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Keeping faith with history

CONCRETE - Goldthorpe Church: The hidden secrets of an historic concrete church in Yorkshire turned routine repairs into a major technical challenge. David Hayward reports.

Whenever Andy Came's travels take him near the Yorkshire village of Goldthorpe he detours to the local parish church. And he does not anticipate omitting this little diversion from his route for several years to come.

As regional director of specialist contractor Concrete Repairs, his current visits involve supervision of the refurbishment of this unusual concrete church. But for some time after the £260,000 worth of repairs are complete this Easter, he will return regularly to the church just to stand and stare.

Came will not be enjoying an engineer's ego trip though, admiring work well done. He will be making sure the church has not changed colour.

This colour check on the exposed aggregate concrete exterior is just the latest episode in the history of a locally loved, but somewhat bizarre building.

As arguably the UK's earliest allconcrete church, the Grade II listed structure is a prominent landmark - both physically and historically.

The church was built by local benefactor Lord Halifax to enhance the drab mining village it served and - in the shortest possible time - provide a much needed place of worship using the new fast build material then called ferroconcrete. It was also designed to withstand the local mining subsidence that Lord Halifax' mines were mainly responsible for creating.

But its controversial rough cast finish - sporting a range of pebbles up to 150mm - plus widely varying concrete mixes and textures mean that Goldthorpe Church is of national importance.

'It is a folly with magpie attractions for eccentric and irregular features that help it exhibit its own construction technique, ' says Andrew Wiles, director with architect Wiles & Maguire. 'This church is a nationally important building that has largely been overlooked' (see box).

Goldthorpe's history is also of acute importance to Came, for his nine month concrete repair contract is far from straightforward.

Breaking out and patch repairing some 20m3 of heavily spalled concrete, attacked by acid rain probably emanating from nearby Sheffield steelworks, would, for Came's company, normally be no problem. But with English Heritage demanding a perfect colour and finish match with the original yellow texture, routine became a major challenge.

'We were asked to match the original, so we said 'what original', ' Came recalls. 'Cement and sand content varies even within individual pours, while poor compaction resulted in widely segregated aggregate finishes.'

'We rejected current concrete mix specifications, based largely on proprietary pre-blended bagged materials, and went back to the basics of 1960s real site mixes, ' he adds. 'It took ages to source the right materials and then 30 trial mixes to get the colour and texture exactly right.'

A nationwide search for sand and aggregate matches ended - perhaps unsurprisingly - back with the local builders merchant. Standard ordinary Portland cement provided the best texture, though virtually all additives were ruled out as they affected colour.

But the real challenge came with mix control. The numerous trial mixes experimented with combinations of material and coloured dye content, with each sample left on site for a month to monitor colour change.

And with retarder-coated shutters struck after just 12 hours, the exposed aggregate finish was achieved by brushing off the outer few millimetres of soft laitence.

The final mix was a one part cement, two sand, four coarse aggregate combination, with a 0.4 water/cement ratio and only yellow dye, plus chemical waterproofing, additives. But even with the site mixer churning out the exact colour, the repairs' challenge was far from over.

Supporting the church's 200mm thick concrete walls are 20 integral, 450mm deep, rectangular columns running full 9m height. There were nearly as many different colours and textures in the protruding external face of each column as there had been concrete pours.

So the only way to provide colour consistency during repairs was to cut back most of the columns by 130mm to lie flush with the wall and then rebuild the outer section. This revealed one of the church's less attractive features.

The contractor discovered that column reinforcement consisted only of single maximum 25mm diameter mild steel corner bars with no link steel and the rebar stopping seemingly at random without lapping or any continuity. Wall steel consisting of a single central mat provided equally poor reinforcement.

'Today we would call this reinforcement little more than anti-crack steel and the entire church is really acting as a mass concrete structure, ' states Came.

The ramifications of this discovery affected not so much the 47m long church nave, where new rebar has been added to rebuilt column faces and wall patch repairs - but more crucially the 19m high bell tower, topped by an open belfry and ornate clock.

The complete 5.5m square tower had been rendered with gunite in 1958 and, with English Heritage happy to leave it so, the contractor's task was to have involved simply removing defective rendering and providing a new sprayed concrete finish. But then Came's team got out their testing hammers.

'The tower looked OK from the ground but a hammer test, and then gunite removal, revealed a fair mess, ' Came recalls. 'Large hollows behind the render, with the original corroded concrete not sufficiently cut back, meant that deterioration had continued unseen for decades.'

The major surgery needed, plus the lack of effective reinforcement - with belfry columns facing up to 75% loss of section - left the tower's upper half structurally suspect.

Engineers considered total demolition and rebuild. But the chosen solution of strengthening the top section with an internal 10m high steel frame, and then repairing the original, at £80,000 worked out 60% cheaper than demolition.

While main contractor William Birch continued with more general repairs - primarily a new tiled roof - work on the tower stopped, delaying the overall project by some 10 weeks. But no one was blaming Came's team, and resident architect Wiles acknowledges a challenge overcome.

'Other tenderers said it was impossible to match the original finish and refused to tender on our terms, ' he says. 'But it is now very difficult to tell new concrete from old, and repair quality is outstanding.'

Collector s items Goldthorpe Church is described by the architect overseeing repairs, Andrew Wiles, as a folly with magpie tendencies.

It was the creation of two men, both then in their 70s: local benefactor Lord Halifax and eminent retired architect Alfred Nutt, onetime consultant at Windsor Castle.

Built in 1914, the Grade II listed church is probably the first, and still one of the few, to be built entirely from reinforced concrete - a material then barely 20 years old. Everything is concrete;

structure, altar, font and even the full size crucifix.

But it is said the two elderly creators were not trying to be pioneers; it was more a case of businessmen making use of a new material claimed to be quicker and cheaper to erect than brick, as well as being able to withstand the differential settlement likely to result from local mining activity.

Foundations did include a concrete raft, but, only 150mm thick and poorly reinforced, subsidence has broken its back triggering large near vertical settlement cracks in church walls.

The magpie reference reflects the structure's collection of early concrete 'attachments'. These include poor compaction with larger aggregate settling to the bottom of pours; very obvious shutter lines and pour changes, plus seemingly random mix control even within a pour.

Repair supervisor Andy Came of Concrete Repairs, reckons there was no real reinforced concrete design, with discontinuous rebar having little structural value other than crack control. Site engineers also cite the legend that Lord Halifax may have been influenced in his choice of concrete by a contractor more experienced as a builder of monuments and sculptures - all cast in concrete.

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