Primitive Technology: Wood Ash Cement & Fired Brick Hut

By | October 31, 2022

Excavating clay from the pit by hammering stakes and collapsing the sides in Adding water and mixing clay into lumps for transport Into the mixing pit Digging sand to mix with clay (stops clay cracking as it dries) Mixing in sand Forming the brick Turning the bricks as they dry Collecting fire wood. 75cm long pieces ( the length of the kiln fire box) Fire by friction Drying the bricks (they need to be bone dry before firing or they explode due to steam escaping) Stacking the kiln. 50 bricks can fit into one firing. The kiln can be stoked from both ends and it fires quickly Some bricks on top to keep the heat in Each of the 14 brick firings took 2.5 hours to complete Storing bricks around workshop before use Digging the foundations for the hut (a 25 cm deep/wide trench around a 2 x 2 m floor area) Newly fired bricks Compacting foundations Placing bricks in Digging out wood ash left over from firing the bricks Sifting the ash of stones and charcoal Mixing the ash with water and forming into pellets After multiple firings the pellets add up The pellets dry hard before re-firing Time to calcine the pellets to before being able to make them into mortar The flames move through the pellets calcining them (the heat and oxygen converts the calcium carbonate in the ash back to calcium oxide) The pellets must glow red to orange to calcine (the hotter the better) This took less time than a brick firing, about 2 hours. Now, after calcining, the pellets are weaker and crush easily into a powder Digging sand to make the mortar mix 3 pots of sand to one pot of calcined wood ash Make a well in the sand and pour in the ash Add water and mix (don't used hands like I did, it's a bit caustic) Applying mortar to bricks

Also, you should soak the bricks first to make the mortar stick better. Dry bricks suck the moisture from the mortar. Second layer, mortar on top of the first bricks and laying bricks on top. Foundation level is 3 bricks or 25 cm deep. See, I got lye burns from handling the mortar bare handed. That's why you use a stick to mix it and a trowel to spread it. Wooden trowel to apply the mortar A half (broken) brick to start the door way. First layer done (I did about one layer a day, mixing the mortar as I needed it) It rained a bit as I worked but it didn't seem to affect the brick work or erode the mortar Putting in a window A few weeks passed because I ran out of bricks and had to make more (hence the change in wall color) Gable end walls were completed thusly Here's a sample of wood ash mortar that has set. Note how it doesn't dissolve in water. This is a subtle yet important advantage over mud as a building material adding to the longevity of the structure Cutting lawyer cane to form a frame for making roof tiles Split the cane and then kink it to form a trapezoid Forming a roof tile Folding the tile over a curved mold Laying the tile out to dry Tiles into kiln The kiln does 32 tiles per firing A tile firing takes 1.5 hours (less thermal mass than 50 bricks) I did 8 firings (lots of spares, used the ash for cement as well) Cutting purlins for the roof 10 purlins 2.75 m long The purlins simply sit on the gable ends with the force direct vertically down onto the wall, thus avoiding lateral forces that may push the wall outwards The purlins roll like wheels if unsecured. So they were mortared in place to prevent movement (broke a few tiles figuring this out) The optimal roof angle is 30 degrees, steep enough for the tiles to shed rain but not enough for the tiles to slide off. Weight and friction are enough to keep them on. Overlapping layers of tiles facing up act as chutes to shed the rain, while tiles facing down cover the gaps between these columns of tiles. This process was tedious, lots of tiles broke due to the poor quality clay. In future I'll use better quality clay for roof tiles, this clay is ok for bricks though. Finished hut. The mortar pit is now a fire pit. A rain storm tests the roof The roof is mostly water proof, I fixed some minor leaks later with with pieces of tiles. I was able to keep a fire going and the ground was dry and dusty despite the rain. After the storm

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