I only ever apply Silicon to a dry joint, never skirting over grouted joint. When applying Silicon into a dry joint, if the nozzle is cut just bigger than the joint width upon gentle application, you will get to see the excess Silicon start to gently ooze from that point, keep going applying gentle equal pressure until you have got to the end of the run. Spray with soapy water...lashings of it and then use wet finger to remove. Any Silicon that has squeezed up into a vertical joint can then be pushed back beyond the surface of the tile with a nail. Grout down the vertical joints after the Silicon has cured....job done.....Gaz