Joint compound is a white substance similar to plaster

Plaster

Plaster is a building material used for coating walls and ceilings. Plaster starts as a dry powder similar to mortar or cement and like those materials it is mixed with water to form a paste which liberates heat and then hardens. Unlike mortar and cement, plaster remains quite soft after setting,...

 used to seal joints between sheets of drywall

Drywall

Drywall, also known as plasterboard, wallboard or gypsum board is a panel made of gypsum plaster pressed between two thick sheets of paper...

, primarily in building construction. It is often referred to simply as mud.

Ready-mix lightweight joint compound

Ready-mix lightweight joint compound is a pre-made form of joint compound designed for fast application and easy maintenance. The compound is a complex combination of water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

, limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

, expanded perlite

Perlite

Perlite is an amorphous volcanic glass that has a relatively high water content, typically formed by the hydration of obsidian. It occurs naturally and has the unusual property of greatly expanding when heated sufficiently...

, ethylene-vinyl acetate

Acetate

An acetate is a derivative of acetic acid. This term includes salts and esters, as well as the anion found in solution. Most of the approximately 5 billion kilograms of acetic acid produced annually in industry are used in the production of acetates, which usually take the form of polymers. In...

 polymer

Polymer

A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

 and attapulgite. This delicate mixture of compounds gives it a very creamy texture which allows it to spread onto surface with great ease.

Usage

Ready-mixed joint compound is most commonly used in hanging drywall

Drywall

Drywall, also known as plasterboard, wallboard or gypsum board is a panel made of gypsum plaster pressed between two thick sheets of paper...

 for new or remodeled homes. Application is simple and easy, usually never taking more than three or four coats. When used for new walls, joint compound effectively eliminates all blemishes from the surface of the drywall, such as drilled in screws, hanging tape, or drywall tape. Joint compound can be used to finish gypsum

Gypsum

Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...

 panel joints, corner bead, trim and fasteners, as well as skim coating. In addition, it is also very handy for fixing minor blemishes or damages to walls. It easily patches up holes, bumps, tears, and other minor damages.

Ready-mix joint compound is usually more forgiving than the traditional form of joint compound. It can be used for as long of a period of time as needed, and does not dry up unless left unattended for a long period of time. Traditional "mix-it-yourself" joint compound usually lasts for one to two hours before drying. However, if it happens to set for more than a few hours, then you will need to apply water very liberally as needed to retain its soft texture.

Often referred to as drywall taping mud, joint compound is the primary material used in the drywall industry by a tradesperson, or applicator, called a "taper" or "drywall taper." A similar compound is used in various ways as a sprayed-on textural finishing for gypsum panel walls and ceilings that have been pre-sealed and coated with joint compound. The flexibility and plastic qualities of joint compound make it a very versatile material both as sealer or finishing coat for wall surfaces, and also in decorative applications that range from machine sprayed texturing to hand-trowelled or even hand-crafted and sculptural finishes. In North America the application of joint mud and drywall tape sealer and trowelled joint compound on gypsum panels is a standard construction technique for painted wall and ceiling surfaces. Until more recently in North America, and through the world, several different plasters such as veneer plaster and "plaster of paris" have been used in a similar ways to joint compounds as fillers or for decorative purposes since ancient times, and the actual make up and working properties of these compounds is much similar. Modern ready-mixes or powder and water mixes are available in a wide range of styles from slow-drying to quick-drying to suit specific demands for use by contractors or decorators.

While joint compounds are used for bedding tape and initial layers overtop, it is best to apply topping compound for finish layer(s) that level and sand more evenly. Both require thinning for practical application.

Health concerns

Joint compound mixes manufactured prior to the 1980s often contained a complex mixture of several substances. Among the additives used were asbestos

Asbestos

Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. They all have in common their eponymous, asbestiform habit: long, thin fibrous crystals...

fibers, which provided cohesiveness. Exposure to fibral asbestos has been linked to various health conditions, including cancer in some instances. Joint compounds manufactured from 1980 onward were required to have asbestos removed in favor of other compounds due to legislation to ban asbestos' widespread use.