A Can of Worms

Yes, a can of worms is a nice way of saying what this situation really is. My sister described it a bit more concisely as "a major mo fo".

I am painting Ethan's room and this is his window sill, which has been messed up for a long time. I thought that the paint failure was due to the very hard use it was getting from the teenager, with spilt water and whatnot. Turns out I was wrong.

Further investigation reveals that the paint did not adhere on any of the mud joints in the entire room. No wonder the paint dinged so easily.

It literally peals off in these nice, easy strips. Kind of reminds me of waxing my legs, tbh.

I'm using one of these for the task.

These are my thoughts...

I'm pretty sure that it is the primer that failed. I think the primer didn't adhere because the mud was not given enough time to cure before being coated (because the adhesion is better on the plain drywall). This adhesion issue would/could also be confounded by walls that weren't properly dusted down prior to primer and/or a poor quality primer. Remember, I had problems with adhesion when painting the boys' bathroom. 

Good lord, please don't have the paint job blow like this in the entire house, I won't be able to take it.