How to build a small vertical shaft lime kiln
Practical Action
Construction details
The construction details, shown on the drawing, are largely as for the Chegutu kiln with
some improvements. In addition the following should be noted:
There should be no connection between the inner and outer brick skins above the draw
box. This means the concrete platform at the top must be supported on the outer brick
skin only and not touch the inner shaft. The steel chimney must be supported on the
inner brick skin only. The chimney base plate extends over the edge of the concrete
platform slab to prevent water from running into the gap between the two brick skins.
Also, the vermiculite concrete infill must be cast with a paper joint between the
surface of the inner brick shaft and the infill to allow the shaft to move separately from
the outer casing.
A brick course is assumed to be 90mm in height and a brick 230mm long, including
mortar joints.
The circular shaft is constructed in refractory bricks above the kiln floor. The bricks are
laid as headers with overlapping vertical joints. They must be laid very tightly together
on the internal face (see section B-B). Any mortar spilling from the joints should be
cleaned
off to give a smooth internal face.
Refractory bricks have been chosen for the circular shaft to reduce the risk of
abrasive and heat damage. These bricks are very expensive at approximately
12 times the cost of common bricks. An alternative may be to use refractory
bricks only between courses 23 and 42. In this case, the lining may need to be
replaced more often.
Tension bands should be tightened gently, avoiding damage to the brick corners.
Reinforcing bars are required for the concrete floor of the kiln, the draw box and the
platform. The reinforcing required is shown on the drawing and listed in the bending
schedule.
The concrete should be cured well, keeping it wet for at least seven days. The slab can
be covered with a layer of sand to help retain the moisture.
Vermiculite concrete infill between the two brick skins should be cast in layers of no
more than 1 metre in height.
Inspection holes are also used for poking the lime during production and it is important
that they are firmly fixed. Flanges have therefore been fitted to each end of the tubes.
Bending schedule
Bar mark
01
02
03
size
10mm square twist
No of
8
10mm square twist
10mm square twist
10
4
04 10mm square twist 4
05 10mm square twist 6
06 10mm square twist
07 10mm square twist
Cover to reinforcement: 40mm
4
4
Dimensions
725
70
100
100
725
725
725
500
100
2065
500
75
2065
1000
100
100
500
100
500
75
1000
3