Abstract: Stacks of paper sheets are transported at a level above a heated paste tank and their lower edge faces are contacted by the upper portion of the peripheral surface of a driven wheel-shaped applicator whose lower portion dips into the supply of paste in the tank and an intermediate portion of which is located above the upper level of the supply of paste and upstream of the upper portion. The intermediate portion of the peripheral surface receives a mixture of paste and air from a spray nozzle which, in turn, receives the mixture from a conduit containing a mixer and a pump and having an intake end immersed in the supply of paste in the tank. The pump draws air or another gas into the conduit by way of a pipe upstream of the mixer, and the latter converts the supplied paste and gaseous fluid into a foam which is delivered to the orifice of the nozzle.