I am renovating my son's bedroom and trying to make the walls as nice as is reasonable before repainting. There are a few cracks like this in the paint. It looks like on top of the drywall there is paint, wallpaper, and then a few more layers of paint. The cracks could be at the seams of the drywall from expansion and contraction. They could be at the seams of the wallpaper. They could be something else. Most of the cracks come straightish down below the sides of windows, which makes me think drywall seams.
I gouged out one crack and filled it with joint compound to see how that works. Since the drywall is old, it was really hard to tell if this is at a drywall seam or not - there are places where previous work, maybe mouse damage, and who knows what else has made the drywall crumble from behind. These are the joys of an older house!
How would you handle this?
Are the cracks just in the paint, or do they go all the way through to the drywall beneath?
Drywall joint compound has no flex. These cracks were caused by the wall moving via some means. Either thermal expansion and contraction, the house settling, or some other construction putting torsion on it. Therefore, if you fill it with joint compound it'll just crack again. The "correct" method I suppose is to notch it out and make a joint over it with seam tape and joint compound, then sand it flat, touch it up, sand it flat again, etc.
Here in reality, though, I had several of these in the walls in my house (particularly in the corners) and I just filled them in with painter's caulk -- which does flex. Screw it. It's getting painted over anyway. I've had no issues, and I probably avoided taking years off my life not only in aggravation but also in not breathing yet more drywall dust.