Abstract: An apparatus and associated method for conditioning or reconditioning oil well drilling mud, comprising multiple hoppers for holding dry additive. Each hopper has a mechanism permitting the additive to be fed into an entrainment chamber at controlled, pre-selected rates. The additives are thus mixed at controlled rates with a free jet of mud forced across the entrainment chamber, to quickly achieve the desired density, viscosity and other properties of the mud. An augur is used to force the dry additive through an adjustable gate valve to control the additive flow rate. Or, the augur may be rotated at selected rates, and a fixed area additive flow passage employed between the hopper and the entrainment chamber.