Primitive manufacturing: my first wood fired kiln.

Welcome, all you bright and beautiful builders! For todays post, we'll be playing in the mud again, and exploring one of the most fundamental building materials in human existence: clay. To build the kiln, I'll be using unprocessed clay dug straight out of the ground, mixed with water, and placed. To get straight to the build details, skip ahead to the paragraph after the first picture. If you want to read a random rabble-rouser's reasonings...

It would be hard to overstate how important clay has been to human existence. The ability to build rodent proof food and water storage, as well as long term waterproof housing, opened up almost as many new opportunities for humans as fire had. Learning to process, work, and fire clay is what set humans on the path to mass production. It was the first thing we discovered that allowed us to not only quickly bring our ideas to life, but to then be able to make them permanent (at least by human standards).

I don't mean to disrespect fire, that was definitely the original game changer, and without it, clay is little more than a flaccid bookmark for ideas, borne away by the first hard rain. Fire is what turns clay to stone, even to glass. Without fire, we wouldn't even have been able to feed our big brains enough calories to figure out what the hell to do with all this clay.

By all this clay, I mean it's pretty much the most abundant substance on earth. There is some form of clay pretty much everywhere on the planet. I only say 'pretty much' everywhere because I haven't seen or studied the whole planet. It exists everywhere, in my experience.

I wanted to learn about working with clay because my land is mostly made of it. The best thing to use, when you can, is whatever you already have a lot of, and you can use clay for a LOT of things. I have so much of it that it makes managing drainage a bit difficult on the property. I also have a lot of plans for this property that require building materials, so I consider it a beautiful problem.

This project is where I learned the things I needed to know to move on to my rocket stove builds. I used it as a test to see how my soil would hold up without any processing or additives, to get a better idea of what sort of processing and additives I would want to use for the stoves. I also wanted to see how well my processed clay would fire, and for that I needed a kiln. I always like a project where I can do one thing, but get many things done.

After I'd finished my testing, I was still able to use the kiln as an incinerator for a while. This really helped me cut down on a few of the local poisonous weeds, like the nightshade. It also worked well for burning big pieces of rotted wood, which had been the breeding ground of our slug problem. Another happy by-product was a lot of high quality hardwood ash, which I used as an additive in later clay projects.


I chose a spot for the kiln on the property that I acquired next door, where I had been digging out some good topsoil I found. I had reached a point where the soil had too much clay for the garden, but there still weren't a lot of large rocks, so I figured it would be an easy excavation. Like every other hole I've dug here, this one had an unpleasant surprise waiting for me. At first I though this was just another large tree root, but it revealed itself as an entire tree that someone buried here at least 20 years ago. It's buried deep enough to be remarkably well preserved, so at first all I can do is dig around it.


The pile of dirt in the lower right corner of the picture below is what I excavated where I'm building the kiln. I wanted to dig it into the hillside to take advantage of the insulating properties of a large mass of earth. I also hoped this would regulate temperatures inside a bit, and help prevent thermal shock. For this mix, I'm just making a crater in the pile, dumping in a couple gallons of water, and turning it with a shovel until it's a workable consistency. The grates were scrap that I brought home from work, and the one on the ground is covering a hole I dug for water to gather, so I won't have to go all the way back to the house for mixing water.


I built the fire to burn the buried tree out of the way, and to dry the clay quickly so I can keep building. The walls of this firebox part of the kiln are about 12" thick, so there's no need to be terribly delicate about drying it.


Once the firebox is dry enough, I set my water hole grate on top of it and begin building around it to make the sides of my kiln. To bridge across the gap in the front, I placed a few sturdy twigs across the opening and piled clay on top of them. The sticks will last long enough for the clay to dry out, at which point it will hold its own weight.


The kiln walls aren't as thick as the firebox walls were, and I want them to stay somewhat straight, so I have to let each few inches dry completely. If I don't wiat, it will be deformed by the weight of the next layer and bulge out at the bottom. Fortunately, I have PLENTY of wood to burn.


It got to be bigger than I needed it to be, but I figured I might as well use everything in the pile that I dug out. With the fire going full force, I was able to dry this fast enough to build the entire kiln in two days.


Below is the finished kiln. It's not terribly pretty, but it operated well with no maintenance at all for over a year. The funny looking colorful bit on the left side of the picture is an old sheet of steel I found on the property, with a target painted on it for playing with my air rifle. I have better targets now, so this will get repurposed as the lid for my kiln.


For test firing, I have some pinch pots the Hedge Witch and I made with some of my processed clay, that we've pre-fired in our toaster oven. We both really enjoy working the clay with our hands, and this past winter I finally got the rest of the junk I needed to build us a proper wheel. Hopefully I can get that project built early this summer.


They look a lot more humble inside that big kiln! I didn't really know what I was doing for this, and I didn't take nearly as many pictures as I should have. There were a lot of problems with cracking when I fired the pieces, due I think to a combination of problems with the clay body (not enough grog) and irregular temps in the kiln. This one is definitely colder in the corners, and I've decided that the upgrade will be round.


For my second firing, I did a little research and read that filling the kiln with wood can help prevent cracking from thermal shock, as well as make some nice smoke patterns on the clay. I had no luck at all with the patterns, but did get less cracking on my fired pieces.


As you can see, the kiln developed some significant cracks after the first real firing. This probably exacerbated the problems causing my irregular tempuratures. One of the reasons that I picked this location is that it is distant from the house and the treeline, so if the kiln fails and my fire gets out of hand, it won't likely spread any farther than the fuel I've gathered to feed it. Despite how bad it looks, I ran out of time to spend on this long before it actually collapsed.


While firing, the top gets covered with my lid, and I pile a bunch of dirt on top of that to help hold in heat. The logs piled in front of the fire are there to cut down on cold air getting sucked into the kiln, as well as to help keep heat in.


The big clay ball was a test to see how deep the clay was becoming vitreous. The cracked up lid had a primitive glaze made from wood ash that we were trying out, but the kiln did not get hot enough to properly set the glaze. Hopefully when I build the upgrade, I'll be able to get up to glaze temperatures.


A couple of the small clay bowls came out pretty good, though we've broken them all by now. The thicker one in the picture below lasted for about 4 years, before it finally got knocked off a dresser.


I find lots of pieces of broken glass on the property, and threw several in one of the bowls, just to see what would happen. The result is that they melted into these glass beads and blobs, They don't have any sharp edges left, so we use them as decorations around the yard and house.


This is what the clay ball looked like after I cracked it open. For as fragile as the bowls were, this things was a monster to break. It took three good whacks with the hammer to open this sucker up. You can see that the vitreous shell is very uneven, but it did get pretty deep in spots. This was after firing for 6 hours, if I remember correctly.


I tried encouraging a lot of people to try this project, or others like it, when things first started locking down a year ago and folks were going stir-crazy with their families. I don't know how many tried it, but this can be a really fun family activity, with just a little supervision. Even the fire is safer than a typical campfire, and this can be a great way to teach kids about fire safety, as well as a valuable SHTF skill!

I hope you all enjoyed! For something so simple, clay is an infinitely fascinating and complex material to work with. My journey will continue, and I hope you all come along for the ride! Can't wait to see you next time!

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