If you want to go further on rust effects
Apply the wash using a medium sized round soft paintbrush. Deposit the wash on to your scale model around details, seams and in holes creating fake shadows hi-lighting details. Let the wash dry for about 15 minutes then clean the excess using a brush dampened with Thinner for Washes. Use a fine pointy 00 size brush to apply more refined pin-washes where you feel they might be necessary such as in weld seams and around bolts and rivets.