On 5 Jun, 17:19, "John" wrote:
I am preparing to Sadolin my window frames - the sills (Cills) on the front
get most of the sun and have some quite bad lengths where the grain has
opened up - beyond the point where I can hope that a thick layer of Sadolin
will fill the cracks. Clearly I need to do something otherwise water will
get in and freeze in the winter and cause further problems. The woodwork is
20 years old - but I hope to get a bit more life out of it.

Can anyone recommend a filler - ideally in a very dark colour - that is
suitable for these quite thin cracks (1mm - 2mm)

Dear John

I know the problem and the solution may not appeal. Once the sill has
degraded to that extent nothing will take to it properly and you will
get failure of paint and filler.
The only sure long-term solution to the problem is to plane off the
ridges or sand them and make the sill that much thinner. If you can
increase the slope on the sill and get rid of any sharp arris to a
radius of say 10 mm, the paint will last longer.

If you have to fill any area then dig out the decayed (usually by UV
light) wood until it is all clean, new wood and I suggest the
following
a) OS borne fungicide brush applied generously on a sunny day with
multiple applications
b) the green Dulux Weather sheild primer to all parts
c) THEN fill with an epoxy resin filler rather than polyester (resins
are normally 50:50 or thereabouts and polyester just has a smidgin of
hardener, like a paste (peroxide?)
I prefer and use a pretty expensive one specially formulated for
wooden windows called "windowcare" - it has a primer resin and two
part filler. It is quite superb and has good planing and other
properties once set
d) once the filler is in those holes that have to be filled sand and
re prime
e) gloss with Saddolins x 2

You will need to regloss every couple of years unlike oil based paint
but no need to strip off

Chris G