How Does Joint Compound Work?

1. Joint compound, or dry wall mud, is used in every home and business project of the modern building age. At one point in time, it came in large sacks of dry powder, and the professional had to add the proper water amount for the mix to be consistent. Today, you can purchase premix versions in small containers or large 5-gallon plastic buckets. Joint compound now comes in three coatings: rough coat, medium coat and the top finish.
2. The rough coat joint compound is a heavy paste-like mix that in some cases may even have a form of adhesive in the premix. This type of dry wall mud should never have any water added to the mixture, as the consistency is made for the first coat of filling holes and adhering paper tape for covering joints. When applying this first coat of compound to drywall, care should be taken so as not to leave any large ridges or thick joints that have to be removed when dry. The amount of sanding required to dress down any thick application can be extremely laborious.
3. Some professionals may thin down the first coat, or rough coat, compound with water for the second application. Too much water could adversely affect the adhesion of the compound. Too much water could also cause the paper covering of the drywall to separate from the gypsum material. The medium coat is used to fill in any shrinkage gaps that will occur for nail holes and the corner joint bead. Fluid motion should be used when applying the medium coat, as you will want to begin to feather the edges and create a smooth and level blend from the compound onto the drywall.
4. The finish topcoat is a special blend of smaller particles for the joint compound. The rough coat will have large particles of gypsum for the grab or adhesion to the dry wall board. The topcoat material will have the finest blend of gypsum of almost a talcum like powder in the dry form. Pigment may also be added to the finish coat mixture for the primer of the paint. This pigment addition helps in the reduction of the amount of paint used on a new dry wall. As the dried joint compound will absorb a lot of paint before the pores are sealed.
5. Most texture placed on walls and ceilings are nothing more than the finish coat of joint compound mixed with any color latex paint. This combination is mixed well in a plastic container and applied to the wall or ceiling surface with a coarse brush or thick napped roller. Second coating of paint can be achieved by paint only and using the same thick napped roller or large brush so all crevices are completely filled with paint.

Resources

• More Information on Joint Compounds and Finishes of Walls