lime putty and sell it as a fund-raiser. It can be made very simply from quick lime chips which are added to water, allowed to react and then stored until required, the longer the better. Using either powdered hydrated or hydraulic lime or mixing up the slaked lime putty on the day it is needed are not satisfactory options if the intent is to match original mortar or plaster mixes. And the alternative – of having ready-made slaked lime putty available for use whenever it is needed – is so easy to achieve. DOC is in an excellent position to set up a works and start stockpiling supplies for all its jobs. Now where the divorce comes in, is that this talk by Guy completely turned my head. He was right – it was so easy to make the stuff, and so important that the right stuff was made someone was going to have to make it – how about me?? So while in the UK last month for my York MA graduation, I spent a week visiting 4 of the 22 or so commercial lime-putty producers in England in order to understand the important differences between making enough lime in my garage for one job and making a consistent supply of putty for sale. 8

Fig.11

Finished Lime Putty, showing consistency of thick yoghurt

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Fig. 12

Truck mounted concrete mixer used to slake large quantities of burnt lime.

Fig. 13 The slaked lime is poured into this large vat.

Fig. 14 The slaked lime is strained through various grades of sieve to remove impurities or unslaked particles.

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Fig. 15 The strained lime putty then settles for about 3 weeks and excess water allowed to drain away.

Fig. 16 Close-up of finished lime putty before packaging in 20l tubs.

As a result, I am now on the look out for a second-hand concrete mixer – the sort that goes on the back of a lorry - to slake large quantities of lime in, and a divorce lawyer because my husband thinks his car should go in the garage, not my concrete mixer! Watch this space! Back to earth- Ruins Sadly many of Central Otago stone buildings remaining today are in ruins. They were erected quickly at the end of the 19th C for particular purposes such as musterer’s huts, gold miners cottages or hotels, or agricultural uses such as stables, barns etc and many of these purposes have now lapsed. As result, the buildings are abandoned, often in remote locations. The roof falls in or the iron is taken off to be used somewhere else and the unprotected stonework very quickly crumbles away. The hotel in Skippers is a good example where the ruin was recognisable as a building with walls, doors and windows but no roof some ten years ago, but is now no more than a pile of stones.

The range of treatments for ruins is different to those for living buildings, where weathertightness and use or function are important factors. Here the philosophical issues questions are

-are the ruins to be allowed to crumble – a sort of dust-to-dust approach? -are they to be stabilised as a ruin?

-or are they to be restored to a living functioning building? The decision must be based on the analysis described earlier. Once the site is fully understood along with the reasons for its significance, it becomes clear which approach is the most appropriate. The Lindis Hotel is another example but one which DOC hopes to stabilize before any further deterioration occurs.

Fig. 17 General view of Lindis Hotel.

As you can see, the building is a ruin, but it is still quite easy to visualise it as a complete building. Location of building, gold mining area on Lindis River West wall fell in last earthquake

Fig. 18 Lindis Hotel, showing West wall, fallen in last earthquake.

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Rebuild from evidence Cap remaining wall heads to prevent water washing away the mud binding the two skins of stonework together

• Guy William’s lime coping proposal – remove

mortar coping sloping down to each edge, re-beto wall of compatible material with minimal vis

• Stone coping • Lead flashing • Turf (UK)

Biological Action Another issue is that of biological growth on the stonewruins. These include lichens, mosses and bryophytes. It has been proved that lichens can have a detrimental esurfaces of stonework due to an acidic action of their roBut stacked schist stone is unlikely to be affected by thencrusted wall is very appealing. Mosses and bryophytes will have less effect again and systems only extend about 5mm into the mud or lime mto protect the joints from excessive freeze-thaw cycles

Fig. 19 Lindis Hotel, showing 2 skinsof stonework and uncapped, vulnerable wall-heads.

top layer of stone, lay solid lime d top stone. Effect – weathering cap ible change.

ork which can affect the stability of

ffect on flat or intricately carved ot system.

is and the visual effect of a lichen

may even be beneficial. Their root ortar joints and they may in fact help

or erosion from wind and rain.

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Woody plants are a hazard though and these need to be removed while still quite small, up to 6” long by cutting them off with secateurs at their bases – not by pulling them out as this may damage the mortar joints even more. Finishes One of the most difficult and contentious issues regarding the conservation of Central Otago stonework involves the decision as to the final finish. These buildings were built of random stacked stone usually with mud mortar and often with a weathercoat of lime plaster over the exterior surface. Similar construction types exist in England too.

Fig. 20 Much Wenlock Church, Shropshire, UK, showing traditional rubble wallwith lime plaster coating.

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Fig. 21 Much Wenlock Church, Shropshire, UK, detail of plaster coating.

Over the years this weathercoat tends to fall off – more at the bmuch of the time, than at the top, but often it is all lost. As a rebuildings today is of stacked exposed stone with deeply recesse

Fig. 23 The Dairy, Lakeof new house.

FigDeintof g

Fig. 22 Much Wenlock Church, Shropshire, UK, close-up of plaster showing three coats.

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ase where it remains wet sult the perception of these d joints.

Johnson, now part of interior

. 24 tail of Dairy, showing act plaster coating at top able.

In repairing and stabilising these buildings should we simply reta

– or should we reinstate the original weathering coat, being true t

Part of the answer lies in the outcome of the original analysis carare the factors which make this building significant?

– and part of it lies in the outcome of the public consultation – wthe factors which make the place significant.

This decision is never easy, because the radical changes made byreplastering can change the appearance to an unacceptable extent

FigThconbaswe

FDnM

Fig. 25 Detail of Dairy, showing erosion of plaster coatingat base of wall.

in them as we found them

o the original technology?

ried out at the start – what

hat the community feel are

large-scale repointing or .

. 26 e Dairy, showing trasting new pointing at e of wall after 9 years of

athering.

ig. 27 etail of inappropriate, on-traditional repointing, uch Wenlock, Shropshire.

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Wouldn’t it be better if more frequent repairs of a minor nature could be carried out much as they always would have been in the past, which allows each wave of repair to weather-in naturally, and avoid the once in a blue moon radical makeover. Earthquake strengthening. Earthquake strengthening of old stone buildings is often cited as the factor which makes re-use or even stabilisation impractical or uneconomic. However, if the building is assessed by an engineer with specific knowledge of historic structures and a proper analysis is carried out, then a suitable and cost effective solution should be possible. At the Lindis Hotel for instance, one whole wall has fallen over, probably in last year’s major earthquake, all the stones lying as they were in the wall, but now laid out on the ground. This makes it relatively easy to rebuild the wall pretty much as it was, having marked and recorded each stone.

Fig. 28 Lindis Hotel, showing earthquake damaged wall.

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Fig. 29

Hallenstein’s Stable showing rear wall after earthquake movement.

Elsewhere, walls have bulged or are leaning and will require different levels of intervention to stabilise. Whether or not specific structural measures are proposed, the first defence against earthquake damage of stone buildings is good maintenance. If the top of the wall is weathered and the joints kept pointed and the junctions between major structural elements are sound, then the building will be able to withstand higher levels of earthquake pressure.

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Having said that, Lou Robinson pointed out to the workshop that with respect to stone ruins in an isolated windswept location, the effects of wind pressure are likely to be more damaging than and more frequent than the risk of an earthquake. As a result it was recommended that stone ruins in such locations should be propped from an early stage. Conclusion The process of dialogue and shared expertise begun at the workshop continues. The proceedings of the workshop will be circulated to all present for comment and amendment and with luck, will form the basis of a continuously evolving co-operatively agreed strategy for the conservation of Central Otago stone buildings from now on.