How to fill gap below window sill?

[gtman600]

Hi I currently want to fill the bottom of a gap below a window that is about 90mm following the installation of new windows in a double brick house.

I am planning to install a 40mm thick wood window sil and so there will be a gap of 50mm and I was wondering what materials could I use to pack and support the window sil that also could be plastered to finish the wall below the window.

[JacobZ · Accepted solution]

Hi @gtman600,

Welcome to the Bunnings Workshop community, it is fantastic to have you with us.

I'd suggest installing either a piece of 70 x 45mm H2 Framing or 90 x 45mm H2 Framing, whichever fits the depth of the brick better.

You should use plascourse on its underside so that it is not in direct contact with the brick as moisture can transfer from the brick to the timber if unprotected.

You can use Green Wall Plugs with 75mm timber screws to fix it in place.

You wouldn't get a great result plastering directly over this timber, so you should set it back from the edge of the brick by 10mm, so you can install a strip of 10mm plasterboard over the timber, which can then be set and finished the same as the brick.

Let me know what you think and if you have further questions, please don't hesitate to ask.

Jacob