how to get smooth finish on a wall with old paint patches

[MrDodgy]

Hi fellas,

I'm trying to paint a wall that's prone to condensation and mould.
I've scrapped away the patches of old paint that were flaky and
I'm left with what you can see in the picture, with part of the surface covered with old paint, and part stripped down to the plaster.

I plan to paint with Zinsser BIN on the areas with bare plaster, and
then with one or two coats of Zinsser Permawhite to make a mould
resistant finish.

The problem is that I think the edge of the patch of old paint will still be visible when I've finished. I've tried sanding the ridge as much as I can with coarse, and then medium sandpaper, but I can still
feel it with my finger tips.

What are my options for dealing with this?
I don't want to line with paper due to the condensation problems. I have wondered about using Polycell basecoat to even things up a bit, but have read about it making damp problems worse. Any ideas?

thanks in advance. View media item 82099 View media item 82099

 

[Bosswhite]

sand down the edges and then fill with fine surface filler and "feather off"

 

[WabbitPoo]

Have you attacked the cause of the condensation and mould? That'd be high on my agenda first.

 

[MrDodgy]

thanks for the replies.

@Bosswhite: does "feather off" mean sanding with fine paper?
After posting yesterday I found that putting Polyfilla on the edge of the old paint patch, and then smoothing off with a wet scraper seemed to produce a reasonable result.

@WabbitPoo: the condensation is there because the wall gets very cold in winter. Its a solid wall in a ground floor conversion flat. I do what I can to reduce the amount of water that gets into the air, but ultimately the real solution would be to fit proper wall insulation. Unfortunately that would involve my landlord opening his wallet, which isn't going to happen.

 

[Bosswhite]

You could try a coat of Coovar Anticondensation paint, then a couple of coats of Diamond Matt Emulsion or Eggshell,
Dont forget to wash down walls with antifungicidal solution first
Materials are expensive but should last.