A skim coat of joint compound is intended to
conceal small imperfections in joints and on the surface of the
gypsum board, smooth the texture of the paper, minimize
differences in surface porosity, and create a more uniform
surface to which the final decoration can be applied.
A "skim coat" is essentially a "film" of joint compound and is
not a readily measurable thickness. There is no specific mil
thickness that constitutes a proper skim coat. A skim coat is
described in the foregoing text as being "trowel applied" with
the intent being that the consistency (viscosity) of the joint
compound be such that it can be applied by a trowel. Other
tools may be used for application so long as the trowel
consistency is achieved.