Did you know that you can create a rudimentary furnace that can reach temperatures in excess of 1200 degrees Fahrenheit with some clay, filler and water? It will take some elbow grease, but this is a project that you can accomplish in just a few hours. The finished product can be used over and over again, and it can be an efficient way to soften or melt metal or extract ore from rocks. Take a look at the basic design below, and feel free to improvise and apply the same principles to construct one that is an ideal match for your specific needs.
Getting Started
The first step is to choose an appropriate site for the furnace. Keep in mind that it will be a few feet wide and around 4-5 feet tall when finished, so it’s important that you keep it away from any combustible items that may be nearby. Next, dig out a shallow hole that’s slightly larger than the diameter of the furnace. Place a bed of flat rocks in circle in the center of the hole that will represent the base of the furnace, but it needs to be big enough cover the outer edges of the walls.
Next, dig a hole that you can use as a pit for mixing the clay, water and filler material. Add in the clay, water and filler and start mixing it with your feet or a long, thick stick. Add more water if the mixture is too thick, and add more clay if it is too thin. When finished, scoop a large amount with your forearms and place it atop the stone foundation. Flatten the clay over the entire surface of the rocks until you have an even layer that’s around 2-3 inches thick. Let it dry before moving on to building the walls.
Building the Walls
The next step is to build a mound of clay that’s a couple of inches thick and tall to create a circle that goes around the foundation and touches the edge. Press it in place, and leave a gap that’s about 3-4 inches wide at the ends. Repeat the process for the second layer, using a stick as a spacing guide for the main circle as well as the side gap. Add another layer or two of nearly-complete circles before placing some twigs atop the gap. Then, you can continue to repeat the process by making complete circles until you’ve reached the top of the furnace.
Building the Entrance
Next, take some clay to create a strip that is about 1-2 inches thick and high, and bend it into a circle on top of a flat surface. Let it dry slightly before adding each successive layer, smoothing out the strips as you go in order to create a smooth, solid canister-like finish. Make it about 8-10 inches long and just wide enough to fit into the top of the side hole you’ve made earlier. Take a mound of clay and use it to fill in the bottom of the side gap until you can insert the canister and hold it in place. Fill in the holes or gaps with additional clay until everything is sealed up.
All you need to do now is fill the stove to the top with small pieces of wood and tinder, light it up, and wait for the fire to start glowing red to white hot when you look through the side hole. Insert whatever material you want to work with and wait for it to melt down. Keep adding wood to maintain the fire, and you’re good to go.
There will come a time when you will need to empty the furnace of ash and charcoal. Simply break off the side chimney and material beneath, scoop out the debris, and reattach the chimney and plug when finished.
The nice thing about this furnace is that while it may be labor-intensive to build, you won’t have to constantly stoke the flames in order to maintain a high temperature. Consequently, this is a great way to create enough heat in the field to handle some basic metalworking projects as well as to extract ore from certain rocks, and you never know when this will become necessary in a long-term survival situation.