Ready, SET, Science

How Plaster Works

Just call us Bill Nye, the Plaster Guy…

After last week’s blog on the history of plaster, we figured we’d continue and talk about what plaster actually is. There’s a handful of different types of plaster, but they are all generally made in the same way: by mixing dry powder with water to make a strong yet workable material. The three most common types of plaster are lime, gypsum, and cement, SET plaster is a cementitious plaster aka made of cement.

The setting of plaster occurs through a chemical reaction known as hydration. When water is added to plaster, it triggers the hydration of the calcium sulfate hemihydrate particles. These particles dissolve in water and then re-crystallize as calcium sulfate dihydrate, which forms a network of interlocking crystals that harden and set over time.

The setting time of plaster can be controlled by adjusting the liquid-to-plaster ratio, as well as the temperature and humidity of the surrounding environment. Too much liquid can result in a weaker plaster, while too little liquid may lead to incomplete hydration. The rate of hardening can also be influenced by additives, which can either accelerate or slow down the hydration process.

One of the many qualities that makes plaster an ideal building material is its fire resistance. Gypsum, one of the main ingredients of plaster, is a natural fire-resistant material that does not burn. Plaster is also known for its excellent thermal insulation properties, which helps regulate temperature and reduce energy consumption in buildings.

Plaster is also extremely durable and can last for many years with proper care and maintenance. It is resistant to wear and tear, cracking, and decay, making it a durable and long-lasting building material.