We are currently doing up a rental property in return for cheap rent with option to buy. The interior paint is cracked and peeling in many places. The paint that peels off is 1.5 mm thick. What is the best way of preparing the walls for painting? How much should we scrape off? I'm worried that if we don't scrape enough off then the paint will only peel or crack again... but to scrape all off is a massive job... Really have no idea what to do so any help would be much appreciated. Thank you.

With that thickness of paint, some of it is probably lead-based. Be sure to take appropriate precautions, especially if you have small children.

In terms of the wall, you definitely need to remove all loose and peeling paint. With such thick divots, you will probably have to fill them with joint compound.

We bought an 85 year old home for a great price, although we experienced similar problems that you describe. Room by room we covered the peeling and deteriorating plaster/lath wall with new drywall. If you are considering buying this home, you might want to calculate the covering of the wall in lieu of the time and hazards involved with scraping/sanding. Depending on the amount of peeling, look into wallpaper as well. Good Luck!