"Barrier" paint?

[Rooster]

3 hours ago, Viking said:

Thanks for the information.

So this has to be done even if these walls were built 20 years ago?

I looked at the picture again and it appears isolated to that area. This is just a guess. Is it possible that you or a laborer can enter above the ceiling and examine the top of the hollow blocks above where the paint is separating from the concrete? It's possible that a roof leak dripped on the top of the hollow blocks, seeped down to that area and caused that to happen.  Look to see if there is no dust compared to other areas and look for a possible leak roof that may be "contributing" to that.

Edited February 21 by Rooster

[Viking]

13 hours ago, Rooster said:

I looked at the picture again and it appears isolated to that area. This is just a guess. Is it possible that you or a laborer can enter above the ceiling and examine the top of the hollow blocks above where the paint is separating from the concrete? It's possible that a roof leak dripped on the top of the hollow blocks, seeped down to that area and caused that to happen.  Look to see if there is no dust compared to other areas and look for a possible leak roof that may be "contributing" to that.

Thanks for trying to help me finding the reason for the problem.

In fact, this exist in a few other places as well, but much smaller, no bigger than the size of a hand.

I will get up on the  ceiling and see what it looks like from there 👍

The paint is actually not separating from the concrete, it's just a discoloration. All of them appear in chest/belly hight.

[hk blues]

17 hours ago, Viking said:

That's actually not a bad idea, hahaha.

I will cover the problem with a book shelf in the yellow room, but if possible without going through to much hassle, I want to avoid it happening again in the rooms I am about to repaint.

You said earlier that you have had different results with different brands of paint, which paint did you feel were better?

I tend to use Boyson but Davies is equally good in my opinion.  Island paint is also OK but from my experience it tends to discolour in the can/tin more than the other two although it does cover better. I'm also a fan of Titan but it's limited in availability. 

Do NOT buy Rain and Shine (not to be confused with Davies Sun and Rain) - it requires way more coats than the others.