The Lime Cycle
The reason we can even use plaster made from limestone so effectively for thousands of years, is due to some very interesting chemical processes that were observed and guided by human ingenuity.
Our ancient ancestors figured it out, and today, the very same production processes are employed, even if on an industrial scale and using more modernized equipment.
At least 12,000 years ago, humans began turning rocks into a malleable and spreadable putty which then turned back into rock. How?!
Through a little bit of stone alchemy known as The Lime Cycle.
Stage 1: Calcination
Limestone is made up of mostly Calcium Carbonate - chemically denoted as CaCO₃
Now, this is weird, but the rock itself remains a solid rock as long as the Carbon Dioxide inside the rock has the same pressure as the CO₂ in the air around the rock - a state known as equilibrium. What was discovered is that if these specific rocks were heated to very high temperatures in an oven or kiln-type structure, they would change and turn into a pile of crumbly powder. What’s going on?
Today we understand the chemical processes at work in what they observed.
As the temperature of the rock approaches 1500℉, the pressure of the Carbon Dioxide inside the rock rises significantly. In this enclosed environment, the Oxygen levels in the air around the rock drop. The result is an extreme imbalance in these pressures. Gases go from areas of high pressure, to areas of low pressure - and so, out goes the CO₂ from the rock.
What is left over is a different chemical known as Calcium Oxide (CaO).
Calcium Oxide is also known colloquially as “Quicklime” due to its volatility and reactiveness. It is very unstable, however our human progenitors continued experimenting and observing to figure out what they could do with it. The result was stage two of the Lime Cycle, known as “slaking".
Stage 2: Slaking
Slaking is just a fancy word for adding a bunch of water. What was discovered is that if they inundated this powder with water, it would boil and heat up, and then eventually stabilize into a smooth, spreadable paste-like substance.
Again, thanks to our modern scientific understanding, we can describe exactly what is happening in this stage of the Lime Cycle.
As the Calcium Oxide is slaked, chemical reactions cause the Hydrogen and Oxygen atoms to be picked up, changing the Calcium Oxide into another chemical substance known as Calcium Hydroxide - Ca(OH₂).
As we continued to develop this process, it was found that we could create this product in two different forms. In one form, water was added until the smooth putty was formed, what is referred to as “lime plaster” or “lime putty.” In the other form, just enough water to stabilize the Quicklime is added which hydrates the lime, but results in a powdered form of Calcium Hydroxide - a material that could be further hydrated to make lime plaster later. Today, we still manufacture lime plaster in these two forms using the same exact methods.
So, now we had this putty to work with and observed that after we spread it onto a surface, it would dry and return to its original hardness. Again, how?! This brings us the final stage in the Lime Cycle, carbonatation.
Stage 3: Carbonatation
It sounds like a word a drunk guys says to you at a bar while explaining how stuff works, but carbonatation is actually the final stage of the Lime Cycle.
As the Calcium Hydroxide begins to dry and cure it loses water molecules through evaporation. As this occurs its chemical bonds are also looking for carbon atoms. It turns out, there is a ready supply of carbon all around it in the air in the form of CO₂. As this process continues, the Calcium Hydroxide begins to react with the carbon atoms in the air. As the CO₂ is absorbed by the plaster, the Carbon atoms are integrated into its chemical structure, while Oxygen atoms are evaporated away with Hydrogen atoms in the form of water vapor. In the end, lime plaster absorbs and traps more carbon atoms than were emitted during its production.
The result is the Calcium Hydroxide transforming back into its original form, Calcium Carbonate - or, Limestone.
We took rocks, turned them into a different thing, then to a different thing, and then watched it all turn back into the original rock. Wild!
The amazing thing is that this ancient discovery and material works because of characteristics that are perfect for the issues, concerns and goals have have today.
It’s just rocks and minerals - nothing synthetic, dangerous, volatile or unhealthy; it won’t ignite or provide fuel in the event of a fire either
It contributes to reducing environmental Carbon and creating a greener planet - due to its natural ingredients and carbon capture, lime plaster is a major contributor to green building certification programs
Lime is incredibly alkaline, making for a surface with the same pH as bleach - a total hellscape for mold, fungus and microbes that can’t survive such conditions
Unmatched durability and longevity - timeless style matched with the fact it actually gets harder over time
Sustainable & recyclable
