Fill gap between window and cill - cement or wood?

[StephenStephen]

Hi all,

I've removed the rotten wood below this metal window, and it occurred to me - why don't I fill the gap between the concrete cill and the metal frame (gap height about 45mm high) with concrete rather than wood? - any thoughts or comments greatly appreciated, thank you.

 

[KenGMac]

StephenStephen, good evening [again]

My preference is to replace with timber, if you opt for cement, there is a very high probability of the cement cracking over time and allowing water to enter.

Suggest you have a look at something like

https://www.ebay.co.uk/itm/Hardwood...Timber-Sills-Threshold-FREE-P-P-/113232691320

Ken