LIME SQUAD! II: THE SLAKING
Having burned some sea shells into quicklime in photoessay part one, it was time to slake the shells into lime putty.
In the morning we went out to the kiln all excited and grabbed a few well-burned-looking shells for a quick experiment. We put the shells into a dish and crushed them lightly with a spoon and added water. In order to turn into calcium hydroxide, a.k.a. lime putty, quicklime has to undergo a chemical reaction with water which creates a good deal of heat. Well, our quicklime just sat there cold in the water, no churning and boiling :( what a let down… After getting over our initial disappointment it seemed just not right that our lime didn’t react. The shells were completely white through and through. So, we put the shells and water on the stove to heat a bit and that seemed to slowly kick off the reaction and eventually they broke down into lime putty. That was encouraging, but it wasn’t time for the champagne yet.
I had pretty much decided that we should use hot water to slake at this point, but considering the time and energy we had invested so far we wanted a more informed opinion. I called Jeff Price at Virginia Lime Works who generously spent a small piece of his morning in the pursuit of my edification in regards to lime and lime burning. Sure enough, he recommended hot water to start it off when using shells because the structure of shells is less conducive to the slaking process than the structure of stone. The up side is that shells make more lime putty than an equivalent amount of burned stone. I took my page of notes and was ready to rock.
The burned shells were added to an old wine barrel pre-charged with hot water. Continue reading
LIME SQUAD! I: A PHOTO ESSAY ON LIME BURNING
I’ve been interested in lime for a while now. I use it in tanning hides and I want to use it in building. Lime is also used in processing corn into hominy as well as masa for tortillas. Doing things completely from scratch always interests me, so project buddy tonia and I set out to burn some lime and see just how much work and fuel is required for what results. The following is a photo essay on our first lime burn, but first a few thoughts on lime, lime burning and lime users.
A BRIEF DESCRIPTION OF THE BASIC PROCESS
Limestone or shells (Calcium Carbonate CaCO3) are burned for a time until they are calcined, that is reduced to Calcium Oxide a.k.a. “quicklime” (CaO). This releases carbon dioxide into the atmosphere.
The lime is now what is called quicklime and it is quick… quick to react with water in an intense chemical reaction creating heat and converting the lime to Ca (OH)2
To make dry hydrated lime, which is more stable than quicklime, the quicklime is sprayed with just enough water to cause it to undergo most of its reaction and crumble into a powder after which it is bagged. Hydrated lime is used as an admixture to increase the workability of portland cement mortars which, even with the addition of lime, are horrid to work with. Other people use hydrated lime as one would use lime putty that is mixed with water to form a lime “paste”.
To make Lime putty, the quicklime is mixed with a larger quantity of water whereupon the stuff boils like crazy and turns into calcium hydroxide, Ca (OH)2. Lime putty remains as calcium hydroxide as long as it is kept from air under a cozy blanket of water. Under water it only improves with age.
When the lime paste or putty is used it must be dried slowly. As the lime dries, it reabsorbs the Carbon which was driven away from it in burning back out of the atmosphere turning back into limestone (CaCo3) . So, the lime putty is used wherever it is that you need limestone such as in mortar, lime concrete, plaster etc… How cool is that? Continue reading