The Next Step - Extending My Excellent DIY Mediterranean Kiln

Winter 2025 / 26, I worked with this DIY Mediterranean Kiln made of expanded clay blocks:

Extending The Excellent DIY Mediterranean Kiln

Last winter’s kiln was a good experience!
And it’s time to take it one step further: the small size of the fire chamber needs to be addressed. And if it never goes higher than 1000 °C / 1832 °F / Cone 06, I think the Lightweight Expanded Clay Aggregate blocks can survive quite a long time.

Read the same warning as for the first kiln:
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 safety aspect, and do not exceed the material melting point.

The new DIY Mediterranean kiln: Some of the stones are new, some old, and now they are all rearranged, which makes the kiln look a bit mottled. Nevertheless, it works flawlessly. It differs from the first kiln by doubling the size of the ware chamber. The old one had a 1:1 ratio between firebox and ware chamber, so now the temperature rises slowly and with fewer crazy temperature spikes. Still lightning fast for a kiln.

This kiln design needs 3 special cut stones; that’s just a 2 minute work with a hard metal saw.

Here doubled the space in the wares chamber.

Testing different firewood, and I learned this didn’t work:
A lot of branches broke off last winter from the heavy snow, and they had all summer to dry up. But without a roof, the branches really never get dry enough. I was not able to exeed 400C with branches picked up from the ground; too much heat was needed just to vaporize water into steam (now that may be the case in the mountains in Norway. Steve Harrison does exactly so in his book “Laid Back Wood Firing”, in Australia. So climate makes a difference. The widest logs (no matter how dry) wouldn’t work either: Blocking the airstream in the firebox, making large chunks of amber, and taking hours of firing before they fall apart into smaller chunks.

No more half-dry branches and huge logs for me; I did hope I could save some money by using what I got in plenty the first hours of the fire cycles, but no more.

Wet branches make a lot of smoke.

Extending the excellent DIY Mediterranean kiln

When the flames ignite first after they exit the kiln, it means there is no oxygen left inside the kiln; this is a sign the kiln is screaming for help: Increase the airflow by raking out the amber choking the passage, and get rid of the oversized log so fresh oxygen can flow freely again.