hi,fellas,i'm doing up my flat it's from the late 60's & the whole building is pure solid rock hard concrete. except in 2 of the rooms,where i think theres been some serious movement or serious leeking over the years & the concrete ceilings have blown in places & big chunks have come away. you can see all the steel rods in the concrete ceiling are rusty & flaky as fcuk. theres also s**t loads of pebbles in the concrete ceiling? what would be the best way to restore complete order with this ceiling?