ST. PAUL’S CATHEDRAL

Wairarapa Times-Age, 25 October 1939, Page 3

ST. PAUL’S CATHEDRAL

SIR CHRISTOPHER WREN’S ERROR “There is reason to think,” says Mr A. T. Bolton, editor of the final volume of the Wren Society on St Paul’s Cathedral, “that by 1680 Sir Christopher Wren had realised that a capital mistake had been made in the use of a rubble core inside a shell-like casing of Portland stone, in view of the great direct load upon the piers of the dome.” The total weight of the dome has been estimated at 44,620 tons. When Wren started the work in 1675 he had only had 12 years’ experience. Mr Bolton suggests that he may have been unduly influenced by the old-fashioned ideas of the master masons, Joshua Marshall and Thomas Strong, who had been trained according to mediaeval traditions. They, were more familiar with the elastic transmitted thrusts of the old cathedrals and inclined to underestimate the effect of imposing such a huge weight as the great dome. If Wren had understood and adopted the Roman method of using brick and plaster for interiors, the stone used to line the interior of St Paul’s would have gone far to make his great piers solid.

At the floor level the piers rest on the rubble filling of the greater piers of the crypt. This, says Mr Bolton, “showed a sublime confidence in'the quality of the mortar used to bind together the miscellaneous rubble within the relatively thin stone casing.” Trouble arose during the later stages of the work and Wren undertook the delicate and dangerous process of drawing the facing in the worst places in the crypt, where bursting pressure was most evident, and replacing it by new masonry. Only master masons were engaged for this anxious task. Between December, 1709, and June, 1711, £7.421 —equal to four or fife times as much money today was spent on repairing flaws occasioned by pressure, opening joints and actual splitting and crushing. The fact that the piers stood for more than two centuries before the recent work on them became necessary speaks well for the strengthening methods used by Wren. The weakness of the rubble cores caused Wren to modify his design by reducing the external diameter of his great dome, so that the circle strikes the centre line of the supporting arches instead of the external edge. The effect of this is that from a distance the dome appears slightly inadequate.