A system that allows a gel to be formed by mixing the solid precursor of the gel and water and spraying same onto surfaces is provided. The system includes: a conveyor for the added gelling agent or solid; a pair of openings on the sides of the conveyor tube; a dosing device located after the openings, which distributes the amount of solid added to the conveyor; a Venturi shut-off valve; a mains connection which allows water to enter the system when the water shut-off valve is opened; a Venturi inlet pipe which connects to the Venturi chamber through which the water passes; a Venturi outlet pipe through which the water passes with the solid; and a lance for discharging the gel produced by mixing the water and the solid.