The museum mill chimney is an eye-catching landmark and a magnificent example of the art of bricklaying, if you stand close to its base and look up you will see that accuracy of edge and face is of the utmost importance in producing a strong yet resilient chimney. Resilience is achieved by using lime mortar not portland cement between the bricks, as portland cement is very rigid and would crack, not flex in high winds – yes It does sway! I am sure that you have seen old barns and stone built cottages with doors and windows that are well out of upright. This demonstrates that the lime mortar has been resilient over the years allowing movement without causing the building to collapse, the doors and windows would have had vertical sides and horizontal sills when it was built.
All the dimensions of the chimney at Coldharbour Mill would have been carefully calculated to produce the correct amount of draught, matching the power requirement from the engine and thus the quantity of coal burnt in the boiler furnaces. The London Building Act of 1894 requires that factory chimneys shall have a taper from base to top of at least 2.5 inches in 10 feet on each side and the width of the base should be at least one tenth of the height of the chimney. You may have noticed that there are ventilation grilles around the base, this is because the lower one third of its height is double skinned with a firebrick inner lining which can expand freely within the outer brickwork as it is the hottest part
of the structure.
For many years before lighting the boiler fires we, the volunteers, used to get down through a removable hatch into the flue at the base of the chimney and build a bonfire, light it, then retreat to the open air rapidly. We would then hope that it would keep burning long enough to produce a warm column of gasses rising up inside the chimney producing sufficient draught to start drawing the fires. This procedure was not without its problems, especially when the fire went out prematurely. While salvaging various bits and pieces from Tonedale Mill I was pleased to spot a large electric fan in the fabric finishing room which was used to extract all the loose fibre from the inspection and finishing tables in that area. We promptly took it back to Uffculme and installed it in the boiler house – a much easier and safer option than bonfires in flues!
John Jasper. August 2010.
