Smooth out very rough cement walls?


My house has some very rough cement walls that I would like to smoothen out. They are pained with varying layers of paint. Might be hard to tell from the picture, but they are rough to the point where you can easily hurt yourself if you scrub your arm on it.

I'm really not experienced with DIY, but would like to do this as a project this spring/summer. The rooms don't have to be liveable for a good while.

I think i will definitely need to get a sander and smooth them down before painting them? If someone could lay out the basic steps for me that would be great and I'll do my research from there. (Sorry I would google it myself but it's very hard to google DIY stuff as I'm not English so I don't really know the terminology!)

q smooth out very rough cement walls
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