Filling Gap under Window

[Spinny]

How do people suggest I fill the gap under my floor level window as shown in the photo ? (Around 16mm)

As you can see the Window was installed onto plastic spacers before being screwed in, so I need to fill between and around the spacers. A porcelain patio is planned to be laid up to the window frame, or possibly with a strip of gravel soakaway at the bottom of the window.

 

I am thinking ideally an element of insulation might be good at the back of the gap to limit thermal bridging at the frame ?

And perhaps mortar mix, or concrete mix, or Toupret exterior rock solid repair filler in the front half of the gap ?

[Andeh]

I wanted expanding foam, but builder insisted on packing it tight with mortar to ensure the packers and window stayed secure. Looking back, I'm pleased I let him. I used expanding foam at the top and sides though. With the movement of the door, if it nudges those packers out post patio install ya'll in for a world of trouble. 

 

 

Edited 4 hours ago by Andeh

[Russell griffiths]

 

pump 3 tubes of this under it, stop 20 mm from the packers and let it dry for 48 hrs

then chop the packers off flush with a sharp chisel, then fill the remaining gap and wipe over the ends of the packers. 
will dry more solid than mortar, won’t crack and fall out.