Some building materials that start with the letter "J" are jack studs and joint compound. Jack studs, which are also called trimmers, are used at both sides of a door, window or other fenestration. They help support the header, which is the heavier framing above the opening.
The header then supports the studs above it. The jack stud is smaller than the king stud and takes its name from a nickname for a common man.
Joint compound is a synthetic, premixed paste that's used with tape to hide the joints between panels of drywall. There are several types of joint compound. Setting compound is used for areas around electrical boxes and to smooth out cracks and the depressions caused by nails and screws. This type of joint compound dries quickly, usually within 45 minutes. It also comes in a variety that, unlike standard setting compound, is easy to sand.
Drying compound takes much longer to dry; one layer can take up to 24 hours. It is used at the joints between drywall panels and at corners to embed the tape. When the first coat dries, another coat is applied over the tape, and it's sanded smooth. Drying compound is lightweight and easy to sand. Topping compound is then added and also sanded after it dries.