Technical Focus: Dispelling myths about poured gypsum floors

Gypsum is a mineral that has been used in building materials for centuries. However, gypsum concrete as an underlayment is still misunderstood despite its growth in popularity over the last 40 years. As a result, several myths about using gypsum in this way have become canonized. This article aims to expose these myths and provide information about the benefits of using gypsum-based concrete underlayments.

Gypsum is a mineral of crystalline structure composed of calcium, sulfate and two molecules of water (CaSO4-2H2O, also known as calcium sulfate dihydrate). It is a very common mineral found around the world — right behind its more plentiful cousin, limestone (calcium carbonate). The process of cooking gypsum is known as “calcination.” During this process, 75% of the water is removed from the mineral, leaving calcium sulfate hemihydrate. This process is reversible. When water is added to calcium sulfate hemihydrate, hydration begins and crystal growth occurs, returning it to its original mineral form — gypsum. It is this process that allows gypsum to offer characteristics other binders cannot.