Additional skim causing blistering paint??

[YouTarzanMeJane]

I am in the process of moving the sink in my bathroom and on removing the tiled splashback found that the previous tiles had been laid before a previous plaster skim. We had had problems with the wall paint blistering which we had assumed was maybe because there was too much vinyl-y paint stopping the walls from breathing properly, but now are wondering whether the additional skim may be the issue? If so what is the solution? Obviously there is no skim in this area (it is now back to the original wall - the tile marks you can see are presumably the original tiles not the ones we just removed) but there still is across the rest of the room and we recently had the chimney that passes through the room removed so that has been plastered and some has obviously been smoothed over onto the original wall meaning that transition now has 2 layers of extra skim. Is this likely to be the problem with the blistering paint? What can I do now to avoid it again in future?

And following on from this, how to I fill the thickness to level off the wall? Most of it won’t have the new splashback on it so ideally I want to back to a nice smooth wall. Is there anything I can do myself or do I need to get it properly plastered?

The red circled area on the photos is the bare brick, with the original plaster on top, then above it, circled in green, is the additional skim and the blue shows the recent transition overlap where the old chimney was removed.

Thanks

 

[dontbelieveawordofit]

skim wont cause blistering paint. poor preperation causes blistering paint.
i’d remove the sink and scrape all loose material off.
then prepare the whole wall and skim it all to one level.