Walls and Ceilings - Family room makeover,how to fix bad mud job

I am trying to make our family roon more livable, I am starting with the walls. The previous owners did the dry walling and mudding. It appears he only put one or two coats of mud on. When you look at the seams there are gullies where the tape is and ridges on the outside where he did not sand properly. Here is my problem. He painted over his poor work. How can I fix this and re mud the seams the right way. Thank you!

Even though the mud is under paint, it can be sanded. Even though there is paint on the wall, mud can still be applied.

100 grit paper will sand right through the paint.

Hope this helps.

I'd say forego the sanding for now. unless you are using a palm sander it will take forever. You will have to put mud over the joints. I'm guessing the butt joints wont be too bad but the bands(horizontal seams) are going to take some work. Put your 12" knife or a straight edge against the wall to see how bad of a hump there is. Put mud on either side of this hump until flat. Fill in any voids with mud. Don't forget the corners.