Lets keep it simple. Plenty of stuff out there covering The Lime Cycle etc. I hope to just point out a few things in order to qualify why we do the the practical stuff like curing and how important it is to do it right. Phew..
The Lime cycle in a nutshell: The Lime stone is mined and processed and after application as a mortar, it returns back into limestone. Some buzzwords you will encounter are simplified here in the process of making “Lime putty” or “Lime slurry”.
Listen up… Lime rock (or pure sea shells) is calcium carbonate plus some other elements like magnesium carbonate to various degrees of composition.
So if you heat it up, that is ( “burn” it as its sometimes called, or calcine it), it tuns into “Quicklime”. Which is Calcium oxide. Note, carbon dioxide is driven off during this process. In the curing process the carbon dioxide is reintroduced back through air and water, in a process known as carbonation, (thus the term “air lime”) and also the reason to pay attention to the curing process.
If you now add this quicklime to water (without saturating it), it turns into Hydrated lime, or calcium hydroxide. Sold in bags. Adding this hydrated lime to water will make lime putty. Age it. The longer the better. Not so bad so far hey?
OK. We are looking for high calcium hydrated lime. Air Lime is classified blah blah but of special importance is that in America high calcium hydrated lime is classified as class “N”, due to its poor water retention. It has poor workability and requires long soak periods. It’s produced at atmospheric pressure. Less than 5% magnesium carbonate.
The other air lime we hear more of is type “S” which is low 70% calcium oxide and the balance is magnesium rich. Type “S” is hydrated under pressure with enough water added to it to react with the quicklime without saturating it. The problem with type “S” lime is that if it is not fresh the carbonation process may have already begun. So slaking it and storing it in a putty state until you are ready to use it will stop the carbonation process. The lime needs air to carbonate, remember? Admit it now, you are glad you read and understood what slaking is and why it’s done…
Aged putty should be cream like, quite thick. To slake lime, add the lime to water placed in a large drum/container. Mix with a paddle driven by your electric drill. When the mix is thick, add about an inch or so of water on top of it to exclude the air. Seal the can to exclude air.
Practically, high calcium lime binds better than, as well as carbonates quicker than type “S” lime.
Now you know why I want to use high calcium lime. Add water to quicklime (exothermic reaction, can be explosive, but controllable). Woo Hoo, drama 101… Add water to the resulting hydrated lime to make lime putty, again add water to store in the putty state. Why purchase all that water? Safety is a good reason. Many people have died in the lime making business, especially overseas where its been used for centuries in large quantities.. pyramids, great wall of China).
Here’s the best reason to use high calcium lime. Beautiful luminosity of the limewashed surface. Light refracted through calcite splits into two rays, one fast, one slow, resulting in a brilliant stunning appearance.
Hopefully this gives some background so we can pay more attention to the practical side of the process.
Now if you cannot purchase high calcium lime, the option is there to make your own using using high calcium lime rock or sea shells, a good and in my case, readily available and cheap way of obtaining high calcium lime. I will post the costs quoted by suppliers and see how it all pans out.
I took a drive West down Hwy 98 (if you must know) to go to Eastpoint (on the Gulf Coast, somewhere in Florida..) to buy a load of oyster shells. $20 a yard. (over here they call it “yard” not cubic yard.. one is linear? Get it right man…ha ha) Less than half way there I came across a seafood restaurant and lo and behold, the owner let me have as much as I need. Free. Now that’s the spirit of reusing someone else’s discarded “trash” for sure. The price was good.
I wonder if a Ford could handle the load? There’s enough there to finish the job and plenty of stockpiles of free shells along the road if one of you goes to collect the balance of this lot? Only kidding…
Next we will knock up a rocket kiln to make quicklime. Stay with me here ….
Back to “101” little break we had… Lime wash is covered in detail in the practical section.