A device and a process for the continuous application of a refractory slurry to a surface incorporate a batch reactor (10) for the controlled mixing of the slurry, a product vessel (60) in communication with the batch reactor (10) to contain the mixed slurry, and a variable-rate spraying applicator or nozzle in communication with the product vessel and with an air supply. A controller (100) controls input to, output from, and the operation of, the batch mixer (10), and monitors batch production. The controller (100) monitors the amount of slurry contained in the product vessel (60). If the level of slurry in the product hopper is such that the product hopper cannot accommodate an additional batch of slurry, the controller interrupts batch production and resumes production when the product hopper can accept the contents of the batch reactor (10).