C O N T E X T 9 9 : M A Y 2 0 0 7 the wall scaffold boards would be bolted to the face of the wall, and through the wall, to further restraining timbers on the internal face (pictured in the two photos above). The horizontal boards were placed at 700mm centres up the height of the wall. When the wall was securely held, the contractor made a series of holes beneath the lower plank, allowed the dust and filling behind to fall out. He then made good this hole using stone on stone, with very little mortar between. He used stainless steel ties drilled into the backing construction and made good with a hydraulic lime-based mortar. This process carried on beneath the bottom plank using an underpinning hit-and-miss approach. When this was completed he went in above this plank, took out the stones immediately behind it, and consolidated those before cutting out further holes between the two planks above.This system worked well, saving the wall, and making significant savings in cost. In another case, a church gable constructed in flint had collapsed over perhaps more than half the length of the wall. The solid structure behind suggested that the remaining facing flints, where hollow behind, could be taken off and the outer face rebuilt with the original flint materials, starting from the bottom and working up.This is a straightforward situation that is fairly easy to deal with. Where the outer face is bulging away from the inner face (in the round tower churches of East Anglia, for example), we simply cut out the flintwork locally, carefully, allowing the flint over the new opening to arch over the hole and rebuild this incorporating stainless steel wire formed into ties. This is bedded into raked-out mortar in the thickness of the main wall. These ties would be formed of 4mm diameter stainless steel, bent on site by the contractor to a butterfly shape. It has been suggested to me that resins could be used for bedding these into the mortar, but we have used these only in extreme circumstances. This is simply because we are not sure of the strength of the interface between the resin and the lime mortar of the original construction. In another case, the wall of a house constructed of two skins of flint rubble has delaminated over its whole height (pictured on p8 top). The photograph on p7 shows the extent of that delamination, leaving a skin externally anything between 100mm–150mm. A section of this, probably two metres in diameter, had simply fallen and the wall below that was bulging. The problem associated with this, following our banging test, indicated that the wall was unsound over its whole height, perhaps some six metres. There were clearly dangers in attempting to do anything to the wall. After initially being baffled as to how we could save the remainder of the face, we have investigated grouting the cavity from ground floor level to the point where the collapse had occurred, to form a good base for either taking down areas of the upper wall and rebuilding on an underpinning basis. Alternatively we could grout the wall, depending on the success of our work to the lower section. The method of grouting from the bottom up is to break out small areas of the wall at perhaps 600mm heights throughout the wall, checking all the time with further small holes to see where the grout has penetrated. Extreme care is necessary in this process as too much pressure from the grout could cause the wall to burst. The grout has to be breathable at the same rate as the wall, particularly the pointing. Otherwise, as has happened to the east wall at Lincoln Cathedral, the hard grout inserted becomes a water barrier and the wall will not perform as it has historically. This results in the need to replace the outer face at maybe 30-year intervals. The stone becomes saturated, the water freezes and the stone breaks down. Brian Morton MBE is a consultant to the Morton Partnership, the practice he formed in 1966. A solid wall with no bonding raised fears that the outer face would fall away. Scaffold board bolted through the wall makes it safe while repairs are carried out.
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