Help with chalky residue on walls? (pics)

[dotexe]

Hi all hope somebody can help me here. Long story short we recently had a disaster where a grinder had been used inside our house and coated everything in cement dust. I have cleaned the house top to bottom. Including hoovering and wiping down the walls. When I run my fingers along the ceiling or walls they are chalky and I'm not sure if this is dust or simply the paint coming away? I know the coloured paint used on the walls is Dulux Matt Emulsion from B&Q.

Any help or advice much appreciated.

 

[sparkwright]

I have Dulux matt emulsion (from 2001) and that leaves a chalky dust when you touch it.

 

[dotexe]

Thanks for your response. I am beginning to think it is the paint. These walls have been painted 2 years but there is a similar thing happening with our newly painted walls but to a lesser degree (same paint).