A surface application unit for applying a surface application substance to all or a portion of a surface of a planar substrate in a machine for printing planar substrates. The unit includes an applicator roller (11) which is rotated (T) and can be positioned against all or a portion of the surface of the substrate in order to apply the substance thereto; an anilox roller (13) which is rotated (S) and positioned against the applicator roller (11) and which covers the applicator roller (11) with the substance; and a supply system (14) which supplies the anilox roller (13) with the substance and which is provided with a substance tank, a pump, a device for circulating the substance, and a device (16) which is held against the anilox roller (13) in order to supply the substance to the roller. A recovery system (18) mounted downstream of the applicator roller (11) can be positioned against the applicator roller (11) to recover excess substance on the roller (11).