PRIMITIVE FIRE SCIENCE! Burning Shells Into Lime In a Grass Straw & Clay Furnace -

By: SkillCultPublished: 2 years ago

35, 817 views

514 Likes   5 Dislikes

Intrusting Stuff

In this short video, I build a kiln from about half straw and half clay and use wood to burn shells (calcium Carbonate) into quicklime (Calcium Oxide), then slake that with water into Calcium Hydroxide. There is a longer how to version of this video here:

Support my channel by using this link whenever you shop on Amazon. Free for you, a big help to me!:

Keep me making Content as a patreon supporter:

Subscribe here:

Check me out on Instagram and Facebook as SkillCult and on Flickr as Steven Edholm.

Lime is one of the most useful substances ever! It is used in smelting and refining, processing foods like sugar and tortillas, for mortar and plasters, it is the main ingredient in cement. it can be mixed with milk protein for milk paints and cheese glue, it is used in preparing skins for tanning and much more. Lime is not only easy to make from limestone or shells, it's hella fun!

If you want to know all about lime and it's uses in building, read the definitive book, Building With Lime by Holmes and Wingate.

Shells or limestone are burned at about 900 Celsius driving off the carbon leaving quicklime (calcium oxide). Water is added to the calcium oxide to slake the lime. It creates lots of heat reacting with the water and changes into calcium hydroxide. Calcium hydroxide will keep indefinitely if stored under a layer of water as "lime putty" and actually improves with age. Once exposed to the air and allowed to dry, the calcium hydroxide turns back into calcium carbonate, which is what we started with, thus completing the lime cycle.

The kiln here is invented by me and based on Michael Smith, Author of The Cobbers Companion's, straw and clay wattle system, which was in turn inspired by a traditional style of clay/straw granary from Mexico. This Kiln is called a PET and is just bundles of straw dipped in clay and laid in coils like a coiled pot. The Furnace has some insulation properties from the hollow grass stems, but also some mass from the clay slip, so it gets hot and stays hot. This can also be done in a metal drum.

Shells or limestone are layered in the kiln with pieces of wood and fired with a free flow of oxygen through the vents in the bottom. It burns naturally at around 900 Celsius or 1650 degrees farenheit. Carbon is driven off the shells or stone leaving calcium Oxide or quicklime. The shells are sorted to discard those that are underburned. Quicklime is very dangerous and highly unstable. When warm water is added, it boils violently as it takes on water to become slaked lime putty, or Calcium Hydroxide. This Lime Putty can be stored under water and will not only keep, but it will improve with age. Masons used to make it and store it for use years later.

When the kiln is burned out, all the ashes, pieces of burned clay from the kiln, bits of charcoal and pieces of burned shell are crushed and added to the garden soil.

For More on lime, visit my website SkillCult.

Report form

Related Articles

Related Videos