Making lime with Primitive Technology

Making use of the unoccupied shells of native rainforest snails around his original land, Primitive Technology makes lime mortar by firing them in his pottery kiln, slaking the calcined shells with water so that they disintegrate, and then mixing them into lime putty that’s water resistant after it dries. The material is similar to the materials used to mortar bricks and tiles together.

When heated above 840 degrees Celsius, the lime decomposes into calcium oxide (CaO) or Quicklime and releases carbon dioxide (CO2). When water is added to the quicklime it becomes calcium hydroxide Ca (OH)2 or lime putty. From here the calcium hydroxide can then be shaped into a form and allowed to set. Carbon dioxide enters the lime putty as it dries causing it to turn back into calcium carbonate. The new calcium carbonate has then set, remaining solid and water resistant.

Of the slaking process, he writes:

An exothermic reaction then ensued. Heat was produced as the lime quicklime turned into slaked lime. The water heated up creating steam and the shells decomposed into a white paste. The paste was stirred and crushed pottery was added to it as an aggregate (sand is normally used for this, I just had a lot of old potsherds lying about to dispose of). This lime mortar mixture was then formed into a block shape and left to dry. It took about a week and a half to set as we have had extremely humid, wet weather. The block was observed to have set demonstrating its properties.

Lime is usually found in limestone rock that’s “composed mainly of skeletal fragments of marine organisms such as coral, forams, and molluscs,” but it can be sourced from newer sources of the materials, too.