I live in a house that I believe was built in 1948. The basement walls are cinder block. I have areas of the walls that are stained and some areas that are crumbling. Some spots are bubbled and easy to push in. Not sure if it's the cinder block and/or the paint the previous owner used. When I moved in I was told there was a water problem in one corner and it had been waterproofed. I believe the waterproofing was done right because I don't really notice any new damage or worsening issues to the walls since I've been there. Most of the issues are in that corner but there are some other spotty areas. Most of the spotty areas seem to be confined to the base of the wall. My question is I want for now to just paint the walls to make it look nice. How do I go about preparing the wall to paint? Do I scrape as much of loose material off the wall as I can and then use some sort of sealer/paint? Any help would be greatly appreciated, Thanks.