Hi niennari :: with respect to water and humidity, one on the roof and the other on the walls, they are a theme that looks like the "RENCOR", sooner or later it appears and bothers a lot, on a roof of more than 50 years, there are so many cracks, and fissures to make a filter, so waterproofing it is a job that if it is not well done, it is more useless than a deaf ear, to start, it must be cleaned well, by steel brush, scraper, chip floor and everything else, until leaving the material in sight. Then with a waterproofing, (a very good one is the "TACURU"), diluted with water, give 2 or 3 hands allowing it to absorb well in the fissures, then undiluted, others, and just put a good, thick membrane on top. new. not aged in the tank, work done by a good setter, then even if a sink is made on the roof, you do not find out, if instead, you add cementitious material on the old, no matter how, it will rain more on the hot days of Sun, that cold from heavy rain. good luck with that.