Knowledge Brief

What are the good practices for the construction of the outer wall and the wicket gates (Ghaati) of a Zigzag Kiln?

A Zigzag Kiln (a Natural Draught Zigzag Kiln [NDZK] or an Induced Draught Zigzag Kiln [IDZK]) consists of:

1. Chimney
2. Centrifugal fan (in an IDZK)
3. Flue gas ducts
4. Central island (Miyana)
5. Outer wall
6. Wicket gates (Ghaati).

The construction quality of these components has to be good for the efficient functioning of a kiln. In this Knowledge Brief, the good practices for the construction of the outer wall and wicket gates of a Zigzag Kiln (NDZK or IDZK) are discussed. The good practices for the construction of a masonry chimney of an NDZK or an IDZK, and the flue gas ducts and miyana are discussed in other Knowledge Briefs.

The outer wall and wicket gates are designed and constructed to minimise heat leakage, and also to minimise leakage of cold ambient air into the kiln.

What are the good practices for constructing the outer wall?

The good practices for constructing the outer wall are as given below.

1. At least 1-foot-deep foundation pit is dug for the construction of the outer wall.
2. The foundation pit floor is compacted and evenly leveled.
3. Mud mortar (Gara) is used to construct the walls. The mortar must be aged for at least 2–3 days prior to its usage. It should be in the form of a homogeneous paste (texture similar to toothpaste).
4. The outer wall is constructed as a two-layered wall with soil filled in the space between the outer and the inner wall layers. This design minimises the heat loss through the outer wall.
5. The inner and outer walls are constructed in step footing arrangement.
6. Soil filling between the inner and outer walls is done in layers, simultaneously with the construction of the inner and outer walls. Every layer of about 1 foot of soil should be compacted to minimise the possibility of vacant spaces being left between the walls.
7. The outer and inner walls are plastered with mud.
8. Expansion joints are made on the inner side of the outer wall to reduce the possibility of cracks developing in the walls due to thermal stress developed during firing of the kiln.
9. One expansion joint must be made between two consecutive wicket gates.

What are the good practices for constructing the wicket gates (ghaati)?

The good practices for constructing the wicket gates are as given below.

1. Wicket gates are made in the outer wall for transporting green/fired bricks in or out of the kiln.
2. Collars are constructed on both sides of a wicket gate.
3. To close the wicket gate temporarily during firing of the kiln, walls are made on both sides of the collar. Both the walls must be plastered with mud mortar and the vacant space between the two walls filled with soil. This is done to minimise the leakage of hot gases out of the kiln or infiltration of ambient air into the kiln, and to minimise heat losses.