Preparing external paintwork

[hemelhandyman]

I've been asked to repaint all external wooden windows and french doors; problem is, existing putty is stable (ie not loose) but has hairline cracks every 25mm or so along its length.
I think that cracks are too shallow to apply filler but also too wide for coats of undercoat and gloss to fill
Does anyone have any suggestions as to how to prep?
All responses gratefully received!

 

[benno5]

if the putty is rock hard mate and not loose ,give it a good rub down and rub some more putty into the cracks ,once its had a couple of coats of undercoat and a coat of gloss it should be fine