A simple model for an incommensurate dense metal layer adsorbed on a metal substrate is presented, in which both metals are represented as jellium with pseudopotentials. It is first shown that a single lattice plane detached from the bulk metal tends to contract, because the electrostatic attraction from the neighboring planes is missing. When the monolayer is brought in contact with the adsorbate the lattice constant expands again, but is still shorter than for a bulk metal.