Gap between wooden window frame and stone cill. Very damp. Bad weather. How to fill and resolve!

13 Nov 2020
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United Kingdom
I’m not expert at DIY but I am practical and willing to learn.
I have a window at about 15ft from ground which I have discovered has a large 1inch gap between bottom of wooden window frame and what looks like stone window ledge.
Window has been neglected (have two small kids and as younger one now 18 months at trying to get to grips with more things!)
Obvious damp below window inside and in top of room below where on occasion of rain coming from certain direction water literally pours down the wall.
Have now painted window as best I can and removed the inch of failed sealant from gap. The gap looks cavernous. Window ledge which is about 6ft long, is divided into three blocks. I’ve removed flaky masonry paint and The end block is very damp and sandy. It’s a 1960s rebuilt house with very solid render over what I presume is brick.
1) I have tried to get tradesmen interested abs failed
2) need to make this gap waterproof ASAP
3) in Scotland. Weather generally wet and windy. Exposed location. Plastic cover blows away. It is not going to fully dry out before I repair
3) can reach cill at chest height but not am not confident with heights (terrified) and nervous of for example injecting expanding foam because if I get it wrong I’m not confident I’ll have the purchase to remedy it. (Sawing could be difficult etc)
4) there is a piece of torn black plastic kind of folded in the gap. Is this a rudimentary damp course??? Do I need to replace with similar?
5) is some kid of mortar my best option? Which I extend over sash window cill? Would I then put bead of sealant / silicone between mortar and wood?
In average get max one hour slots to attack the job!
In preference would like a thorough long lasting solution.
All advice grateful received. Thank you
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28 Jul 2015
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United Kingdom
Don't suppose you could post a pic?

Perhaps expanding foam may be better then cut flush once dried, you can render if needed, with or without some kind of mesh.

Folk will give better opinions, if they can see the issue.

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