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Hi,
We have a water-soaked insulation batt that caused the center of the ceiling plasterboard to sag.
We've already stopped the leak before the water managed to get through the batt and damage the ceiling board itself.
Since the sag is in the center of the plasterboard, and we're just rookies, we did some research.
It seems the first step is to use a plasterboard lifter (or T-brace) to push the board back into a flat position ?
 
After that, we should use Zenith 8G x 50mm Gold Passivated Bugle Head Plasterboard Screws to secure the board back into the timber joists—does that sound right?
But what if there are already screws in the joist? Should we use a scraper to remove the surface layer to find and remove the old screws? ðŸ«
Then we’ll use self-adhesive reinforcement tape to cover the crack.
Is there a very strong tape you'd recommend for this?
Hi @ivanptr,
It looks like the water has gotten into the ceiling board and weakened it. If it were just the insulation holding moisture, you likely wouldn’t see such noticeable sagging and cracking. In this case, the best approach would be to cut out the damaged section and replace it with a new plasterboard panel. A plasterer could likely take care of it in a few hours.
You could try pushing the board back into place and adding more fixings, but there’s a good chance the panel will still be compromised. Even with reinforcement tape and filler, the amount of patching needed could remain quite visible, and the board may not sit completely flat against the ceiling. If you do decide to attempt the repair, make sure to check for existing screws and remove them before adding new ones, as they could stop the sheet sitting flush against the ceiling joists.
Plaster repair tape is used for fixing cracks, but it's not designed to hold a sheet together; that's a structural issue that requires replacement of the sheet.
Please let me know if you have any questions.
Mitchell
Today we got a headache when the tradies gave us a quote of $960. ðŸ«
So now, we're planning to fix it ourselves.
The plasterer said there’s no need to remove the cornice, and that got us thinking — why not? It seems like the joist is above the cornice.
 
Do you think we can replace the plasterboard without removing the entire sheet — just by leaving the old board near the cornice?
Anyway, tomorrow I’ll start by removing the old board and let you have a look.
I hope we can resolve this step by step..🤕
 
Hello @ivanptr
Before you take the ceiling apart, I need to ask you how old is your house? Was it built between 1970 and 1980s? If it was, I suggest having your ceiling tested for asbestos first before you take it apart. If the test is positive, you'll need an asbestos removal specialist to remove the asbestos. If the test is negative, you can proceed with the removal of the ceiling board. It might be possible to remove only the damaged section and patch the ceiling.
Eric
Our brain trust @EricL @MitchellMc
 
The house was built in 2000. I tried cutting out some of the sagged section, but the area near the cornice (marked by the blue arrow) is still sagging. I also tried pushing that section up to the joist (yellow point) to see how it would look with a new screw, but it still continued to sag.
Our question is: can we just cut along the red line and install a new board, leaving the cornice intact? It seems more straightforward and time-saving 😂ðŸ«
Hello @ivanptr
I recommend stopping for a moment and consider removing the cornice in order to remove the entire sheet. The type of repair you are doing now is taking a lot of time with trial and error. Plus, you will not get a proper flat finish. By installing a new panel, you can be sure that the ceiling will be flat, and you will not have to do a lot of plastering. I suggest using a multi tool to remove and cut the cornice.
If you need further assistance, please let us know.
Eric
Hi @EricL
If we use a multitool to remove the cornice, is it likely that we’ll damage it and need to buy a new one?
What do you think about adding a timber batten instead? Which type of timber batten can we purchase from bunnings ?
We used Photoshop to visualize our idea :
Hi @ivanptr,
You should cut back to the middle of the surrounding timbers and screw them off to the timbers every 15cm around the opening. You can then cut your replacement section of plaster to match the whole size. You then be able to install it with Stud Adhesive and screw it off to the exposed sections of timber around the perimeter.
By cutting back the current plaster halfway through the timbers, you'll be able to attach both the old and new plasterboard to the timber as per my rendering below.
Mitchell
 
@MitchellMc Good morning
Thank you for the tip — we'll try this technique on the right side!
Apologies, our computer-generated image is not accurate enough
The joist on the left side is above the cornice, and we’re now struggling with whether to cut the cornice—risking damage and the challenge of finding a replacement—or to add a timber batten instead
Any advice on this ? ðŸ«
I'd add a timber batten instead @ivanptr. Is that joist proud of the cornice at all? Could you cut the plaster back right up to the edge of the cornice to expose the joist and fix the edge of the new plaster?
Mitchell
