IMHO, the main problem is the wood that's used these days - unless you pay a fortune.
After altering my kitchen I fitted a new wood Magnet window - just a plain large window with one opening casement. And despite it being made of pressure treated timber and me keeping it painted, both the sill and the top part were rotten within about 15 years. All my sash windows are original Victorian - although some may have had repairs.
I used to use white wood-primer, leaving it for the client to paint. But they'd often use all sorts of cheapo paint and even just gloss straight on to the primer - so windows start rotting 5/10 years on. I got around this by using grey aluminium yacht primer - it's so dark that you need 2 or 3 undercoats to cover it - result: good paint cover. Pity they can't make wood primer in black with purple spots. I also tell them to clean often - with a chamois leather and just clean water, and to look out for defects in paintwork during the first few years and to remedy them immediately - there's bound to be a knot lifting or paint not sticking on a greasy bit. The point is to blame them in advance for anything going wrong!
cheers
Jacob
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