My house flooded and I had the first 4 feet of drywall replaced. It was taped/floated and texturized. Once the paint started going on, I noticed a faint dark line in the middle. It doesn't seem to be the tape itself and I'm thinking it may be the mud. The paint used was BEHR's with primer and paint in one. The contractor sanded down the area to re-texturize as the texture was not blended well to match but one some of the walls the line seems to reappear. From what I am reading, this could be because I need a coat of true primer on the wall and the line could be the absorption of the mud being different than the rest of the wall. I've also read where skim coating the walls may help with this. I have attached a picture but it may not show up. I am concerned about it because it is very visibly noticeable when you walk in a room and its in a few of them. Anyone familiar with this, know what can cause this and how to properly remediate? [ATTACH]86148[/ATTACH] Thanks in advance!

had ugly 70's paneling on walls......someone slapped wallpaper over that and painted. Under that is 1/2 drywall. I took some of the paneling off since it was easier to just rip it out- Now I am left with a room with 1/2 drywall (unfinished since panels covered it)- Rather than rip that all down- was thinking of screwing 1/4" drywall over it- This seem like an OK approach or am I missing something that may make this more work in the end......