Drywall Joint Compound

Also known as 'mud', is used to seal joints between sheets of drywall. It is usually a mixture of water and gypsum dust or other binding ingredients. It serves two purposes: to create a bond between sheets of drywall to strengthen the structure of your house, and to create a seamless appearance between sheets of drywall. Drywall mud is now available in a non-toxic, zero-VOC formulation (no Volatile Organic Compounds).

Drywall compounds will have different purposes depending on the 'coat'. The first coat is typically meant to fill the joints and create a solid bond between sheets of drywall so that cracks will not appear as the house shifts over time. This initial coat will cure to be very hard and is not meant to be sanded. It is usually sold as a powder and must be mixed with water. The second and third coats are meant to create a smooth surface and are meant to be sanded smooth. It is usually sold as a 'mud' that doesn't need to be mixed with water.

Most modern drywall joint compounds contain a mixture of ingredients including limestone, talc and small amounts of crystalline silica, which can be toxic if inhaled in large concentrations. Drywall compound needs to be sanded and the ingredients will become airborne so be sure to clean frequently and wear a dust mask or respirator that has been properly sized to fit your head and face. Some manufacturers are producing hypo-allergenic or non-toxic drywall compounds that are designed to be less agitating when sanded. These are also typically VOC-free.

Drywall was invented in 1916, but didn't catch on until the baby boom in the 1940's and 1950's, when a lot of new homes were built to accommodate all of the new babies! Gypsum drywall was cheap, lightweight and easy to install compared to plaster.