I've just had a lot of re-rendering and skimming work done in the hallway and lounge of my appartment. The plasterers have done a good job, but the main guy told me today that there are some tiny hairline cracks which keep appearing in the plaster. He reackons it's down to the age of the place (1935 building), and says they've tried to get rid of them but they keep appearing. In fairness, you can't really see them unless you look closely, but I'm just wondering if they will cover up with paint? He told me to use flexible paint designed for this type of surface. I've found some Dulux "flexi-paint" which says it will stop cracks appearing (and a similar product by Polyfilla). Is it worth using these or should I just use my normal matt ceiling paint? If I use this paint, should I still water down the first coats? Thanks for any helpful hints.