www.ultimatehandyman.co.uk

Sorry for the poor photo but you get the idea.

In the window frame shown there's a gap right at the end where light is coming through. The gap is 2mm wide, 60mm deep and 1220mm from top to bottom.

I did Google but ended up getting confused. Don't want to use acoustic caulk if I should be using expanding foam or whatever. Thanks.

ttt

i cant see a gap anywhere ???

Thanks, mate. I've drawn an arrow where the gap is.

If the gap is only 2mm them go the mastic route. Frame sealant of whatever colour suits for the outside and a run of decorators caulke on the inside should you need to touch up paintwork. It'll take you longer to go and get the mastic than it will to actually apply it. An alternative may be to fit a timber quadrant or bead on the inside but frankly a bead down just one side would look odd and for cosmetics you'd need to go around the whole window. Stich with mastic.

Thanks, pal, very helpful.