What is causing this?

[markus250]

Hi all,
We've recently discovered a section of paint on the wall in our back room is turning powdery and coming off the wall if touched. A good few years ago the room had a fresh skim of plaster to smooth the walls. Plaster sealer was used then the room was painted. Paint used at that time was Crown matt emulsion. A few years later we repainted the room in Dulux Light and Space paint. All was ok but we're now seeing this area going dusty.
Its not an external wall as the wall is connected to next door. Room is well ventilated, area of paint going dusty seems dry to the touch. Until recently we had no carpet and the floor was taken up to fit some plug sockets. Nothing damp or anything that would cause any leaks under the floor (we had noticed the dusty paint before carpet was fitted). I sanded the dusty paint off the wall and used a Zinser product (i forget the name now) which was specifically for problem areas. I then repainted the wall and its now going dusty again.

Any ideas? I do know next door has their oven on the other side of the wall and their kitchen etc but this has always been the case and never had any problems before.

Picture below:

 

[DiyNutJob]

Maybe be heat from next door is coming through. Have a feel with the hand at times when they are most likely to be cooking. If there was moisture, it would have killed your skirting board. If the problem is caused by biology, you can kill whatever is there with bleach. Many products including some paint contain food for mini-life.