Expanded clay (LECA) lightweight masonry block
A warning: Lightweight Expanded Clay Aggregate blocks are designed to build houses, it is not designed for making pottery kilns. Though it works as described here for me, consider every safty aspect, and do not exceed the material melting point.
The Mediterranean Kiln Made Simple
Using Lightweight Expanded Clay masonry blocks (LECA)
Stoking the Mediterranean Kiln
The Mediterranean two-chamber kiln is a simple, jet brilliant construction; the kiln has a horizontal, long firebox that restricts unheated air from entering the separate pottery chamber. Over the firebox, a grate or perforated plate, and above that the pot chamber.
Also read these articles:
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How to build the Mediterranean Kiln
Use 23 expanded clay blocks: 50x25x10 cm, where only one of them has to be cut to fit the design. Some steel wire is needed to keep the kiln together. This is important since the pottery chamber’s outer diameter is 10 cm wider than the firebox. I stacked this kiln without mortar. A wobbly base makes stacking the kiln difficult and will give glitches between the blocks. To keep the foundation straight, I (should have) laid the foundation on top of two horizontal steel rods I have from an old bookshelf.
This is my pottery kiln design using expanded clay blocks:
In my local store for building supplies:
23 LECA blocks: 50x25x10 cm. 5,5 USD each block = 126,5 USD in total, that’s a cheap kiln!
But remember, this is an experimental kiln; it will likely not last forever. I pay 60 USD to hire a professional kiln for each firing, as a comparison.
LECA stands for "Lightweight Expanded Clay Aggregate", it's made of burned clay and withstands quite high temperatures (up to 1000 - 1100 degrees C). The combination of air pockets and clay makes it both lightweight and a good insulator.
Steelwire keeps the kiln together.
The pottery chamber: I have cut the length of one LECA block to fit inside as the grate. I did not senter the grate-block, but made the biggest opening in the back of the kiln to draw flames all the way in, and a small opening in front.
Firing the Mediterranean Kiln
Firing this DIY version of the Mediterranean two-chamber kiln is really easy! This firebox is 1m deep, 25cm high, and 30cm in width, making it a spacious firebox. Just keep it filled with dry wood and make sure there is room for the airstream, and the kiln just does the rest by itself!
The Mediterranean two-chamber archeological workhorse:
Though it’s often referred to as the Mediterranean kiln or the Roman-Greek kiln, it was widespread in Iron Age Europe and prehistoric times. This quite simple design appeared across Greece, Rome, Mesopotamia, North Africa, and parts of Asia. And widespread for a reason, I would say! A kiln form so stable and efficient that it barely needed improvements for the next 2’000 years, and is still in use today.
Practical experience:
My first test-fire; reached orange pots (8-900 degrees C) in no more than 3 hours, and that was as far as I wanted to go the first time. The expanded clay blocks are greate isolaters with a low mass, meaning it also takes really short time to heat up.
None of the blocks deformed or cracked in the firing; that’s good, but I don’t know if the material will decay over time when fired many times.
My second fire; I had the wind from the back (wrong angle), but no problem. This kiln design just feels absolutely rock solid! I put in 3 logs of wood every 20 minutes for 4 hours, and reached 1000°C.
Some LECA grains crack when heated at high temperatures, falling down as black spots on the pots. It’s fewer black spots in the second firing, but still some, and they get’s stuck in the melted glaze.
My third fire; seems like no more black grains falling from the kiln walls, that’s good, but the grate-block (the only block that takes heat from all sides) starts to crack, but is still keeps together!
Now the lightweight expanded clay blocks start to deform and lose their shape a little due to the heat, and we can see some glowing red cracks between them.
Burning lively, only yellow flames are coming out of the kiln. Shure a kiln without a pipe makes smoke
Since it’s winter here, most of the smoke in the first hour is just steam from melting snow and ice.
Draft (or the Venturi effect) is a mystery. By closing the opening to the fire almost completely, the heat loss is reduced, and the amount of new, cold air is reduced. But the air speed increases and gets more organized. And the fire just loves that. Here I am using a block in front of the fire-chamber to make a draft.
1000°C reached, but I would say 950°C, peak 1000°C. I did not have time to set up my best temperature-measuring instrument, and had to trust the heat gun. Though the Mediterranean pottery kiln is easy to handle and has a reliable performance, it is an updraft pottery kiln and would likely not exceed 1100 degrees Celsius (and I will not recomend to exceed 1000 degrees Celsius with LECA blocks).
The Mediterranean two-chamber kiln
Firing the Mediterranean kiln in the Blue Hour, before everyone wakes up.
I fired to 950 (peak 1000) degrees, added 2 more logs, and closed the kiln in the best possible way to make a reduction atmosphere. With nowhere else to go, the heat was now leaking out between every brick. Though the base has been cold through the hole firing, the temperature under the kiln now started to rise, and melted the ground under the poorly secured foundation. The kiln was cracking up as it was sinking. Lesson learned: Reduction firing in a kiln that needed the frozen ground to stay frozen, was not the best choice.
Though I closed the kiln, some small flames still made it between the blocks.
Also read:
/how-to-build-a-wood-fired-kiln-oil-barrel/
The Mediterranean Kiln Made Simple
I always wondered why archaeologists find so few pottery shards from ancient times in the Nordic regions, but as a guess, I would say winter is to blame; you just can’t work with clay in minus degrees, and the summers were short and busy.
Also read:
exarc.net/ixperimenting-ancient-greek-pottery-production-process
colorado.edu/classics/ancient-greek-ceramic-kilns
Some inspiration from YouTube:
The Mediterranean Kiln Made Simple – 2026