I want to use lime for several applications in the big building – plaster, mortar, to mix with clay and wood shavings for insulation, and for limewash paints. And by lime I mean non-hydraulic lime, the traditional, breathable and flexible basis of mortar and plaster used from pre-Roman times right up to the Industrial Revolution. Not to be confused with hydraulic lime, which is not so very different from Portland cement (though see comments below).
Making lime mortar and plaster from quicklime (preferable to using hydrated lime), requires a bit of forward planning. Before you can do anything with it, you first have to make lime putty, then this needs time to sit and mature for as long as possible before use. Opinions seem to vary on how long the bare minimum should be – 2 months, 3 months, 4 months – and the Romans apparently forbade the use of lime putty less than 3 years old. But there’s no disagreement about the fact that the longer it matures, the better it gets, so I wanted to get started on making the putty as soon as possible so I could give it at least 4 months. I’m kicking myself I didn’t think of this a year ago, but that’s design-it-as-you-go building for you …
Quicklime (Calcium oxide) is readily available from builders merchants here (Cal viva), bagged and finely ground, and we were able to get an empty 200 litre (55 gallon) oil drum from the local garage from which we removed the top.
Quicklime is highly reactive, absorbing water from wherever it can find it even to the point of exploding, so it’s important to treat it with respect, wear protective gear and have a bucket of water to hand to instantly rinse any that comes in contact with skin.
So to begin …
The oil drum cleaned and half filled with water.
Powdered quicklime was added to the water at a rate of around 10kg a batch and stirred with a length of clean wood.
As progressively more quicklime was added, the water became hotter and hotter from the intensity of the reaction, soon boiling and giving off lots of steam.
After around 50kg had been added, the reaction really took off. Almost literally. Great fun! Big kids’ chemistry set! But stand well back and keep children and animals out of range.
The result? A lovely creamy putty with the consistency of soft butter.
I slaked the remainder of the 80kg of quicklime in small batches in a metal bucket, then added this to the drum, making for a much more controlled reaction. Volcanos are fun, but only when there’s room in the container for them. We’re not ready to plaster the walls just yet.
After 24 hours the drum had cooled to body temperature and a layer of water had separated and risen to the top. Now it will sit …
João tells me his grandmother always kept a barrel of lime on the go and that it was traditional to do so. It was also common throughout Europe to store lime putty in pits and even pass it from one generation to the next. I reckon I’ll be keeping a barrel here too.