Building a hut with a kiln-fired tiled roof, underfloor heating and mud pile walls

I built a hut with a tiled roof, underfloor heating and mud and stone walls. This has been my most ambitious primitive project yet and was motivated by the scarcity of permanent roofing materials in this location. Here, palm thatch decays quickly due to the humidity and insects. Having some experience in making pottery I wondered if roof tiles could feasibly be made to get around these problems. Another advantage of a tiled is that it is fire proof. A wood fired, underfloor heating system was installed for cold weather. A substantial wall of mud and stone were built under the finished roof. It should be obvious that this is not a survival shelter but a project used to develop primitive technological skills.

Time line: 102 days (21/5/15-30/8/15)

Chopping wood, carving mortises, putting up frame:  10 days (21/5/ 15 -31/5/15)

Using a celt stone axe I had made previously (https://www.youtube.com/watch?v=BN-34JfUrHY) I harvested the timber. 6 posts were put into the ground. The floor plan of the hut was a 2 X 2 m square. The 4 corner posts stood 1 m above the ground and buried 0.25m below ground. The 2 ridge posts were 2m above the ground and buried 0.25 m below ground. The ridge and wall beams were 2.5 m long. These had 2 mortises each at 0.5 m from the ends made using a mallet and stone chisel. These were then fire hardened to prevent the wood splitting. The top of the posts were carved into tennons for the mortises to fit onto. Rafters 1.75m long were lashed together and laid onto the frame and then lashed to it. Saplings for the tiles to sit on were harvested later as needed after each firing.

Building kiln and tile frames: 5 days (3/6/ 15- 8/6/15)

A simple kiln was built with a removable (replaceable) kiln floor or grate. The grate was a clay disc about 0.25m in diameter with 19 holes in it to let flames through it. A 0.25m wide, 0.25 deep trench was dug into a slope and a stone lintel was used to cover over it. Onto this the mud wall of the kiln was built. The inner diameter of the kiln was a bit wider than the grate (about 0.3m) and the height of the kiln was about 0.5m tall. The kiln wall was about 0.12m wide. A fire was then lit in the trench or firebox to dry the structure. Originally the fire box of the kiln had 2 stones with a broken tile resting on it as a sort of grate bar. Wood was fed over the bar while air entered under it. This caused the air to come up through the burning wood so that efficiency was increased. Later 2 rows of mud were put into the fire box and a few purpose made grate bars were put in place to make a permanent version of this. Having grate bars that raise the fuel bed off the ground so air goes up through it increases heat production and fuel efficiency several times. 20 tile frames were made. These were split strips of lawyer cane that were kinked and bent into rectangles. They were 25cm long and 15cm wide.

Rain delay: 36 days (9/6/15- 14/7/15)

In what would normally be the dry season we had over a month of unseasonal rain. Work completely stopped on the hut. Unfired tiles left in the open dissolved in the rain, large amounts of dry firewood were impossible to find and the wooden frame of the hut lay exposed to the elements with mould growing on it.

It was during this time I built the wood shed (https://www.youtube.com/watch?v=ZajpkwDeEYg) to store fire wood and unfired tiles in preparation for the firings to come. Despite the weather I managed to make and fire 20 roof tiles as a test.

Tile making and firing: 28 days (14/7/15-11/8/15)

To make a batch of tiles, clay from the creek bank was dug, mixed with old crushed up pottery or broken tiles and made into 20 balls per batch. A flat stone was dusted with wood ash to stop the clay sticking to it. A lawyer cane tile mould was placed on this and the ball of clay pressed into it and flattened. The surface was dusted with ash and the tile flipped over. The other side then had a tab made into the upper end for it to fit onto the batten. The tile, still in its frame, was then set upright near a fire to dry or left to air if no fire was available. Meanwhile the tiles made two days earlier were place into the kiln 20 at a time (10 at the bottom and 10 at the top) and fired until those at the top glowed at least red hot. Each firing took about 4 hours with the kiln only needing periodic feeding of fire wood allowing me to make tiles for the firing 2 days in advance. The semi dry tiles from the day before were laid against the kiln to become bone dry (slightly damp tile would explode if fired).

A typical day of tile making was divided into a morning and afternoon shift: The morning involved firing a batch of dry tiles while simultaneously making another batch and leaving it to dry. The afternoon shift involved mining, processing clay and collecting firewood.

In total I made and fired 450 flat tiles and 15 curved ridge tiles. It took 25 firings with 20 tiles per firing (the 24th and 25th firing made up for breakages). A 26th firing was done for the roof capping tiles.

The tiles above the firebox got the hottest glowing orange to yellow hot. Those near the top only glowed high red. Some days the wind blew into the kiln and raised the temperature to the point where the some tiles started to soften and sag with some minerals beginning to melt out of them. These tiles were like stone in hardness.

Stone footing for wall: 1 day (14/8/15)

A stone footing was built around the hut for the mud wall to be built on. If a mud wall is built on stone footing its longevity in increased as it cannot wick up moisture from the ground. This only took a day.

Underfloor heating:  2 days (15/8/15- 16/8/15)

A trench was dug into one side of the floor of the hut from front to back and covered with stone slabs. Gaps were sealed with mud and a fire was lit in the front end. The slight incline ensured that the smoke and flames travelled beneath the floor heating it. A short chimney was built at the back to increase the draft and the stones were covered in mud to form a level platform. The result was a slightly raised floor area that was heated from below. This is similar in principal to a Korean “Ondol”, Chinese “Kang” bed or Roman “Hypocaust”. Flames travel beneath the floor heating it and radiating heat straight up into the room.

Wall: (17/8/15- 30/8/15)

The wall was constructed of mud. Originally I was going to dig soil from around the hut to use for the wall but it became quickly apparent that the drain it would leave around the structure would be too large and lead to the structural instability of the hut. So instead I excavated a large pit in front of the kiln for soil. The mud was placed onto the stone footing so that the wall was about 0.25m thick. The first few layers were of mud alone but I started adding stones to the layers to cut down on the amount of mud needed. It took less effort to carry rocks than it did to dig soil and carry water to make the mud. Before building the wall the wooden structure swayed worryingly when pushed by hand. After the first few courses of mud wall however the posts were held rigidly in place forming a solid structure.

Summary

This was the most complex hut I’ve ever built because of the materials involved, the scale and planning and management of resources. The frame was an experiment in the use of mortise and tennon joints- the first time I’ve used them in a structure and it was justified, given the weight of the roofing material. Firing the tiles in small batches of 20 was inefficient in terms of fuel with one large firing being preferable to 26 small ones. If I were to do it again I might make the all the tiles first then stack them in a pile and cover them with mud- a clamp kiln. The advantage of firing the tiles in small batches was that they did not need to be stored before firing in a separate shelter but be made, fired and put in place on the roof as I went. The underfloor heating was an interesting experiment though here it would only be necessary during the coldest months of the year. It was easy to build and would make all the difference to comfort in cold locations. The mud wall was technically easy to build but required much more labour compared to a wattle and daub wall. The benefit of this though was the stabilising effect on the whole structure. The roof wobbled slightly before building the wall but after was held firmly in place. The finished structure is a little dark and needs to be lit using resin fuelled lamps. In future I may consider windows for better lighting. All in all it is a good, solid, fireproof structure that will not decay any time soon.

From Primitive Technology: https://primitivetechnology.wordpress.com/2015/09/05/building-a-hut-with-a-kiln-fired-tiled-roof-underfloor-heating-and-mud-pile-walls/