Today my clawfoot was released from a 30 year imprisonment behind a cheesy DIY tub surround. Under the curled lip (top edge) there is weird rusty type bubbles. ??? odd. a bit of crumbling around faucet hole but, not rusty in appearance. The tub IS 103 years old (as is the house). I would like to mosaic tile around the outside of the tub for decorative purposes. I have only laid ceramic tile onto CBB counter tops and floors. Any idea how to prep the iron surface? Steel wool and oil? wire brush? no oil? Would oil create a barrier and interfere with mastic? should I use mastic? help, please.