Filling under window board (with pics)

Hi all,

Found when I took the plaster off the walls (1930's semi) that the top course of bricks (internal leaf) under my windows was just sat there with no mortar, plastered over with the gap between bricks and window boards "filled" with plaster. I've mortared the bricks in:



(don't laugh too much, my first go at bricklaying )

The original window boards are still there (pink color in the picture), with a UPVC cover. They are supported by a few pieces of timber set into the mortar between the bricks.

Question is, what should I do with the the (1cm or so) gap between the window board and brick? Do I need to put some wedges, expanding foam, ...?

Expanding foam but not to much you could just lift the window board.

http://www.screwfix.com/prods/43569...g-Foams/No-Nonsense-Expanding-Foam-Hand-750ml

Thanks, will go slow - been told before it's scary stuff