The mud used here must adhere well and be firm, and is referred to as a taping compound; a filler coat, which covers and roughly smoothes the tape; and a finish coat, or topping coat, which is extremely smooth. A topping compound is soft, smooth, and sandable. The three main types of compounds used in drywall repair are joint sealing compounds, patching compounds, and wallpaper paste. Joint sealing compounds are used to fill the voids between two adjoining boards and create a water-resistant seal. They also help reduce noise when you move furniture. Joint sealing compounds come in several colors: white, gray, black, and red. These products are easy to use and usually contain some type of plasticizer to make them softer. Patching compounds are used to cover damaged areas of drywall and restore the wall to its original condition. There are two types of patching compounds: drywall mud and plaster. Drywall mud is a mixture of clay and starch; it can be mixed on site with water and sand to form a thin but solid coating that fills small holes and cracks in the wall and prevents moisture from entering the wall cavity. It's available in various colors, including white, so it can match existing paint where needed. Plaster is a word used for any of several materials used to fill large cavities in walls or ceilings, such as those left by old paintings or photographs.