How to fill gaps behind architrave?

[VNylen]

Hi, I've been having an office built out the back and it's ready to have the archs and skirts installed.  My plan was to learn how to do this myself and I've done a lot of googling and watching the diy vids.  My problem is that there is a huge gap from the frame of the window to the plaster.  I thought the plasterer was going to pack it so that the plaster came flush with the frames, but I must have misunderstood him.  My problem is now I'm not sure how to resolve the gap that will be behind the archs if I install them as it is.  I'm a bit stumped and in need of some help please and thankyou

         

[JacobZ]

Hi @VNylen,

Thank you for your question and welcome to the Bunnings Workshop community, it is great to have you with us.

Can you advise how far past the plasterboard the window casing protrudes? 

Depending on how far the casing protrudes, you could install a secondary piece of timber such as a 42 x 18mm 5.4m Moulding White Pine FJ Primed DAR on the face of the plasterboard to create a flush surface to attach the architrave to both the casing and the timber mounted on the plasterboard. You would then simply need to caulk around the edges with Selleys No More Gaps.

Let me know if you require further explanation, or if this doesn't work for you, there may be other options I can provide.

Jacob

[VNylen]

It's about 10mm past the plasterboard

[JacobZ]

Hi @VNylen,

Something like this 42 x 11mm 5.4m Moulding White Pine FJ Primed DAR might be more suitable then. Once gap filler is added around the shadow lines, a 1mm variation will be imperceptible.

You would just need to ensure that any brad nails used are long enough to go through your chosen architrave, the 42x11mmm timber, 10-13mm of plasterboard and still give good embedment into the framing timber behind. Something around 45mm should suffice.

Let me know if you require further assistance or clarification.

Jacob