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If new Battersea Power Station hopeful Treasury Holdings feels the need for a reality check on its grandiose development plan for the site, it鈥檚 not difficult. All any of the staff has to do is scale the side of the huge brick structure to a platform at the base of one of its four massive chimneys, where you get a fantastic bird鈥檚 eye view of the whole site and London beyond. Away from the building, things look rosy enough; to the east, west and south there are large expanses of empty space, punctuated only by weeds and grass, which are ripe for developing Treasury Holdings鈥� ambitious Rafael Vi帽oly-designed scheme (see box, below).

But the closer you to this vantage point you look, the worse things get. You look straight down into the huge, roofless boiler house below, and see how badly corrosion has eaten away at parts of the building鈥檚 steel frame. The days of rock concerts inside this massive space are long gone; a 30m exclusion zone has been placed around each of the four big chimneys because of the risk of bits falling off and injuring people below. Standing next to the base of the chimneys, it鈥檚 obvious why. The concrete is riddled with cracks and the rebar has corroded to the point that the only option is to demolish and rebuild the chimneys. The turbine halls and annexes on either side of the boiler room still feature roofs with central glazing but glass is falling into the space below.

Tackling these not inconsiderable problems is Treasury鈥檚 first job. The initial phase of its scheme is centred on the existing power station, so renovating the building is a priority. Even more pressing is making the structure safe. 鈥淎ccess was incredibly restricted when we first bought the site 鈥� almost the whole thing was an exclusion zone,鈥� says Rebecca Beveridge, Treasury Holdings鈥� assistant development manager. Because of this, Treasury is spending 拢2m on making the building safe and preventing further crumbling while the new proposals wait for planning permission. 鈥淚t鈥檚 a combination of stopping the deterioration of the building and opening it up to give us access,鈥� says Beveridge. 鈥淚t demonstrates our commitment by putting our money where our mouth is,鈥� she adds, obviously mindful of the history of lack of action by previous Battersea developers.

So what does Treasury Holdings need to do to restore the building to its former glory?

The power station has barely been touched for 25 years. The first developer, John Broome, actually damaged the building by removing its roof, and the last developer, Parkview, made almost no impact. 鈥淧arkview attempted to clean a few drains and put up netting to keep the pigeons out, but that was as far as it went,鈥� says Jim Solomon, Buro Happold鈥檚 conservation engineer on the scheme. He adds that Treasury Holdings is 鈥渄oing a far more comprehensive job鈥�.

The mortar is one of the hardest mixes I have ever come across, a specific type of sharp sand and white cement. You can鈥檛 salvage anything from it

Bob Davies, Szerelmey

Solomon says there are two key areas that need tackling to bring the building back to a useable state. The first is the fabric of the chimneys. Solomon says there are significant levels of chlorides in the concrete. 鈥淲e suspect they used river water to mix the concrete, which is of course saline,鈥� he says. There are also high levels of carbonation 鈥� both these problems lead to corrosion of the steel reinforcement, which causes spalling and cracking.

One solution to the problem is cathodic protection. This is an electrochemical process in which another metal corrodes sacrificially rather than the original steel. However, for this to work, an electrical current needs to pass through the concrete and cracks in the chimneys prevent this. Solomon says the chimneys could be patched up, but this would only last a few years. 鈥淵ou would end up replacing the chimneys before the project was finished, which doesn鈥檛 make any sense whatsoever,鈥� he says. In the long term, the chimneys simply can鈥檛 be saved.

The second big issue is the interface between the building鈥檚 steel frame and the brickwork. Battersea Power Station may be Europe鈥檚 largest brick building, but those massive walls are only 225mm thick and are supported by a steel frame which in many places is embedded in the brickwork. 鈥淭he steelwork is corroding as it鈥檚 encapsulated in the brickwork, which has got very wet over the years. The brickwork is cracking because the steel is expanding and forcing the brickwork apart,鈥� says Solomon.

Dealing with all this is going to cost about 拢150m. One of the first jobs will be to demolish the chimneys and rebuild these exactly as the originals, using insitu concrete. This means the 30m exclusion zone can be removed. The chimneys do not go down to the ground, but are supported by a steel frame that will also need strengthening. This area was known as the wash tower, a feature of the old power station, where water was sprinkled on the coal smoke to wash out the sulphur. Unfortunately, this creates a dilute sulphuric acid, which has corroded the steel. Rather than replacing the steel, a 300mm thick concrete liner will be built to take the weight of the chimneys.

According to Solomon, the chimney replacement and wash tower strengthening work will probably hoover up half the 拢150m budget. Much of the remaining money will be spent on the brickwork and steelwork. The lack of the main boiler house roof and leaks in the roofs elsewhere have caused the steel frame to rust, particularly the parapet support beams. These will need replacing and the brickwork will have to be repaired. The building has cracked near its corners because of the lack of movement joints; again, this will need repairing. Cathodic protection will be used to prevent any further damage to the steel frame.

The peregrines are a schedule one bird and we will have to accommodate them. It鈥檚 a merry dance.

Rebecca Beveridge, Treasury Holdings

Locally based contractor and restoration specialist Szerelmey has already started work on stopping the structure deteriorating any further. Central to this is stopping any more water from getting into the building. The first job was to fix the guttering. 鈥淭he rainwater pipes were broken and smashed up but now they are repaired and clean so water goes through them to the ground rather than through the building,鈥� explains Bob Davies, Szerelmey鈥檚 contracts manager for the job.

Szerelmey has carried out temporary repairs to the flat roofs on either side of the boiler house, which involved patching up the existing roofs and in some cases re-covering them with asphalt. It has also taken out the glass from the rooflights and removed asbestos sheeting. To make them watertight, the rooflights have been covered with a plastic sheeting called EnviroWrap. When the building is restored, the roofs will be renewed.

The brickwork is being repaired where it is still dangerous, which involves replacing it in some places and stitching it together in others. Again, much of this will have to be redone; for example, the parapet beams will have to be taken out and the parapet rebuilt later on. 鈥淲e are limited in what we can do as we are working off cradles. Also, some of the steel has to come out so there鈥檚 no point in doing permanent repairs,鈥� says Davies. New bricks have been specially made for the repairs as the originals can鈥檛 be salvaged because the mortar is so strong. Davies says: 鈥淚t is one of the hardest mixes I have ever come across, a specific type of sharp sand and white cement. You can鈥檛 salvage anything from it.鈥� The river wall also needs attention where barges have damaged the brickwork; this work is further complicated by having to be done at low tide.

In its years of disuse, the empty site has attracted a lot of wildlife, including a pair of peregrine falcons, which has delayed the job for two months. 鈥淲ork had to be suspended and the area sealed off because peregrine falcons were attempting to nest at the top of the boiler hall wall,鈥� says Davies. Work finally started again three weeks ago as the peregrines didn鈥檛 successfully breed. Treasury Holdings has put up a temporary tower near the river in an attempt to persuade the peregrines to nest there instead, as otherwise they could cause more delays to the project. 鈥淭hey are a schedule one bird and we will have to accommodate them,鈥� says Beveridge. 鈥淚t鈥檚 a merry dance.鈥� She could be describing the past 25 years. The real test for Treasury Holdings now is getting planning permission for the scheme, raising money and consigning the dismal view from the base of the derelict chimney to history. That鈥檚 really quite a challenge.