We do refurbs in London ,I generally scud coat, scratch next day,I always rule it to see what the wall is like firstly,fill in any hollows if need be, leave it beaded and set for a week then second it,I just like it nice and flat and level as possible, I have seen many new jobs, OCR,mono etc destroyed by it not been ruled flat, the sun grasses the spreads up, some massive developments around London destroyed by amateurs, not saying you of course ,probably cheap as chips two week coursers.i am new to the game since 1987 used to do 250k of work a year since the late nineties but only a quarter of that now. I tried to get into property but the recession put me back on the trowel. Lots of spreads rule the first coat .