Wood filler vs Silicon

[NatB]

Hi,
I've finished stripping down and repairing my wooden sash windows and would like to get them at least undercoated to get them through the winter.

The window frames have some substantial gaps in places through a century of movement and would like to fill or seal these.

Is an exterior grade filler or caulk/silicon preffered for this type of thing and should I fill, rub down then undercoat or undercoat then fill?

 

[big-all]

do NOT use silicone it wont take paint
best to use a hard filler so you can rub it down
if its a large area you need to cut out and splice in or at minimum if its decay get rid off all soft wood you can use stabilising/hardner solution specificly for wood repair then specific exteriour filler

 

[gorgeousgordy]

Are the gaps between the box frame and the exerior wall or actually in the box grame?

 

[foxhole]

Flexible car body filler tends to be cheaper and stronger than a lot of purpose made timber fillers.