A small kiln for batch & continuous firing
• Insulation skin
Hand-made insulation bricks in mud mortar, 2:1 (dambo sand: river sand).
External pointing and mortar for top five brick courses is 3:1 (river sand: hydrated lime)
The chimney is a 200 litre oil drum. The chimney is removable for loading the kiln. It has an
angle-iron frame which rests on the capping slab. Draught could be increased by extending
the chimney with a second drum. Alternatively a chimney could be fabricated from mild steel
sheet or built in brick. If chimney height is increased, then more secure fixing will be required
and a loading door will be needed in order to charge the kiln.
• Kiln height
The height of the kiln is similar to the gable of a single-storey house: a height builders will be
comfortable working with. Being under 4 metres high means that no special foundations are
needed on soil with good load-bearing characteristics.
Limestone burned at Dedza breaks up into powder as it changes to quicklime. Hence,
unloading is achieved by raking quicklime via the output port and removing it from the
fireboxes. Where quicklime remains in virtually stone size pieces, a larger output port with a
steel door should be considered.
• Fire brick spacing
The spaces between fire bricks in the top of the fireboxes (which is also the firing chamber
floor. See detail on elevation A–B, page 6) are determined by stone size and type and should
be adjusted as experience is gained. At Dedza, using stone with a diameter of 45 to 60 mm
which burns to a powder, the spaces are set at about 80 mm.
Construction details, given in the following drawings, are for the experimental Dedza kiln
incorporating minor improvements.
With a firm and rocky subsoil, as would be expected in lime producing areas, a foundation
between 60 and 80 centimetres deep will be adequate. The foundation platform should cover
the full square area of kiln and buttresses.