How to Make a Primitive Kiln at Home
Pottery kilns have been used by people in all parts of the world for thousands of years. By comparison the modern, electric or gas kiln is a rather recent invention, they are nice but expensive to purchase and expensive to operate. A simple primitive kiln such as our ancestors might have used can be made with just materials you have on hand and can be fired with just a few scraps of wood.
I have made two primitive convection pottery kilns, in this article I will share with you my plans for how to make your own pottery kiln and also how to fire one. If you are interested in building your own primitive kiln, read on.
The first pottery “kilns” were probably just surface fires or shallow pits in the ground. This is still an easy way to bisque fire ceramics if you do not want to go to the effort of building a kiln. I have fired pottery this way many times, it works but it uses a lot more wood because it is far less efficient than a primitive kiln and most of the heat just goes into the air without even heating up the pottery.
The basic principle is a two part fire. The first called the “primary fire” is used to build a bed of coals and to pre-heat the pottery to be fired to drive off any remaining moisture in the pots. In the second stage, called the “secondary fire” the pottery is stacked above the hot coals and wood is then stacked over and around the pots. After this secondary fire burns down the pottery is ready to be removed when cool.
This same process can be used on the surface or in a shallow pit. The pit can provide some protection from the wind but may also restrict the flow of oxygen to the fire resulting in lower temperatures than a surface fire.
With this most primitive type of kiln, most of the heat is lost to the atmosphere. Early potters learned to direct the heat to pass over the pottery, thereby using far less fuel, the convection kiln was born!
Simple Convection Kiln Plans
The primitive convection kiln has two main parts, the firebox and the pottery chamber. These are simply stacked vertically in a barrel shaped container.
My kilns were made from puddled adobe which is just earth mixed up into mud and formed in place. Once each layer has firmed up enough, another layer can be laid on top of the first.
The perfect adobe mud has some clay in it but more sand than clay. If your local soil is too sandy it will not dry into a hard lump but will result in a crumbly block, in this case you should add clay to the mix. If your soil has too much clay it will crack when it dries and fall apart, in this case add more sand to your mix. Some minor cracking is acceptable. If you have lots of rocks you can build with stones, I added some stones into my puddled adobe to take up space and to tie the different courses together.
If your mud is not good enough for building and you do not have enough rocks for building either, you could build this out of bricks and mortar. A brick kiln will cost more than a mud kiln but will also be more durable. Feel free to be creative and modify my ideas or building materials to suit your situation and needs. If you look at some pictures of primitive kilns in Mexico you will see that most are made of bricks there.
You will need something to hold the pots above the firebox. I used a piece of expanded metal to act as a shelf to stack the pottery on top of. The ancient pottery kilns of Mexico use a column in the middle of the firebox to hold bricks in place that the pots are then stacked on.
You will want to use something on the top of the kiln as a damper to keep the heat from just flowing freely into the atmosphere. I have used cement-board and bricks in the past. Whatever you use must be made of fireproof materials because it will get very hot in the course of a kiln firing.
If you build your kiln out of natural mud like I did, make sure you allow the kiln to dry thoroughly before you fire it up to prevent excessive cracking. When the kiln was almost completely dry I built a small fire in it and kept it hot for an hour to drive off any remaining moisture before I fired and got it real hot. If you live in a damp climate you will want to protect your kiln from moisture with a tarp or other means when you are not using it because moisture can destroy your mud kiln over time.
Firing the Convection Kiln
Firing in a simple convection kiln is many times more efficient than an open firing pottery. I can often fire bisque ware in my primitive kiln using just one armload of sticks.
Because it is so efficient you will need to be careful that you do not heat the pottery up too fast which can cause cracks and breakage. I usually add the pottery to the pottery chamber then built a small fire in the firebox below with some twigs and small sticks. I keep this small fire burning for at least a half hour to 45 minutes to let the pottery and the kiln warm up slowly.
Once the warm up period is over I start stoking the fire more little by little. If you use a thermocouple with your kiln as I do, you will notice the temperature climbing rapidly at this point. The longer you can keep the firebox burning hot, the higher your temperature in the kiln will be. My small kiln sometimes runs out of room in the firebox before I get up to my desired temperature. In this case I need to remove most of the coals to make room for more firewood.
The smoke coming from the top of your kiln can tell you a lot about how the fire is burning. If it is white smoke or clear, that indicates complete combustion and is a good sign that you are operating at peak efficiency. If the smoke begins to turn dark grey or black, that means that incomplete combustion is taking place and you need to allow more oxygen to get to the fire. You may try fanning the flames, hooking up some sort of blower or removing some more coals to make more space for oxygen to flow into the firebox.
After you have reached the desired temperature you can leave the pots to cool in the kiln. An adobe or stone kiln like this has a great deal of thermal mass which will allow it to stay warm for days after a firing and will let the pottery cool down slowly. Be aware of the weather as rain or snow at this point could cause the hot pottery to break. If the weather looks threatening you might be best to cover the top of the kiln as completely as possible with your damper.
Learn More About Primitive Pottery Firing
If you build a primitive convection kiln as shown above please leave a comment below this article with your thoughts and ideas so we can all learn from each other. If I was going to build mine again I would make the firebox longer so I can get more fuel burning at one time.
If you are interested in learning more about open firing pottery without a kiln then check out my Outdoor Pottery Firing 101 class which will teach you all the ins and outs of firing pottery in the great outdoors. I also have a number of blog posts with more information about primitive pottery firings, you can see those at this link.