I'm about to paint a toilet room, it has cold water to hand basin (so there's been no steam in the room) with semi-gloss.
The walls are cement rendered, and were painted in semi-gloss about 10 yrs ago.
The existing paint is in good condition.

What prep work needs to be done?
Would a wash with sugar soap do, or do I need to lightly sand, or both?

Thanks....
(I hate painting)