the invention of a gravity inversion field is well overdue

I'm painting the bathroom ceiling. Or rather, I'm preparing to paint the bathroom ceiling.
Plan
Monday: sand and wash ceiling
Tuesday: undercoat ceiling
Wednesday-Thursday: paint ceiling
Friday: Tidy up

Reality
Monday: hand sand and wash, informed by dad I'll have to use the electric sander and a paint scraper because the current condition is so poor it won't take a new coat, sanded some and scraped off 1m square
Tuesday: sanding off areas that wont scrape and scraping as the sander hits loose areas - about 1 square foot done by lunch time....I might have it all cleaned by the end of the week. I have to keep stopping and doing other things to rest my aching arms.

Friday Update
Still sanding/scraping the ceiling - in some areas the sander works, in others it doesn't. In some areas I can scrape off swathes, in most areas its bits less than a cm 2. I'm also going through the paint in some areas and tearing off cardboard. Day 1 (Monday) had the most success. Tuesday and Thursday was sheer torture. Wednesday I did a lot of other things. Today seems to be more of the scrape off large sections again. If I can get all the loose stuff off today, I've tested a fine sandpaper which seems to smooth all the different types of surface and maybe I can undercoat tomorrow...but I'm thinking it will be closer to Monday. I do have to get it done by then though, or I'll be off on a plane with it half finished.