Apparatus for protecting the surface of freshly printed sheets which are deposited upon one another to form a sheet pile includes an applicator for applying to the respective sheets a separating-agent layer formed of solid particles of separating agent, the layer of separating agent being formed of a mixture including at least one degradable separating agent substance, an aqueous vehicle liquid, and at least one mixture component which degrades the separating agent substance upon simultaneous contact with the separating agent substance and the vehicle liquid.