Plasterboard On A Ceiling

[Johnny7seven]

Just moved in. The garage ceiling is plasterboarded only it's started coming down along the edges and bowing in the middle a bit. Obviously a DIY job. It's fixed along the beams rather than across them. So I'm going to have to refix it. But on my own. It's going to be a sod of a job so I'm using two Acrow props, 50mm screws, 2x2 batten where needed on 12mm boards.
That sound about right?

[The Builder]

Before you even start Johnny. If you mean ordinary gypsum plasterboard, then I'm afraid that's really not ideal in a garage.

It'll keep on bowing forever, no matter how you fix it. Gypsum is "hygroscopic" meaning it readily soaks up water. It'll keep taking water vapour out of the atmosphere until it may even, eventually, turn to mush.

Unless....... you might get away with water-resistant plasterboard (used in showers.)
Better still but more expensive would be something like "Masterboard" or "Supalux". They are a sort of replacement for the old asbestos boards.
Local builders' merchants will have them or something similar.

[Johnny7seven]

Thanks Mr The Builder. It's not bowing that badly yet so I'll try to head it off by shoring it up, maybe putting ply on it to protect it then replace the lot at a later date.
Does the A row method sound doable?

[The Builder]

Johnny. I guess when you mention Acrows, you mean to hold a board up in place while you fix it?

It'll work, but Acrows are pretty heavy to handle, and a bit "overkill."
What I always use are things we call "trees."
A length of 2x1 batten just a bit longer than the height of the ceiling. (A bit of trial & error here.)
Fix a 2' length of 2x1 right at the top at right-angles. (Making a T-shape.)
Nail on a short (1') piece of 2x1 as a diagonal brace to stop the crosspiece from going out of whack.
Sounds complicated, but should take only a couple of minutes to make.

Jam the tree under a bulgy bit and screw the board into place.
It's how I hold up a whole 8x4 sheet of plasterboard and fix it on my own.
Hope I've understood you right.