30mm gap between plasterboard and ceiling - board up or fill?

[Deluks]

Is your existing board skimmed and painted, or painted direct to the board? A plasterer may be able to recommend a primer to improve adhesion. Or you may be able to scuff up an existing skim coat to do the same.
It sounds like these questions would be better off in the plastering forum.

 

[RookieTony]

Thanks @Deluks! I will make sure to stick to plastering forums in future. But I think I am nearly done with prep for this project - gauging how well the specific AC50 acoustic sealant will stick to the existing wall is the last item I would love to check with experts on these forums!

Here is the existing wall with skirtboard removed:

To my layman's eye it looks like either light skimmed or painted directly - I can't tell!

 

[RookieTony]

View attachment 294324

What application pattern do they mean? Where would the bead start and what are the centers the manual is referring to?

Is it basically this?

 

[If in doubt...]

That is brilliant, thank you @If in doubt...

I don't suppose you could help me figure out the following bit from the AC50 manual:
View attachment 294324

What application pattern do they mean? Where would the bead start and what are the centers the manual is referring to? I've googled it and couldn't find any drawings.

The manual goes on to say that "Highly porous substrates such as new plaster should first be primed with Everbuild PVA bond diluted 1:4 with wa-
ter."
But this woulnd't apply to an existing painted plasterboard, would it?

You don't need to be too precise with the application, basically I would run a bead all around the perimeter, say an inch or so in from the edge and then run some vertical full length lines within that perimeter bead - approx 250 mm apart. Whether it is fresh new plasterboard or old plaster you can never go wrong with applying a watered down PVA solution beforehand.

 

[RookieTony]

Big thanks to everyone for contributing! The PVA mix is drying on the wall overnight, and tomorrow the plasterboard will go up

 

[RookieTony]

Thanks to everyone for contributing! Here are the results:

And with plastering done by a local professional: