Gaps between sheets. Best option.

[Restoration man]

Hello.
My old house is sheeted with beaver board. Basically 14mm sheets of wheatabix. It was originally jointed with thick paper tape which could be seen after decoration. I am stripping my hall right back and have removed lose paper tapes to reveal significant gaps of about 25mm between wall and ceiling.

Ive attached a pic looking to the right hand side of the stairwell window where the wall meets the sloped ceiling.

My decorator is going to skim these gaps flush before wallpapering but said obviously I will have to put something in the gap first.

I was thinking a noggin down the back which would be a bit of work but solid. But there is a lot to do.

Any sort of metal mess corner etc I could fix on the face and screw to the posts?

Any other ideas?

Thanks folks

 

[footprints]

Have a Google for plastering beads some batten and some of that should provide a good fixing for plaster.