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Article from Restorica Vol. 17 - No. 34 - November 1976 - pp 49-50
Like old soldiers, it seems, old buildings don't die, they just fade away. But unlike old soldiers buildings can be restored to their former glory. Just such an example is Kimberley's City Hall. Since the completion of new municipal offices in the city, the old hall had been unused and uncared for, its shell crumbling and cracking. This is the story of the saving of this historic structure by the use of complex drilling and pinning techniques. A campaign was mounted to save the building and, when restored, to have it declared a national monument. But structural damage was severe and the materials dry and powdery. Using a dry diamond drilling technique and a method of pinning common in mining, the structural damage has been halted and the remainder of the renovation programme can be completed.
Kimberley began in 1871 with the discovery of the first diamond on Colesburg Kopjie which eventually became the Big Hole. A tented town mushroomed around the deposits, at one time housing almost two hundred thousand people. Unlike many 'rushes', the Kimberley diamond mines didn't run out and today the town is still alive with a population of about 125 000 people.
When a large number of people gather together a certain amount of organisation naturally occurs. In Kimberley's case, it began with the formation of Diggers' Committees which grew into the Town Council. Naturally the Town Council must have a building in which to hold meetings and house the staff. So it was in Kimberley but the first town hall did not last very long. A fire in 1898 destroyed most of the building and the twenty years of records in it.
However, it did not take long for a decision to be made to build a new Town Hall and designs were called for, a prize of £100 being offered for the design selected. The design chosen was by a Mr F Carlstairs Rodgers, a Kimberley architect. On Wednesday 16th November 1898 His Worship the Mayor, Mr Moses Cornwall JP, laid the foundation stone and the building was completed only ten months later.
Until about five years ago  the building was in daily use, becoming a City Hall when Kimberley achieved that status in 1913. As the city grew the functions of the municipality became more complex, requiring more and more staff, until a new complex of buildings was necessary. Since then the building has been unused and virtually unattended.
It was eventually decided that the building should be renovated and given to the nation as a national monument. The renovation is now well under way  but whether the Monuments Council will accept the building depends on many meetings yet.
The major problem was the outside structure. Built of locally made bricks and mortar, the building had suffered over the years from the extremes of temperature found in Kimberley and the general weathering of the materials. The facade above the Corinthian columned entrance, was threatening to fall into the main street and the back left hand corner into the market.
It looked an easy job at first sight. Just drill some holes in the facade and put in tie rods to hold in the front and strap the corner to prevent the crack spreading. This would have worked for most buildings. Here it would have aggravated the situation. The bricks are old and crumbling, and in places the mortar can be pulled out by a finger. Conventional techniques for drilling therefore could not be used. The vibration from a percussive drill would probably have caused the building to fall down and the water from a diamond drill would have washed the mortar from between the bricks with the same result.
Kimberley is still an active mining town and miners are constantly using their ingenuity to devise ways of holding up roofs and walls of tunnels and some very sophisticated techniques have been developed. Engineers of De Beers Consolidated Mines were therefore consulted and they suggested that if holes could be drilled length ways through the walls to beyond the crack, steel rods could be inserted and grouted into position with a fast setting resin such as is used in the mines to brace tunnel roofs. But how to drill the holes - that was the question.
Obviously it had to be with diamond drills to minimise the vibration, give accurated holes over lengths up to 4,5 m and clean holes to minimise the amount of work to make good after drilling. The De Beers mines have a very close relationship with the Diamond Research Laboratory in Johannesburg where intensive research has been carried out into most kind of drilling. The contract was made and the problem presented. But even the engineers at the DRL had not tried this kind of drilling, especially over distances of 4,5 m and accurate to within 4 deg. However they had a few ideas and all they could do was try them.
A team comprising one miner and two engineers from the DRL was formed. The mine would supply compressed air to operate the drill, give high pressure air to be used to cool the drill and remove the debris formed in drilling, so that water need not be used. The DRL would supply the diamond drill, bits and rods. Scaffolding was erected and the job begun.
The facade was the first to be tackled since the holes were short and directly through the wall. Tie rods were then to be fitted and the facade braced back to main beams. At first a surface set drill bit was used on the assumption that the particles would be coarse and the larger size of diamonds would give more clearance to remove the dust. But this bit was subjected to constant core jamming which prevented progress of the bit and caused a considerable amount of over-heating. The heat generated was sufficient to cause the diamonds to start to carbonise and the metal matrix to blue.
A thin wall bit impregnated with 18/20 US mesh De Beers EMB-S natural diamond, was fitted and cutting rates improved considerably and the overheating problem was aleviated. In all, eight holes were drilled through the 0,5 m thick wall, each taking about half an hour including the time taken to move the machinery. The drill used for these was a low powered, air-driven, mine drill.
This part of the exercise was extremely useful in that it was possible to determine the power that would be required to drill the long holes at the back of the building and the best type of bit to use. The low powered mining drill supplies by the mine could not be used and the DRL engineers therefore brought from the laboratory a 10 hp pneumatic drill which turned the bit at 200 rev1min. It was also decided that the air to the bit could be increased if a core breaker were fitted. This would not only prevent jamming but reduce the need to pull the rods.
From here on, the drilling was very fast, accurate and almost vibration free. Twenty-three holes were drilled to beyond the crack, these varying in length from 3,2 m to 4,5 m at an average speed of an hour per hole including the time taken to resite the drill. Eight 2 m long holes were then drilled in the back wall at 90 deg to the long holes to provide extra support. This particular rig was secured to the scaffolding and the drill rods were inserted through the machine since drawing of the rods was not necessary. But the drilling was not without problems. Loose bricks in the middle of the wall sometimes dropped into a cavity, blocking the drilled hole, necessitating redrilling until the brick was completely broken away. At other times the building looked as if it was on fire, the high pressure air finding its way out of the cracks and carrying dust with it.
When the holes were completed a crew from the mines took over to insert and secure the rods. The holes were blown out to remove the last of the debris and the rods inserted. The polyester resin was mixed and pumping began. This operation had to be done very quickly since the resin hardens to a gelled condition in only forty minutes. Only time will tell if the operation has been a success but hopefully the combination of diamond drilling, steel rods and fast setting resin will prevent any further damage being suffered by this historic building.
—Construction in Southern Africa, March 1976
(LRIBA nom papers 1925; WW in Arch 1914; Restorica Nov 1976:49-50; drawings dated 1906 see collection JOUBERT, OWENS, VAN NIEKERK, WATT & PARTNERS, Kimberley)
These notes were last edited on 2021 02 03
All truncated references not fully cited below are those of Joanna Walker's original text and cited in full in the 'Bibliography' entry of the Lexicon.
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