Replacing rotten window sill

I spoke to window fitter. He said take off a bit so you can wedge it underneath then use expanding foam to keep it in place
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When I’m busy with stuff like this, I clearance drill and deep countersink the add on piece, flood the joining area with exterior adhesive, offer up and use two long screws. When all’s cured I fill the countersink with car body filler, apply brown silicone where appropriate and then paint and more paint.
John :)
the correct way to do cill mitres is to plane then sand a radius on the top edge and the front.

then coat the cill ends fully with your sadolin,

then when dry, fit cill and then put a bit of brown sealant in the V groove you formed by the sanded radius

face fix from outside and cover with wooden plugs
Ok so put sticks like **** on it and expanding foam underneath. What a mess! Should have cover everything with masking tape before doing it. Is it a case of just sanding this mess out?

On a positive note. It doesn't seem to want to move


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As good as new
Just gotta put sealant in


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