Clay is one of the oldest building materials on Earth, among other ancient, naturally-occurring geologic materials such as stone and organic materials like wood. Between one-half and two-thirds of the world’s population, in both traditional societies as well as developed countries, still live or work in buildings made with clay, often baked into brick, as an essential part of its load-bearing structure.
Many of the greatest mural paintings in Europe, like Michelangelo’s Sistine Chapel ceiling, are executed in fresco, meaning they are painted on a thin layer of wet plaster, called intonaco; the pigments sink into this layer so that the plaster itself becomes the medium holding them, which accounts for the excellent durability of fresco. Additional work may be added a secco on top of the dry plaster, though this is generally less durable.
Cement is a crucial component in buildings and roads — which is why some 80 percent of it is made and used in emerging economies. Cement plants account for 5 percent of global emissions of carbon dioxide, the main cause of global warming. Cement has no viable recycling potential; each new road, each new building needs new cement. Sixty percent of emissions caused by making cement are from the chemical reaction that makes it.