Joint compound is a decorative material used to smooth out wall surfaces, a thick paste-like paint that is an essential product before painting. It is applied over primer or directly onto the object to fill in uneven defects on the surface to be coated.

Made from a small amount of paint base, additives, a large quantity of filler, and an appropriate amount of coloring pigment, the main pigments used are iron red, carbon black, chrome yellow, etc. The fillers mainly include calcium carbonate and talc. It can fill in concave work surfaces and can also be applied over the entire surface after scraping. Typically, it is applied to the surface of the undercoat after the undercoat layer has dried. It requires good adhesion and no cracking during the baking process.