This study suggests a different route for the modification of flat/float glass surfaces; i.e. exchange of ionic species originating from in-line vapour deposition of salt as compared to the conventional route of immersing the glass in a molten salt bath. The aim of this work is to develop a more flexible and, eventually, more rapid process for improving the mechanical strength of flat glass by introducing external material into the surface. We discuss how chemical strengthening can be performed through the application of potassium chloride on the glass surface by vapour deposition, and in-line thermally activated ion exchange. The method presented here has the potential to be up-scaled and to be used in in-line production in the future, which would make it possible to produce large quantities of chemically strengthened flat glass at a considerably lower cost.