We propose an adaptation of the osmotic stress technique for determining equations of state of colloids covered by polymer films. We describe here the case of silica particles covered by 6 or 7 layers of polyelectrolyte multilayers. The establishment of a pressure-distance curve allows the interpretation of colloidal interactions over more than four orders of magnitude in pressure. This large range allows a clear separation between three distinct regimes: layer compression, brush extension and at very low pressures a regime of weak repulsion. The physical origins of the regimes are discussed and described by models of colloidal interactions.