Former Technology: Lime
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Infomation
Description
At the old hut site (the new one being temporarily cut off by flooding) I made lime mortar from the shells of rainforest snails by firing them in a kiln, slaking them in water, mixing them into lime putty. Limestone is basically calcium carbonate (CaCO3). The general source of lime is limestone and various other calcareous minerals, though shells, egg shells and coral are other sources of lime (for more information see video on Corporals Corner channel: https://youtu.be/tOhAfaFboNU or Skillcults channel: https://youtu.be/jOxaOTUGuKo). 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.
In my local geography, calcareous rocks such as limestone are absent leading to a difficulty in acquiring the feed stock for lime making. However, I was still able to make lime by collecting the shells of large terrestrial snails that are native to the rainforest here. The unoccupied shells of these snails were gathered up and stored at the hut. Fire wood was gathered and packed neatly into the kiln. Importantly, the firewood was stacked on top of the grate rather than underneath it in the firebox as is the normal procedure for firing pottery. Using an ordinary updraft pottery kiln in this configuration allows it to reach much higher temperatures than would be possible during normal use. The wood was lit from above and the fire burned down towards the grate. Alternate layers of shells and wood were added on to this burning fuel bed. After adding the last layer of wood to act as a “lid” to prevent heat loss from above I left the kiln to finish on its own, unsupervised. The whole process took about an hour and a half.
When the kiln had cooled down a few hours later, I took out the calcined shells. Not shown in the video was the fact that some shells got so hot, the dirt stuck to them turned into slag and fused to them, possibly with the lime acting a flux lowering its melting point. This extreme heat (+1200 c) should be avoided as the over burnt lime becomes “dead lime”, unable to slake in water. Most shells were still useable though. They were taken out of the kiln and had water added to them. 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 pot sherds 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.
What I created is actually lime mortar, typically used for mortaring bricks and tiles together. It’s basically the ‘Glue’ that holds together the building blocks of masonry structures. From my research 20 kg of lime mortar is used on a 1 m square section of brick wall. 5 kg of lime to 15 kg of aggregate (sand, grog etc.) per a 1 m square section of bricks. The shells, though large, are not terribly abundant. A method for finding shells efficiently needs to be made before considering making lime mortar in this fashion. From my experience sand bars in a creek sometimes accumulate snail shells from higher up in the mountains. In these spots, water velocity decreases and shells in the water tend to drop out of the water column. Additionally lime may be partially replaced with ordinary wood ash in mortar without a corresponding decrease in strength. To conclude, making lime in a land without limestone is possible but can be problematic when trying to do so on a large scale.
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Transcription
Terrestrial rain forest snail Looking for shells Unoccupied shell (i.e. the snail died) Shell pile Fire wood Wood pile Back at the old tiled hut Kiln Stacking wood.
Fire sticks to make fire Blowing on hot coal Hot coals from subsequent fire Fire burns down from top towards grate Shells added to fuel bed Layer of wood added over shells More shells More wood Hot shell fragments shooting out of the kiln causing annoyance.
Hot coals and shells that fell though the grate From my research, burning wood on top of the grate rather than under it produces the highest temperature possible in an updraft kiln (approaching 1400 c) Time taken: 1 hour 30 minutes Removing the cooled down shells a few hours later Adding water to a burnt shell Note the steam coming off the shell. It is decomposing into slaked lime and releasing heat in an exothermic reaction. After a while it turns completely to paste Slaking more shells More steam.
A stronger reaction Crushing old pot sherds for aggregate to mix into lime putty (normally sand is used) Mixing in grog (crushed pottery) ratio of 1: 2.5 lime putty : grog This is basically mortar used for joining bricks or rocks together but I'm just going to make a block of it as an experiment 10 days later the block has set Water testing for a few minutes. The block is water resistant for this length of time. Note however that full strength is developed over weeks, months or sometimes years of setting. Lime
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Author: Author Link: Youtube Link: https://www.youtube.com/watch?v=Ek3aeUhHaFY Category: Channel Name: Primitive Technology Channel ID: 22 Tags: primitive,lime,
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