Remixed and remastered, the lime is now
At an 18th century folly in Berkshire, Ian Pritchett has demolished the walls of lime鈥檚 conservationist ghetto by repackaging the material in the most modern of forms. In delivering premixed lime mortar and plaster to site in a silo for the folly, the MD of IJP 星空传媒 Conservation believes he has made the material suitable for modern construction methods. He鈥檚 even set up a company, Lime Technology, on the strength of that conviction. During the last 100 years, cement mortars and renders have ousted lime as the standard for glueing masonry and protecting it from rain. On big housing projects, cement mortar silos are a common sight, allowing contractors to rid themselves of the mess, expense and inconsistency of a labourer operating a cement mixer. By contrast, lime technology has retained a craft mystique 鈥� and remained a niche material in the process. Concrete cock-up
The job that gave birth to the silo idea was a temple to the goddess Diana in the grounds of Highclere Castle. The top half of the Grade I listed folly 鈥� a dome supported by a drum 鈥� was in a disastrous state. A cement render put on 80-odd years before hadn鈥檛 so much protected the brick-built dome and drum as hastened its disintegration. Nearly all the render had slid off and lay in rubble on the gallery that runs around the base of the drum鈥檚 vertical walls. Even worse, a great many of the bricks beneath had disintegrated, broken up by rain and moisture entering through cracks in the render and, unable to escape back out through the impermeable cement, subsequently freezing in winter. Stripping off what was left of the cement and replacing damaged bricks with new ones handmade by local brickmaker HG Matthews was easy enough. The big challenge lay in covering the renovated structure with a render containing 850g of magnesium sterate 鈥� highly water-repellent, synthetic pig fat, incorporated to ensure no standing water could accumulate on the flat top of the dome 鈥� per tonne of lime. The perfect blend
Getting the quantity exactly right is crucial to lime鈥檚 ability to let vapour pass through, but as magnesium sterate comes in 125g bags, mixing it on site would mean measuring it out on a pair of scales. Instead, Pritchett decided to have the mix factory-blended and delivered to site in a 7m-tall silo. The refillable silo can hold 22m3 of dry lime (the folly used 25m3) and automatically regulates the amount of water mixed in. The silo gives a consistently accurate mix, and leaves no packaging or waste to dispose of. The scaffold is now down and the folly, says Pritchett, looks spectacular. 鈥淐ement has ruled for the last 50 years,鈥� he says, 鈥渂ut it鈥檚 too hard and rigid for good mortars and plasters. Cement鈥檚 forte is cast concrete and high-strength engineering. Lime has hitherto been available only through cottage industries. Now it comes in a form new-build is used to using.鈥� Why lime鈥檚 no lemon
Crusading for medieval tradition
In his long-running restoration of Ightham Mote in Kent, architect Stan Goodman has worshipped at the shrine of tradition, vowing whenever possible not to besmirch the medieval manor house with modern materials. Beneath the surface, though, one of the most contemporary of materials, the vapour-permeable membrane, underlies the building鈥檚 clay-tiled, oak-trussed roof and lime-rendered, chestnut-lathed, oak-framed walls. This summer Goodman started on the final phase of the 15-year-long project. Deathwatch beetle, neglect and an earlier cement render had damaged much of the wood holding up the roof and external walls. Goodman took the roof apart, repairing every one of the salvageable roof timbers, before putting it all back together in the same position as before. The National Trust wants to preserve the original design and materials of Ightham Mote. So why introduce something so manifestly alien to the Middle Ages as a vapour permeable membrane from Klober? 鈥淭o restore weathering to the building,鈥� explains Goodman. 鈥淚ghtham Mote suffers from high winds, and fine snow gets blown into the roofspaces.鈥� Draped on top of the roof鈥檚 14th century oak timbers, a Klober Permo Forte membrane keeps out the rain and snow, and prevents condensation and mould. Any water that penetrates the hand-made clay roof tiles and their sarking felt sits on the surface of the membrane and evaporates in the draught from the eaves. Between the external and internal walls, sandwiched between two sheets of Permo Easy membrane, Goodman put Second Nature鈥檚 Thermafleece wool insulation, which also allows vapour to escape. The membrane protects the Thermafleece from air, wind and rain 鈥� as well as the lime plaster when it is being applied. Despite being high-tech, vapour-permeable membranes are also a throwback to 14th century building materials, all of which allowed structures to breathe. As far as Ightham Mote is concerned, Goodman is still keeping the faith. Easy as ABCM
The CIOB recently launched the Association of 星空传媒 Conservation Management to help members manage works on historic buildings. This aims to promote best practice, accredit building conservation companies and courses, and publish papers and seminars. For more information, contact Sue Dennison on 01344 630730. Between the sheets
Vapour-permeable membranes made of non-woven polypropylene offer the same sort of protection to buildings as Gore-Tex. Because vapour can pass through the material, it doesn鈥檛 build up as condensation when it cools. The membrane is nailed or stapled to rafters and beams and comes in rolls of 50m by 1.5m. While the 拢115 materials cost of a 75m2 roll of Permo Forte compares poorly with the 拢10 cost of a 15m2 roll of bituminous felt, it requires no extra outlay on ventilation products in the roof cladding. Membranes are currently installed in 20% of new UK roofs. Enquiry numbers: 201 (Klober); 202 (Second Nature)
TV man gets wall-to-wall coverage
