Coving

Put it up before, and use ready mixed tile adhesive in a tub, will save you heaps of time and money.

 

As above, cove prior to mist coating the wall. Coving can be a little messy, you’ve got adhesive squishing out from cove edges, (use this to fill any gaps as you clean up), the odd blob dropping onto wall, and sanding down after filling where you’ve got corners and joints along the lengths

All this will make a mess of your mist coat so best to get the messy work out of the way first

Have to disagree with Jord above with using tile adhesive - in my diy experience, tile adhesive on plaster surfaces can affect the paint finish, even with clearing away excess adhesive and wiping down

Powdered Cove adhesive would be my choice, around £12 for 5kg (wickes) goes a long way, easy to work with and clean off excess, can also use to fill gaps / joints / and sand down for a perfect finish

 

Gyproc cove adhesive and a damp sponge to wipe off smudges, small trowel or wallpaper scraper to take away excess at wall and ceiling interfaces, and a1/2" damp brush to wipe the joints to tidy/clean up if need be

 

Spent a lot of time putting up various cove from the 1980s up to circa 2010 ish....then the trend changed and did several jobs that people wanted cove removed....in the back to flat era and preferred rooms with square crisp corners.

Always used Artex to stick the cove up after 5:1 PVA on depth lines to wall and ceilings.

In answer to your question do not mist coat before you put the coving up!

 

When I’ve put coving up I’ve measured depth lines to ceiling and walls and pencil marked them, then scored with cross-cross pattern just where edge of cove will sit on wall/ceiling line

Then, as Astra mentions, 1-5 pva:water mix to seal plaster BUT - work carefully with this as don’t want any pva mix dripping down walls as can cause issues when you come to paint

Work with a small brush and not dripping wet, have wet cloth to hand and thoroughly wipe away any splashes immediately from wall surface. With pva diluted at this rate it has the consistency of water so tricky to accurately work with

The problems caused by pva splashes across walls (say when you have just the ceiling plastered) is a common topic on the forum

 

That's exactly why the PVA is applied to the wall first, it would prevent that from occurring.

Your question was not dumb, it showed awareness so top marks to you.

 

Putting 10mm thick 50mm x 100mm ply blocks nailed to the wall along the depth line about every metre helps support the weight if you are putting the cove up by yourself.

 

Good tip.