Context 139 - May 2015

24 C O N T E X T 1 3 9 : M A Y 2 0 1 5 MARK WATSON Iron frames in textile mills Historic textile mills, now redundant, introduced the metal skeleton frame to world architecture. Their new uses can be facilitated by subtraction as well as addition. The iron frame of the mill is the precursor to the steel frame of the skyscraper. In the industrial revolution the need for fireproof systems was recognised after several costly fires in early timber-floored mills. Iron frames could provide the support required for solid floors. Some of these pioneering structures were almost immediately demolished. One of the most important, Ditherington Flax Mill, Shrewsbury, survives and is now in the care of Historic England. Built in 1797, it has the first iron beams, and as both its floors and walls are brick, the shell of the building is incombustible.The power system that brought rotative power to the spinning frames was threaded through the ironwork, vertically through small holes cast into the beams and soon afterwards horizontally on two floors. Spans of 20 feet or more require intermediate supports. Square timber posts continued to be used in warehouse construction for much of the 19th century, with timber pads wedged above and below the posts to spread loads and avoid crushing. Cast-iron columns offered much greater compressive strength and slenderness.The oldest industrial building yet found to contain them in a regular layout is Bell Mill at Stanley Mills, Perthshire, of 1786, conserved and presented by Historic Scotland. Its cruciform columns transfer load through each wooden beam.The primary concern was to transmit mechanical power. Structural needs were secondary. Next was the development of interconnecting columns which transferred loads through floors. Columns could spigot through beams where they met or the ‘saddle’ transferred load down either side of the beam to the next column. This seems first to have been adopted in textile mills, and is almost universal in mid- to late-19th century floor maltings. Timber beams could be tensioned by wrought-iron rods running either side of the beam to meet at cast-iron stirrups. This – the composite or trussed beam – is apparent on a building exterior as a regular series of cast-iron tie plates, often wrongly seen by surveyors as evidence of attempts to remedy building defects. Timber continued to be the most common flooring in industrial buildings throughout the 19th century, fire-resistance perhaps being enhanced by lath and plaster or by fitting beads to joins between ceiling boards. Alternatively laminated timbers produced floorboards 2-4 inches thick that would char rather than burn: the ‘slow-burning’ floor favoured by American insurers that enforced a virtual exclusion of structural iron from US textile mills.This heightens the peculiar importance in early iron-framed construction of British textile mills, and particularly flax spinning mills. Two rows of cast-iron columns were not an optimum layout for the spinning mule used in the cotton and woollen sectors, so the majority of English and Scottish early 19th-century cotton mills had timber floors. Of all the Scottish woollen mills in the four main tweed and tartan producing counties, only one wing is fireproof – EttrickMill, Selkirk, 1850,with floor arches of whinstone, not brick.The number in the English woollen industry (Huddersfield and Stroud areas) is also low compared to the higher proportion of worsted mills (in Bradford, Keighley, Halifax) that are fireproof. The ideal beam formwas debated after some dramatic failures, including cumulative collapses in Oldham and Salford. The parabolic hog-back was introduced to overcome the stresses in the centre. Usually its bulge will be hidden within the depth of the floor but there will often be locations where part of the floor has been removed and the cross-section may be examined. If carrying a water tank, or flat flagstone floors, the hog-back is inverted, becoming instead a ‘fish belly’. The oldest beams had an inverted T-section, and a very narrow bottom flange. A cambered underside was adopted in the design-and-build package supplied by Fenton, Murray and Wood of Leeds to Broadford Works, Aberdeen, in 1808, and seen in their mills in Leeds, Shrewsbury,Whitehaven andWhitby. Iron-framed buildings of the 1820s and 1830s favoured a flat-bottom flange of around six inches, the better to serve as spring- ing points for brick arches. Experiments in Manchester Kilncraigs Business Centre, Alloa, contains several of functions of Clackmannanshire Council. Built as a yarn store for Paton’s, spinners of hand knitting yarns, its several phases are revealed in the different column types shown by the section cut through the building, reducing its great depth and allowing a full-height lobby and circulation area. (Photo: David Henrie ©Crown Copyright Historic Scotland)