On 14/05/2020 13:18, R D S wrote:
We're moving some stuff around at work, and there's patches of paint
need touching up.

Someone i'm guessing has painted fresh plaster and not prepared the wall
first,

So while the paint looks OK as it stands, where we are painting, it is
as if the new paint is wetting the old stuff and then the whole lot
wants to come off the wall!

So we scraped the loose off, sized the parts that look like bare
plaster, but as we go back and paint more of the same is happening.

So whats the solution here? It's looking like all the existing paint
needs to come off, the best way of doing this appears to be put ####ing
new paint on it!

Sand it all off?
I had a similar problem painting a modern extension. No idea what caused
it (maybe the (crap!) plasterer over-polished the plaster) but the
solution was to spray the problem areas with stain stop and then paint
them normally.