Abstract: A method of coating a substrate surface, which method comprises: (a) applying a primer composition to the substrate surface which primer composition comprises thermoplastic polymer material dispersed in an inert liquid diluent, at least 50% by weight of said theroplastic polymeric material being constituted by at least one thermoplastic aromatic polyethersulphone; (b) before the applied primer composition has become touch-dry, applying a dispersion of a tetrafluoroethylene polymer top-coat material in an inert liquid diluent over the coated substrate; and (c) removing the inert liquid diluent or diluents and sintering the combined coating of the primer and top-coat layers. The primer compositions do not in the claimed method, need to be dried and baked to exert an effective priming action.