A stitch in time

Metalocking has been around for over 75 years and is a tried and tested system for repairing cracks in cast metals by literally stitching them up.

working on Stretton Aqueduct, 1954 Waterways Archives working on Stretton Aqueduct, 1954

The metal stitching system involves using special tools to drill lines of holes at intervals across a crack and then tapping made-to-fit metal keys into the holes. Holes are also drilled along the line of the crack and filled with a series of metal studs that bite into each other to form a pressure-tight repair. The keys and studs that form the stitching are ground smooth before finally being painted.

Nantwich Aqueduct, metal stitch, 2015 (Mark Evans)There are many advantages to metal stitching; it is a well-recognised system that works as well for ships’ engines as for historic buildings, it is a cold repair that avoids the difficulties and distortions of hot welding and above all else it can be done in-situ. This is very important to our engineering heritage structures and over the years numerous cast iron aqueducts and bridges have been successfully stitch repaired around our waterways.

Two good examples are Thomas Telford’s fine aqueducts at Stretton and Nantwich on the Shropshire Union Canal. There are photographs in the Waterways Archive from 1954 that show Stretton Aqueduct undergoing metal stitch repairs. These have performed well over time and now, 61 years later, Nantwich Aqueduct has been repaired in the same way; a classic example of a proven repair method that has itself almost become part of our heritage.

Metal stitch repair, Stretton Aqueduct, 1954 Waterways Archives


Last date edited: 26 January 2016

About this blog

Nigel Crowe

As national heritage manager, Nigel’s role is to lead the Canal & River Trust’s team of regional heritage advisers in England and Wales. He has over 25 years’ experience of working in the conservation, archaeology and interpretation of historic buildings and places. He is a member of the editorial board of the Institute of Historic Building Conservation. He has written numerous articles concerning heritage conservation and is the author of several longer published works, including the English Heritage Book of Canals.

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