Renovations: Master Bedroom #2

Having got the cupboards out of the way it was time to tackle the painting.
I like to work in a top down fashion. Do the ceilings then the walls and finally the room trim including window frames, skirting boards etc.
First task is to strip out what I can, light fixtures, picture hooks and other crap left by previous occupants. Then patch the holes this leaves behind plus fix any other defects. After that it is supposedly a simple task of cleaning walls and ceiling and then re-painting. If only.
I had been aware of some flaking paint on the ceiling, so I did an experiment of sanding and repainting a small patch. It improved the look, but I had doubts about the longevity of this solution. So I did a further experiment and used a scraper on the flakes. I soon found that I could scrape off a fair bit of ceiling paint. It was only loosely bonded to the drywall above. I began to think about two things, firstly why was it doing this and secondly how was I going to fix it.
My first thought on the why was moisture or water. The bathroom and kitchen both have much more serious paint flaking. Water from below was not an option for the bedroom, whereas it could be for the bathroom and kitchen. So next step was a trip into the roof crawl space to see if there was evidence of water. My gutters had been blocked and overflowing, maybe it had come into the roof.
Gratifyingly the roof space was dry and showed no evidence of water penetration.
So i had a closer look at the paint that I had scraped off. The first thing that occured to me was that the paint was coming off the paper covering the drywall. Basically it had only bonded lightly to the ceiling. Also there were patterns, a lot of the flaking was near to joints in the drywall.
I will never know, but I suspect that the ceiling was never primed or undercoated properly. Possibly it was a bad mix of paints, possibly the jointing compound between the drywall sheets had not set properly, possibly moisture is coming through the join. Whatever, I scraped and sanded off what I could, but I think that the problem will re-occur.
But this gave me a problem. Painting over the cleaned area would leave a noticeable ridge line. I had no idea how to overcome this.
Google is my friend. I quickly discovered that I needed to skim coat the ceiling, or at least the parts that I had exposed. This involves spreading a thin layer of jointing compound on the ceiling to even it out. Oh dear, the Bludger is expected to do this? You expect me to spread a thin coat of stuff on a ceiling so that it does not fall off neither that it is too thick nor too thin? Warning impending ceiling disaster.
I dutifully headed off to my regular hardware store to purchase the items that I would need. I felt vaguely uneasy about this however. Had I taken enough of the loose material off? Are there other patches that will fail inside a year or two, and I will need to repeat the exercise? Can I even do it?
{note: Posting a half completed blog from 3 years ago}