CONSTRUCTION PROCESS OF A FUEL EFFICIENT KILN

CONSTRUCTION PROCESS OF A FUEL EFFICIENT KILN

1 EDITOR Conor Fox CONTIBUTORS Elizabeth Nyirenda Cristel Chong Christa Roth Hellen Owala DESIGN AND LAYOUT Marcelo Lima Charles Banda ILLUSTRATIONS Hendie Mawera CLIOMA LTD PRIVATE BAG 78 LILONGWE INFO@CLIOMA.ORG June 2012 All rights reserved; no part of this publication may be produced, stored in a retrieval system, transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or other wise, without prior written permission of the publishers.

ACKNOWLEDGEMENTS 2

3 BUILDING KILN CONTENTS Foreword 4 Background 5 Types of kilns 6 Materials for building kiln 8 Tools for construction 10 Steps in building a kiln 10 Building the kiln 15 The kiln wall 19 Preparing for firing 21 Indicators of complete firing 27 Repair and maintenance 27

FOREWORD 4

5 BACKGROUND Long before kilns were known, people used to fire pottery on open bon fires. This method proved less efficient as items were half baked. In bad weather such as windy and rain a lot of fuel wood was wasted but pots could not get fired properly. Later a shallow pit or small wall was used to enclose fire but most cracked due to quick cooling and uneven heating.

6 With time people started to fire items in built structures called kilns. Nowadays, technology has led to improved and effective kilns that are environmentally friendly like a Better Bon Fire. TYPES OF KILNS: There are different types depending on the individual production needs. 6 Large kiln - 110 cm Medium kiln 85cm Individual kiln - 75cm

7 Site for construction: It should be constructed on a higher ground to keep away moisture during the wet season. Should be away from houses and flammable items as smoke and flames come out during firing. Should have enough space for storing fuel wood and pottery. A good site for Kiln

8 MATERIALS FOR BUILDING KILN Large Kiln MATERIAL QUANTITY SPECIFICATIONS Fired bricks 400 pcs Large 91/2 x 5 x 41/2 100 pcs Small 81/2 x 4 x 31/2 Heavy duty Plastic sheet 7 metres Heavy duty 2m width Stones 10 wheelbarrows Hard stones that do not absorb water Gravel 10 wheelbarrows Medium course Water for building 500 Litres This is equal to 4 drums of water Binding wire 2Kg Chicken wire 8m Reinforced rod 12m 1/2 diameter twisted bar Tire wire 2Kg Medium kiln: MATERIAL QUANTITY SPECIFICATIONS Fired bricks 100 pcs Large 91/2 x 5 x 41/2 100 pcs Small 81/2 x 4 x 31/2 Heavy duty Plastic sheet 2 metres Heavy duty 2m width Stones 6 wheelbarrows Hard stones that do not absorb water Gravel 10 wheelbarrows Medium course Water for building 300 Litres 300 Litres Small or individual Kiln MATERIAL QUANTITY SPESIFICATIONS Fired bricks 70 pcs Large 9.5 5 x4.5 40 pcs Small 8.5 x 4 3.5 Heavy duty plastic sheet 2m Heavy duty 1.5m Stones 3 wheel barrows Hard stones that do not absorb water Sand 3 wheel barrows Gravel 4 wheel barrows Materials for building will vary according to material availability and choice.

9 Metal sheet or ceramic plates for supporting firebox top brickwork 6 pcs

10 TOOLS FOR CONSTRUCTION: A hoe, a spade, a wheelbarrow, a pick, tape measure, builders line, spirit level, mason s hammer. STEPS IN BUILDING A KILN As there are varying types of kiln sizes I will explain the large type as all construction details remain almost the same except the measurements.

11 The kiln foundation Level the ground of the site. Erect a pole and tie a sharpened stick to a rope about 110cm from the central pole. Make a circle of diameter 220cm with the sharp stick.

12 Dig a pit covering the circle area, diameter 220cm and 50cm deep. Cover the bottom of pit with a layer of sand at least 5 cm thick.

13 Lay plastic sheet over the sand to cover the base and overlap at the sides of pit 10cm. Put another thick layer of sand over the plastic to protect it from sharp stones. Put a layer of small stones, gravel or broken pottery and flatten it with a rammer or piece of wood.

14 The foundation should be just above the ground and should be leveled.

15 Measure 75cm from the centre pole and make a circle to make the inner diameter of big kiln. BUILDING THE KILN Do not use cement as it will crack in heat later during firing.

16 Fired bricks should be used and the first circle should be laid as shown: Level each brick as it is laid until a full circle is complete. Trim off the plastic sheet overlapping the circle of bricks.

17 Make 6 firebox walls each 18cm wide with the same size bricks as the circle. The bricks at the end of each row should be shaped to fit within the outer circle of bricks. Fill the spaces between the firebox walls with mud or gravel and level it using a rammer:

18 Lay the second course of firebox wall bricks leaving a 10cm ventilation space between each brick. There should be three ventilation gaps in each of the two outer channel walls. The complete fireboxes. The firebox channels are where the pottery items sit during firing. Note : firebox channels for medium and individual kiln is three. At this stage fit a metal ring to reinforce the kiln wall that will be added above fireboxes The size of bricks and kiln diameter determines the size of metal ring.

19 Fired clay bars, specially made large bricks, can also be used to support the kiln wall above fireboxes. THE KILN WALL The wall starts above the firebox doors and goes to a height of 1metre The wall is plastered with mud.

20 The dome is made of dry grass which is put on top of pottery and covered with mud. The dome also acts as heat distribution control area to parts of the kiln if heat is uneven. The dome of kiln is added later after pottery is loaded to keep the heat and may vary in height depending on the kiln load.

21 Now the kiln is finished,wait for a few days for it to dry before test firing. PREPARING FOR FIRING Load of stoves on top of fire channels lines ensuring that stove holes are not aligned to allow flames to reach the top of kiln.

22 When the kiln is full, stack stoves in a curve shape to form a dome later. Open spaces should be filled with broken liners to form a smooth dome.

23 Cover the top of kiln with grass and then mud 2cm thick to make a dome. Firing is done by priming the kiln for 2-3 hours and then maintain a steady firing temperature for 6 hours. In windy weather,light the fireboxes from the direction of wind. Leave the other fireboxes unlit to act as chimneys. After 2 hours light the unlit fire boxes. Feel the outside of dome to detect cool areas in the kiln, make a hole on that side on the dome to draw heat to the area and fill it if the heat is reached. Repair the cracks that appear on the mud dome with mud.

24 Evenly spaced cracks show even distribution of heat in the kiln. Ensure fire is evenly distributed along the fireboxes by poking the charcoal along it.

25 Close fireboxes in the direction of strong wind and open if firewood is to be loaded and close again.

26 Close all doors once all parts of kiln are fired and leave the kiln to fire further. Note: unfired pottery contain e 100 degrees celcious so if firing is fast, pots crack. At 580 degrees celcious the quartz in clay expands so if firing is fast, it cracks. By the following morning the kiln is cooling so open the doors and then dome slowly at intervals to avoid quick cooling which may break the stoves.

27 INDICATORS OF COMPLETE FIRING! The grass between liners and dome become fired and looks white in color.! Unburnt grass may produce smoke that may go down in kiln and make pottery black and so contribute to poor quality! Red glowing stoves can be seen through the holes on the dome. REPAIR AND MAINTENANCE After every firing, inspect the kiln for cracks, sinking bricks, loose or falling bricks and repair immediately.

28 Firing kiln consume alot of fuel wood. Prepare for future projects by planting your own trees to prevent deforestation.