sugar soap 
noun [mass noun] British
An alkaline preparation containing washing soda and soap, used for cleaning surfaces or removing paint.If you are papering over paint, first clean the walls with sugar soap to make sure the paper sticks....
- With two helpers - one to guard the anchorage and ropes and another to man a boat in the river below - they began their first task, to take off all the old paint with sugar soap and a wire brush.
- Now I'm going to wash it down with sugar soap, allow it to dry over lunch and then paint the walls and ceiling this afternoon.