A wallboard joint compound includes a base joint compound having a homogeneous, paste-like blend of water and at least one of a filler, a binder, a thickener, a suspending agent, a biocide, a preservative, a mineral filler and expanded perlite; and an additive discretely added to the base joint compound to be available for use once mixed into the base joint compound just prior to application of the wallboard joint compound by a user.