A good reply from the'Omnipole Man', Though I would slightly qualify the fact that you can do a top job on windows with oxidized, powdery frames.
Once they have started to oxidize the flaming things don't stop
It's the one area where you will do a better job with trad methods. You can do a fair job with WFP, but until the windows are re-painted it won't be perfect.
I either turn down work of this nature, or demonstrate to the potential customer with a moistened finger what the problem is, they either accept that I will not be able to do a perfect job, or, with a resigned shrug I'll try and pass the work along to a trad cleaner, cos I'm not interested in doing domestic work the trad way.....Actuall, having said that, I do have one account where I do a mixture of WFP and trad because of some windows that are starting to oxidize
They have to accept it with the upstairs (they have a mixture of UPVC and Wooden) but on affected downstairs windows I do clean them the 'old' way.
But I do accept that Glyn has way more experience than me!!
On most windows, at least for myself, I spend a lot of time on the top edges of each pane of glass, er, timewise that is kinda relative of course!
On a first time clean my method is the same as the one Glyn described.
Most of the time I would expect to do a job that was top notch, even on a first time clean.
Not every window will sheet, it is the ideal for sure if it does, but some will bead up instead, not a lot you can do about that, but you should still do a top job, you might have to use more water though to ensure there is nothing trapped in the water beads that will cause the windows to spot when it dries out.
Regards,
Ian