The order in which salt and polyelectrolyte is added to a solution influences the structure of adsorbed layers on surfaces in contact with the solution and the interactions between surfaces across such solutions. By performing surface force measurements, it is shown that the strong attraction observed between polyelectrolyte coated surfaces in low ionic strength solutions is changed into a long ranged repulsion at solution of high ionic strength. This repulsion is more long ranged and larger in magnitude when the salt is added before the polyelectrolyte than when additions are done in the reverse order. When increasing the ionic strength in steps, the layer thickness and short range repulsion increases. We suggest that this is due to an increased adsorption of the polyelectrolyte. Mean field calculations (Scheutjens-Fleer model) were used to rationalize experimental findings. The results show that the adsorbed layer is much more extended in high ionic strength solutions. Furthermore, we show that the adsorption of polyelectrolyte is increased with ionic strength when the non-electrostatic interaction between polymer segments and the solvent is unfavourable.