How do I prep a painted wall for skimming?

[redhexagonal]

I need to skim this wall after replacing the corner bead. Its already skimmed and painted with matt emulsion which seems sound. I’ve sugar soaped and rinsed the wall. What else should I do before skimming with multifinish? Do I need to key it and PVA or something like that

 

[CBW]

Would be better pva’d. Ratio of 3 to 1, 3 water and 1 pva mix.

 

[lostinthelight]

Bluegrit is what ive been putting on

 

[redhexagonal]

Bluegrit is what ive been putting on

Do you just use that or do you score the wall at all? Is it instead of PVA?

 

[lostinthelight]

If the paint is absolutely solid just blue grit which is pva based.
Some recommend a green grit called Bond-it which they say is easier to put on but ive not tried that.