Might be pva used by the plasterer. . I can't tell from the pics but we had areas that looked like splashes that didn't cover well with paint at all. The solution was to keep adding coats of paint!

I'm painting over our Valspar deep teal shade with a Valspar custom mix taken from a Hague Blue sample, which is a lot darker. Question: do I just slap the new paint straight on the wall as-is? Or for the final colour to look 'right' would anyone recommend doing a rough coat of Matt white as a base before hand? Here you can see the test patch of the new paint over the current colour. I'm concerned that the undercoat of teal could give the final colour a slightly different hue. But with the new paint being a lot darker would it be that affected? Thanks!

I don’t know but just bumping to keep near top of questions.

It would make a fabulous flower border, but it depends how much maintenance you are happy to do. If you fill a border completely so no soil shows, this will help keep weeds down. To get rid of the weeds you could dig it over with a garden fork, removing the weeds as you go. A lot of people now use weed flame guns which burn the weeds. Another option is weedkiller but it is horrendous stuff that kills all nature’s mini beasts as well as the weeds so best as a last resort. I’ll be honest you won’t ever kill all the weeds, it’s an ongoing issue. A lot of weeds, like dandelions, air born so they fly in the air and land on soil and then grow. Turf is an option if you don’t mind cutting it each week. Weeds will grow through turf so you still need to remove the weeds before turfing. My last idea is to sow a flower meadow. You can sow seeds or buy meadow turf on a roll and lay that.