Wrong time of year I know, but I want to do this as soon as it starts to
warm up so best to be prepared.

The back of our 3 storey house faces south so, even in these less than
tropical climes, it gets a lot of sun and (sometimes) heat. We have an
array of sash windows, each with a stone cill on the outside. Much of
the paintwork on the timber is holding up for the moment (with a few
exceptions) but the cills are in a bad way, with curls of paint
(multiple layers) flaking off. The cills at the front are nowhere near
as bad. I presume the problem started with poor surface preparation on
the first coat and/or there has been some incompatibility with
subsequent layers.

Whatever the issue, I'll have to scrape the cills back to bare stone and
start again. On the basis that the bare stuff being exposed to the
elements for a bit shouldn't be a problem, I'll go through them in turn,
then paint the lot in (hopefully) one go, ideally in the spring without
the full force of the sun on the job as I'm painting.

So - what's the paint to use in this circumstance? I don't really want
to spend a load of time on this only for it all to peel off again and I
don't mind spending a bit to ensure the job's a good 'un in the long
term. Although it's not such an pressing problem, any experience with
painting wood in this position would be appreciated too as there are a
few places that could use a lick.

Cheer chaps.