second and third tank 12 and 13 are connected to a second pump 22 by means of conduits 17 18 and 19 the water and solid ingredients are alternately mixed and pumped from tanks 12 and 13 to insure continuous flow a valve not shown is attached to the junction of conduits 17 18 and 19 to direct flow from either tank 12 or 13 the pumps 21 and 22 transport the acid and the slurry through separate hose lengths 23 and 24 to a y section 32 which is the inlet to a passive mixer 30 motor 40 which is used to power pumps 21 and 22 may also be mounted on support platform 10 referring to fig2 the passive mixer 30 is shown with hose lines 23 and 24 connected thereto controlled quantities of acid and slurry are pumped through lines 23 and 24 respectively within the passive mixer 30 is a spiral nozzle section 31 responsible for all the mixing which takes place between the acid and the slurry thereafter the acid slurry mixture is discharged from the passive mixer 30 and allowed to foam and set without the addition of heat other than that which it generates itself in the preferred embodiment the water added to tank 12 and 13 is at a temperature of 70 u00b0 f to 90 u00b0 f 21 u00b0 c to 32 u00b0 c the pumps 21 and 22 and hose lines 23 and 24 are sized to accommodate acid and slurry mass flow rates in which the slurry 39 s mass flow rate is about four times that of the acid 39 s mass flow rate when prepared under the conditions as set forth above the product will set in approximately 2 minutes while in accordance with the.