Snap, crackle and pop
October 30th, 2007 - Posted in bodging, eco-building - by Brendhan|
We wrote a few days ago that the building consent for our eco-garage has been issued. The local council has agreed that lime plaster is an acceptable weather coat so we are able to move onto the next step – slaking some lime. First we had to cut the tops off our collection of 200 litre barrels and clean them.
One of the reasons for using a lime plaster is that it is almost carbon neutral over its entire lifetime. Before the widespread use of Portland cement during the last 19th century, lime was the critical ingredient in mortars, renders and plasters. Its main advantages over cement are flexibility and permeability. Before we left the UK Brendhan went on a course run by the Low Impact Living Initiative and the Cornish Lime Company to find out more about it, so here’s a quick lesson… Limestone is converted to quicklime by heating it up to at least 825°c. This process turns the limestone (calcium carbonate) into quicklime (calcium oxide). Quicklime is an unstable white compound that is very caustic and reacts violently when it comes into contact with water. When the quicklime is added to water a chemical reaction occurs which converts it into lime putty (calcium hydroxide) – this is called slaking. A rather exciting exothermic reaction occurs and the mixture bubbles and spits and gets really, really hot.
Unfortunately the view is not perfect as we had to make sure that the camera was at a safe distance but this video clip shows what happens when you don’t stir it enough.This is what we have been doing over the last few days (and I can tell you it’s hard on the shoulder muscles) and we have done 6 of our 16 barrels. We will be continuing to do more whenever the weather is dry until we slake the whole 1,000kg of quicklime we bought from Taylors Lime in Timaru. In 3 months time we will mix the lime putty with sand and plaster our walls with it. As the plaster cures it re-absorbs the CO2 that was driven off it when the original limestone was burnt – in effect it turns back into limestone.
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