Start by putting the pieces in the kiln - first the ones that are heavier at the bottom, later the lighter ones over the others. Cover them with fired ceramic pieces, it can be roof tiles or flooring tiles for example. One alternative can be to cover the top of the kiln with a metal roof panel.
The firing process consists of 3 steps:
1. Heating (2 hours)
Start placing the wood outside the kiln, wood that is dry and first use the thin pieces, which will help in starting and maintaining the combustion. Make a ball of newspaper and place it under the wood to start the fire. When the fire is already going on, you can start putting bigger pieces of wood - 1 or 2 pieces, beware to not stop the fire. The flame should be kept outside the chamber. After 1 hour, you can start pushing the wood inside the chamber, but not yet allow the flame inside. This fire must be kept outside the fire chamber for 2 hours.
2. Feed the fire chamber until incandescent (can vary in time, at least 2 hours)
After this period of time, you can start to introduce wood in the chamber, very slowly, to not cease the fire and to not impact with too much heat (the heat impact can break the ceramic pieces). Keep burning like this for 2 hours, feed wood according to the necessity, slowly.
If you hear a sound of burst coming out from the ceramic chamber, take the wood a bit out of the fire chamber and wait half an hour to start introducing wood there again. If you have just a few pieces, this step can take around 2 hours again, if the kiln has more pieces, more time might be needed until pieces are incandescent.
3. Preparation to enclose (2 hours)
Pieces will be incandescent - avoid accidents - don’t place your hand or face over the kiln, keep children out etc. You will now feed the kiln with wood for more 2 hours and then stop feeding, proceed to enclose the fire chamber - place bricks to close the entrance and let the remaining flame burn inside.
If you have few pieces in the kiln - total time aprox. 6 hours. A fuller kiln might need more time , it is estimated that if the kiln is full, it can take up to 10-12 hours in total.
After the firing, let it rest for 24 to 30 hours, then take out the bricks enclosing the fire chamber and later start taking the pieces - be careful, some might still be a little hot.