How to fix a sagging ceiling?

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 ?

file_00000000ff8051f69cb835f5c009a89a_conversation_id=67ec90da-bdf8-8009-8951-a4c056983fc5&message_id=0594ddbe-ee6b-4830-95e4-537b3d016231.jpg

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? 🫠

Then we’ll use self-adhesive reinforcement tape to cover the crack.

Is there a very strong tape you'd recommend for this?

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Comments

MitchellMc

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

ivanptr

https://www.workshop.bunnings.com.au/discussion/comment/50677#Comment_50677

Today we got a headache when the tradies gave us a quote of $960. 🫠

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..🤕

EricL

https://www.workshop.bunnings.com.au/discussion/comment/87450#Comment_87450

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

ivanptr

https://www.workshop.bunnings.com.au/discussion/comment/109260#Comment_109260

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 😂🫠

EricL

https://www.workshop.bunnings.com.au/discussion/comment/121971#Comment_121971

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

ivanptr

https://www.workshop.bunnings.com.au/discussion/comment/130034#Comment_130034

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 :

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/135091#Comment_135091

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

ivanptr

https://www.workshop.bunnings.com.au/discussion/comment/138440#Comment_138440

@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 ? 🫠

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/140672#Comment_140672

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

ivanptr

https://www.workshop.bunnings.com.au/discussion/comment/142306#Comment_142306

@MitchellMc @EricL

No, the joist is completely behind the cornice — it doesn’t extend beyond it at all. Today, we used a multitool to cut along the cornice joint without removing the cornice .

Feeling excited — making small progress today ! All the sagging sections have finally been removed. 🫠 heaps of thanks for guiding us

The blue line joist is fully occupied by the adjacent existing ceiling board, and the yellow lines are available for the new board.

1. What are the best locations to install the timber battens?

2. Which screws should we use? The joist thickness is about 3.4 cm. How many screws do we need on each side of the batten?

3. For the timber from Bunnings — what size and type should we get ?

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/143474#Comment_143474

Hi @ivanptr,

As mentioned previously, the first step is to cut the opening back to halfway across the thickness of the roof joists. If that can't be done in some places, you would need to install batons in those areas. Currently, you have numerous edges that are not cut back to the nearest joist. Perhaps your blue line above is, but all other sides are not and are unsupported. Every edge and join needs to be supported behind with timber.

100mm long screws would be suitable, and I'd use 70 x 35mm Pine for shorter batons and any longer lengths 90 x 45mm.

I've marked in red below where you'll need batons to be placed.

Mitchell

ivanptr

https://www.workshop.bunnings.com.au/discussion/comment/144356#Comment_144356

Hi @MitchellMc ,

Could you please reupload the picture that shows where to place the battens? It looks like the image didn’t attach above.

Thank you so much.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/145001#Comment_145001

So sorry @ivanptr. The battens need to be placed all around the perimeter of the cutout section.

Mitchell

ivanptr

https://www.workshop.bunnings.com.au/discussion/comment/145509#Comment_145509

@MitchellMc

The red line marks a joist that’s located behind the cornice, so it's not accessible to support the new plasterboard.

The yellow lines indicate the exposed joists we can use, and the white lines represent the timber battens we’re planning to install.

Does the new plasterboard need to be supported on all four edges by either a joist or a timber batten? We’re unsure how to support the bottom edge, as installing a batten there would require it to be quite long and difficult to secure.

Or if possible , could you mark where you think the timber battens should be installed?

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/145898#Comment_145898

Hi @ivanptr,

If you take a look at the image below, you'll see how every edge of the repair sheet needs to be positioned over a joist. If you can not cut the boards back so the repair sheet is over a joist, you need to install new timbers in those positions.

You've seem to have noted in white most of the required location, though there are still unsupported areas, as pointed out by the arrows below.

Mitchell

ivanptr

https://www.workshop.bunnings.com.au/discussion/comment/146207#Comment_146207

Hi @MitchellMc , today we managed to solve an issue. We used a multitool to remove the cornice on one side. The cornice remained intact, so there's probably no need to replace it

This means that side of the new plasterboard can now be secured directly to the joist without needing a timber batten — saves us some elbow grease 🫠

However when we inspected the other side with cornice , we noticed that the original plasterboard wasn’t secured to any joist at all.

1. So we still need to install a timber batten. But there's a metal plate blocking the area, making it difficult to screw the batten in. What should we do?

2. If on one side the joist is too close to the brick wall, and there isn’t enough space to use a screwdriver to fix the timber batten. Is there another way? Can we use some L-shaped metal brackets?

JacobZ

https://www.workshop.bunnings.com.au/discussion/comment/146466#Comment_146466

Hi @ivanptr,

Anywhere that you can't get in behind the truss to screw back into your timber, you can use either Dunnings 60 x 60 x 70mm M10 Galvanised Angle Brackets or Pryda Joist Hangers - To Suit 45 x 90mm to attach your timbers.

To deal with the nail plate on the truss, you can attach a piece of timber to the side of the truss that is long enough so that you can screw it into the timber on either side of the truss. You can then attach your batten as if the nail plate weren't there.

Let me know what you think and if you have further questions, please don't hesitate to ask.

Jacob

ivanptr

https://www.workshop.bunnings.com.au/discussion/comment/146677#Comment_146677

Hi @JacobZ @MitchellMc ,

We found that the holes on the angle bracket are too big for our screws

(Zenith 10-8 x 100mm Galvanised Countersunk Rib Head Timber Screws - 50 Pack).

What do you think about using a different-sized bracket

A medium-sized one?

Or a smaller one?

We are using 70 x 35 mm timber (Framing MGP10 H2 Blue Pine), and each batten is less than 100 cm in length.

JacobZ

https://www.workshop.bunnings.com.au/discussion/comment/146848#Comment_146848

Hi @ivanptr,

Some smaller brackets would be fine as long as they have at least two screw holes on each arm of the bracket.

A pack of these Carinya 40 x 40 x 40 x 2mm Galvanised Reinforcing Angle Brackets would work well at a relatively low cost.

Just make sure you use at least 2 of the screw holes on each side of the bracket.

Let me know if you have any further questions.

Jacob

ivanptr

https://www.workshop.bunnings.com.au/discussion/comment/146991#Comment_146991

@JacobZ @MitchellMc @EricL

Making slow progress—hope that's alright 🫠

JacobZ

https://www.workshop.bunnings.com.au/discussion/comment/147101#Comment_147101

It's coming along nicely @ivanptr.

I'm excited to see it when you are done.

Jacob

ivanptr

https://www.workshop.bunnings.com.au/discussion/comment/147207#Comment_147207

Good morning @JacobZ @MitchellMc @EricL

We’ve attached all the battens on the four edges.

The opening size is 177cm x 120.5cm.

Right now, we have one plasterboard panel:
Gyprock 1200 x 900 x 10mm Repair Panel

How should we arrange this?
Do we need to buy two more sheets?
And how much would we need to cut off?

How much space we need to reserve between two sheets ?

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/147299#Comment_147299

Hi @ivanptr,

It would be better to use one 2400 x 1200mm sheet and cut it down to the exact size of the hole. That would minimise the number of joints. Though I understand that it will make installation more difficult. If you are to use multiple smaller sheets, you'll need to ensure, once again, that all their edges are supported by timbers behind them.

For positioning, the 1200mm length matches your 1205mm opening, which would be the logical way to position it. You'll then need a second sheet cut down to 870 x 1200mm to fill the rest of the gap.

Mitchell

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