WHEN HE first BOUGHT the Lymm Water Tower, a 130-year-old octagonal sandstone building in 1997, TV presenter Russell Harris simply planned to build in the grounds. But after several false-starts, he decided to convert the 25m tower, which looms high above the Cheshire plain, into his own private residence instead. Plasterboard has been the key material in the conversion. 鈥淭he tower wasn鈥檛 built as a perfectly accurate construction,鈥� says Andrew Thompson of Ellis Willams Architects. 鈥淚t was just a water tower and the walls were all over the place.鈥� Built of sandstone blocks in 1870, the walls thin out as they rise to the top of the tower. The blocks had shifted during the years and were roughly finished. Smoothing out the imperfections with blockwork and plaster would have added too much weight, so Thompson put up timber-framed plasterboard from British Gypsum. In the tower, Thompson has used the cost-effective, flexible material to create circular rooms, octagonal rooms and even a conical entrance hall. Enquiry number 203
Can-do cradle does the job
When your client suddenly demands you shorten the eight weeks remaining on a 24-week escalator replacement job to four, you could be forgiven for telling them, in the nicest possible way, to get stuffed. But when that job is one element in an 18-month, 拢30m contract that represents half your annual turnover for a long-time customer, you鈥檇 be wise to hold your tongue. 鈥淚t was all because of Megaday,鈥� groans John Williams, operations director at fit-out company Support Services Group, which started refurbishing House of Fraser鈥檚 Rackhams department store in the centre of Birmingham in 2002. On Megaday, Rackhams puts all goods on special offer for that day only, keeping the Megaday date secret for as long as possible. Open all hours
It also pulled the rug out from under Williams鈥� programme. Rackhams, a huge store, the third biggest in the UK in terms of floor space, continued trading while Williams was doing the refurb, and wanted the 14 new escalators fully functioning on one of its biggest trading days of the year. Although the new escalators were already in by that stage, they were far from complete, lacking handrails and sides, and were uncommissioned and untested. Even worse, there was scaffolding running up and down them, which was needed to build the ceiling details: there was a big hole where the concrete floors around the escalators had been cut back to create a bigger, lighter atrium. To get back on track with the truncated programme, Williams replaced the scaffolding with a cradle that ran through the 1.5m gap in the floors. 鈥淭hat let us go a lot quicker,鈥� says Williams. 鈥淲e finished by Megaday, although it wasn鈥檛 till the morning before that we tested the escalators by getting the entire shop staff to go up and down them a couple of times.鈥� Size matters
As well as the unilateral programme pruning at the end of the escalator phase, Williams had a nasty surprise at the beginning. The only way to take out the old escalators and bring in the new models was through the front entrance. But when they removed the timber cladding from the canopy above it, they found the concrete beam holding it in place dropped lower over the entrance 鈥� so low that they couldn鈥檛 get the new ones in. 鈥淚t was a moment of horror when we realised,鈥� says Williams. 鈥淚t knocked our plans for six.鈥� As the concrete had a structural function, he had to leave it in place. In the end, manufacturer Otis had to take off the handrails and glass sides at the factory and fit them back on in situ. Rackhams restored
The retail pride of Brum, Rackhams opened in 1957. At the heart of the refurb was the replacement of the original escalators with 10m-long glass/steel designs. The old escalators were removed in ascending order, and the new ones installed in descending order. Getting the old escalators out involved cutting through the horizontal stretches at either end with an oxyacetylene torch, attaching them to A-frames and winching them out through the front entrance. Outside the store, a crane lifted them onto a low-loader. Support Services did all the escalator work at night so that the store could continue trading during the day without construction noise. Enquiry number 204
Getting the better of Bedford鈥檚 black mould
Problem: Poor insulation and cold bridging. Solution: External insulation and renderAt Beauchamp Court in the centre of Bedford, things had got pretty grim. Some of the flats in the five-storey block had walls entirely covered in black mould. Built of brick-slipped concrete in the 1950s, the block was paying the price for extensive cold bridging from exposed concrete ring beams as well as poor insulation from a wall cavity only 10mm wide. Given the block鈥檚 prime location in the centre of Bedford, Patrick Lyall of Bedfordshire Pilgrims Housing Association, the inheritor of Bedford鈥檚 council housing stock, didn鈥檛 want just to pebbledash it. He decided to install Alumasc鈥檚 MR Swisslab external wall insulation 鈥� a solution already successfully used on a solid-wall estate in the town. This involved cladding the block with polystyrene insulation board, putting a mesh-reinforced render on top, and finally applying a high-performance coat of through-coloured render. Living conditions
It has brightened up what was a dark and dingy block (each time it rains, the dirt washes off, so clinker doesn鈥檛 build up as it used to), shielded the building鈥檚 flanks with insulation, and removed cold bridging by covering up the exposed ring beams. The refurb also glassed in the open balconies, which had led to regular flooding when the internally routed pipes draining the balconies overflowed. The flats no longer flood and the black mould鈥檚 all gone, so is Lyall happy? Yes and no. While conditions are far better, no construction solution can ever solve a condensation problem on its own. 鈥淪ocial housing goes with fuel poverty, and if people don鈥檛 heat their flats, there will still be problems.鈥� Enquiry number 205
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Construction Manager
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