In message .com, The
Pet Human writes
Can anyone tell me whether I need to sand off all the yellowed stuff?

Doesn't sugar soap shift it?

No, I'm afraid it doesn't.

There _was_ a yellow film on the surface, but I have already washed
that off.

This is the paint itself yellowed.

I'd not worry about it then., just prepare as normal. Don't forget that
white paint yellows a bit anyway with exposure to light.

We had a house that had been owned by a heavy smoker, I don't remember
having any problem with the paintwork on the woodwork..
--
Chris French