dried out white marks on walls

[slayer]

Hi Guys

Got some plastering done in my house and there are white marks like dust on it.

we had cavities cleared as a lot of crap in them and the guys put the browning on and then skimmed over it with board finish.

on the line where the browning met the normal plaster there is a white dust appeared is this normal? it did take a little while to dry out but it is all dry now.

any info appreciated.

Slayer

[welsh brickie]

White powdery stuff is effloresance its salt content in the material.just brush it off.