The other day I was told “You wouldn’t want to build a wall
out of lime mortar; it’s only good for pointing.” I found this an incredible
statement and it made me think of the structures that most excite me all built
with lime mortar.
Industrial chimneys!
- Now just bare with me as I explain where I’m going with this!
What on earth do industrial chimneys have to do with the
abilities of a Lime mortar? The answer is everything.
Today we think of a tall steel streamlined flues poking out
of the side of industrial steel sheds. But from the beginning of the industrial
revolution until the mid 20th Century the great majority of these
magnificent chimneys were made from bricks and mortar... lime mortar. I’m not
talking about the small chimney to the blacksmiths forge or to the cottage down
the road, I’m talking about the kind of structures which were erected to serve
pumping stations and other sites which had any sort of boiler or engine,
utilities, light and heavy industry, all these required a tall flue to vent the
gases from these sites.
The usual thought when talking about
these is to think about the countries industrial centres such as Bolton in the
early 20th Century (above) when its sky-scape would have looked a lot
different to today, but these amazing structures where all over the country,
pumping water, fresh or waste, and doing many other things.
These structures came in numerous shapes and sizes, square,
round, octagonal etc, the one thing which they all shared was that they were
built by incredible craftsmen, who were not only able to lay the bricks even
and true, but were able to shape these with the right batter and consistent gradual
slope to heights of over 300-400 feet, in situations where the courage and experience
of the craftsman must have been enormous. Looking back these activities and the
lack of health and safety makes me go cold! But they were very different times
when mindsets were very different.
One of the largest examples of these structures was the
chimney at St Rollox Glasgow, built for Messer’s. Charles Tennant & Co
Chemical works:
·
The total height from bottom of foundation to
top of coping was 455 ½ feet (138m).
·
Ground level to the top of coping it was an
impressive 435 ½ feet (132m).
·
The outside diameter at foundation level was 50
feet (15m), at ground level the outer diameter was 40 feet (12m), with a
diameter at the top of 13 ½ feet (4m).
·
The height from ground level was divided into
five sections.
·
The thickness of wall varied from 2 feet 7 ½
inches at the bottom of the shaft, to 1 foot 2 inches at the top.
·
Foundations, no piles were used, instead the
inner (an inner masonry cone was built to
offer some protection to the outer masonry from the intense heat of the flue,
but this was shown to not have desired results) and outer structures were
built on stone footings, this can be best explained by the drawings below.
Picture from, A practical treatise on the construction of
tall chimney shafts. Farncomb & Co Lewes East Sussex. 1885.
Picture from, A practical treatise on the construction of
tall chimney shafts. Farncomb & Co Lewes East Sussex. 1885.
Apart from the coping stones, the chimney was made entirely
of bricks:
·
1,250,000 bricks weighing 125lbs per cubic foot.
The bricks were of the finest quality and were fired from a mixture of ironstone
and blue clay. Many of the bricks used
in the construction of tall chimneys were Nori bricks, these are still made
today. (Accrington bricks, or Noris
are a type of iron-hard engineering brick, produced in Altham near Accrington,
Lancashire, England from 1887 to 2008 and again from 2015. They were famed for
their strength, and were used for the foundations of the Blackpool Tower and
the Empire State Building. )
·
Brick bond was described as ‘old English’.
·
The mortar was an Arden Lime, this was a
naturally occurring lime which was high in natural contaminants making it strong
(hydraulic), this enabled the lime to be sand slaked on site and used
immediately due to its good setting speed and strength.
As can be seen in this picture, when it was built, the
chimney was the 7th tallest structure in the world.
Where Arden Lime was not used a common mixture was:
·
Bricklayers mortar – 1 slaked lime, 1 Sand, 1/3 Smithy
ashes, this was the pozzolan to increase the strength of the mortar.
·
Masons mortar - 1 slaked lime, 2 Sand, 1/3
Smithy ashes, this was the pozzolan to increase the strength of the mortar.
(Anyone interested in understanding more about lime mortars
please see my other blogs about lime.)
Work started in June 1841 and the copings on the top were
laid in June 1842.
This equates to over 38 feet (11.5m) of chimney being built
every month!
I am aware that my passion for this could be a little romantic;
however the truth is that this and other structures were built to serve a
demanding purpose. In 1844 three iron hoops were required to the top of the
chimney due to a crack which had formed at the top, the intense heat, which had
been increased due to the inner masonry cone having the opposite effect of protecting
the outer masonry from the heat. In reports of the day it was noted that red hot
matter was seen coming out of the tall shaft. In 1871 lightening struck the
chimney, this did not destroy it, but it did lead to a total of 13 hoops being
placed around the chimney. In 1872 a lightning conductor was fitted.
In 1922 a bulge was found in the masonry, the chimney was first
reduced in height down to 90m, during this there was an unexpected fall,
killing 4 men and injuring 4. After this the remaining structure was felled by
dynamite.
Photo from The Herald
Scotland in 1922, showing the man on the plunger to destroy the remaining
chimney.
During the 20th Century The progression of boiler technology and the
modernisation of factories made the tall chimneys redundant, this was the fate
of most, apart from those which were lucky enough to be preserved or found a continuing
use.
An interesting item which I have uncovered during the time
looking at this blog I have learned something about the steeplejacks who were
tasked with re-pointing and maintaining these structures. They did not use lime, nor did they use
cement, it would appear that they used something called ‘mastic’. This was made
in the following way (I would not recommend re-creating this as it sounds like
a very toxic material!):
·
Clean washed and dry river sand.
·
Plumbers whiting (what they would make putty out
off).
·
Red Lead (a by-product of lead production).
·
Litharge (lead monoxide another by-product of
lead production.).
This would all be mixed up into a red paste with boiled linseed
oil ready to be applied.
I hope the above shows that lime is not for just re-pointing,
it was used to create incredible structures in the past, the raw material has
not changed, it is the mindset and lost craftsmanship which has created the
idea that lime is somehow an inferior product, nothing could be further from
the truth.
Thanks for reading
James
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