Home Work

Remember school chemistry? Heat some limesone rock in a tube; bubble the gas that is given off through a test solution, to show that it is carbon dioxide. Let the heated rock cool down and it crumbles into a powder. This is 'quick lime' - 'quick' in the same sense as used in the old prayer book communion creed: "the quick and the dead"; quick meaning 'living' , 'lively'. Quick lime is Calcium Oxide and it is highly reactive, likely to burn you if you touch it

The next step in the school lab was to add water to the cooled quick lime - this creates a violent reaction and the test tube gets hot. The result is 'slaked lime', just like a slaked thirst - water has been added. Slaked lime is Calcium Hydroxide, a compound of Calcium, Hydrogen and Oxygen. This chemical process is what was carried out on an industrial scale in the lime kilns that are found all over the country, now disused. The alkali Calcium Hydroxide was used for neutralising acid soils to increase production, or to create lime mortar, plaster and render

Today, I took my bucket of Calcium Hydroxide in water - in other words 'limewash' - and brushed as thin a coat as possible on to the lime-render walls. The water is rapidly absorbed by the render (too rapidly unless I diligently dampen the walls before I brush on the limewash, making it difficult to spread thinly). This leaves a thin coating of solid Calcium Hydroxide on the wall

Now more chemistry happens. Over the course of a day or two, the Calcium Hydroxide reacts with Carbon Dioxide in the air, producing Calcium Carbonate (Calcium, Carbon and Oxygen chemically combined), in the form of the mineral Calcite. The reaction also gives off some water vapour. Here is the scary chemical equation:

Ca(OH)2 (aq) + CO2 (g) → CaCO3 (s) + H2O

Calcite is a stable, protective coating for the wall. It also has magical optical properties - refracting light in a way that creates a glorious and very satisfying lustre. It can even fluoresce a little as the daylight fades. Calcite is also the mineral that is present in limestone, so our chemistry has gone full circle

So, while many people were getting exasperated by another grey, damp day, I was relishing the perfect conditions to keep the walls damp and make it relatively easy to brush an even coat. The forecast is sunny and warm - perfect for driving on that chemistry. Rock solid