This is a very different blog post from previous posts on the subject of working with different types of lime. By lime I mean the building material. This series of blogs will detail my experiences good and bad of working with it. Lime has a reputation of being an eco-friendly building material and this is semi-true, certainly compared to concrete. But it also has a number of features that make it not just attractive as a building material but vital in certain instances. The most important of these are that it breathes. When used in dwellings this makes a huge difference to levels of damp – and this is one reason why I have used it for two specialist insulation projects.
But first a little chemical background (see figure below). If you heat limestone to about 900 degrees C the carbon dioxide is driven out in a chemical reaction leaving calcium oxide (known as quicklime). The lime is then “slaked”. That is water is added. This violent reaction liberates a lot of heat forming calcium hydroxide. This is what we call lime and is the basis of lime products. In the presence of carbon dioxide the calcium hydroxide slowly changes back to limestone forming a hard mortar or other lime variant. To slightly complicate things there is a from of lime called hydraulic lime which will set under water, this contains clay impurities and requires water to set. The other forms I have worked with and will describe will gradually set in the air. Of course you do not use lime alone but mix it with other things such as sand or dyes.
I have worked with a number of different types of lime product. Lime mortar to re-point a stone wall, “course stuff” a sort of lime plaster used internally as a surface to put other things on, hydraulic lime and limewash which is a breathable alternative to paint. I will describe these and how I have used them in more detail in future posts.