Have you heard the one about the Great Wall of China being built out of rice? I know, it sounds like a joke about a Chinese takeaway. But it turns out to be true.
Scientists at Zhejiang University in China have found that the lime mortar between the stone blocks was mixed with sticky rice, and this helps account for the Great Wall’s strength and stability, including its ability to withstand earthquakes.
This got me thinking about the other ingredients of vegetable and animal origin that have been used in building materials over the years.
Old paints were often made with milk, and this is even making a comeback. Lime, milk, and natural pigments are all you need to create a beautiful matt finish on walls and timbers. And whilst it looks soft and chalky, the casein in the milk ensures that the paint won’t flake or peel.
Traditional distemper was made with rabbit-skin glue, which made it set hard on the wall. It order to keep the distemper from setting in the pots, they were kept floating in buckets of hot water – which is why we still refer to them as paint kettles.
Milk-derived casein also plays a part in the adhesives used in wood laminates and some types of plywood. And other traditional wood glues were made by boiling down animal bones.
It is also said that the colour of the traditional pink limewash on East Anglian houses came from the animal blood that was added to it. The blood acted as a plasticiser, and also allegedly made the limewash water-repellent.
The lime plaster that still remains in thousands of our old buildings was usually reinforced with horsehair, to control cracking. I used some recently in a repair job on a listed building, and was pleased to find that I didn’t first have to creep up on a horse and snip off its tail – you can buy bundles of hair in handy 50mm lengths from paintbrush manufacturers.
You might have heard of recent experiments to build houses out of hay bales. But straw has been used as an insulation material for centuries. In fact, until quite recently straw was the only insulation material available to builders. It was used to line roofs and ceilings, and was even fixed to the outsides of solid masonry walls and plastered over, as a clever medieval forerunner of the external insulation techniques that are now claimed to be the “latest thing”.
There is also evidence that animal dung was used as a binder in the “daub” part of wattle-and-daub – the traditional infill material in old timber-framed buildings.
So while we might think of most building materials as being “man made”, we should remember the part played in them, traditionally and today, by animal and vegetable products.
