A slurry mixing system calculates a density of a slurry using measured pressure differential and based on a bulk velocity of the slurry. Slurry from mixing of dry blend and mix fluid enters a one or more tanks having agitators. A pump then pumps the slurry from the tank(s) to the well, and a portion of the slurry is recirculating back to a mixer. From the recirculated path, a direct slurry weight sensor measures a pressure differential of the slurry between two vertical measurement points of a known volume. The sensor can measure a velocity of the recirculated slurry, or the recirculated slurry can be maintained at a velocity. Based on these measures, the controller calculates a density of the slurry, monitors a ratio of the dry blend and the mix fluid, and adjusts the ratio based on the calculated density of the slurry if there is a discrepancy.

The invention relates to an apparatus and a method for production of additives enhancing water tightness of structural and binding building materials. The method comprises the steps of: preparing a hydrophobing agent by esterifying 60-80 m % of vegetable oil by a mixture consisting of 20-40 m % ethyl alcohol and 0.1-5 m % of methyl alcohol of the whole mass of the agent, then adding 5-30 m % agent by spraying through nozzles and water to a body of burnt lime in a reactor, and prior to adding the agent and water a mixture of 2-8 m % ethyl alcohol and 0.1-1 m % of methyl alcohol of the whole mass of the body of burnt lime is added by spraying through nozzles, while the mixture is agitating mechanically till a homogeneous mixture is prepared, then adding 40-65 m % water to the mixture, and ceasing mechanical agitating after commencement of the fierce chemical reaction.