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How to fix ceiling cracks?

As shown in the image, I have 3 ceiling cracks. These cracks run in between ceiling joists that are spaced 600mm. There is a noggin behind the middle crack which the plasterboard is attached to. My current thoughts is that the middle crack needs a PVC expansion joint, but I'm not sure about how to solve the outer 2 cracks. I'm reaching out to the community in the hope of understanding what is the best and longest-lasting way to fix these cracks based on other people's experiences.

Note: I've recently started to glue and screw any loose parts of the ceiling to the joists. I believe this may help to minimise re-cracking in future.

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JacobZ

Hi @nugley,

Ceiling plasterboard often cracks at corners and direction changes because these areas carry the most stress as the building moves with temperature, humidity and settlement. Any small movement in the framing transfers force to the plasterboard, and joints at corners are the weakest points, which makes them a likely point for cracking.

For this reason, installing a Plaster Expansion Joint across that middle crack is certainly going to be worthwhile and will have the most effect in minimising future cracking. It will allow the plasterboard at the corner to flex with the different movements of the framing.

The top and bottom cracks can be managed by v-grooving them with a utility knife to open them slightly, ensuring you wear gloves while doing so, then applying mesh tape over the groove and coating with Multi-Purpose Joint Compound before sanding and painting. These cracks are less likely to recur with the installation of the expansion joint, and the mesh tape will help to strengthen them to prevent further cracking.

Alongside the expansion joint and crack repairs, your efforts in screwing and gluing the plasterboard back to the joists will also help to reduce unexpected movement, which is a cause of cracking. This, combined with the expansion joint and mesh tape repair, is about the best you can do in this situation.

Let me know what you think and if you have any further questions, please let me know.

Jacob

nugley

Thank you for the detailed response @JacobZ. Really appreciate it. Yea, I'm just looking for what's the best I can do in this situation. Just trying to minimise future cracking that's all.

I do have a couple of questions if that's ok.

Currently, behind the middle crack there exists a 90 x 35mm timber piece that is screwed into the joists and the plaster is glued and screwed into this timber piece (red outline in the image below). The cracks have formed in between the two joists. Would it be best to unscrew the plaster from this timber piece or possibly detach the plaster from the timber piece before installing the expansion joint?

I'm thinking this timber piece is what may have caused the two outer cracks.

For the 2 outer cracks, would there be any value of adding any backing (plaster or timber) behind them (green outlines in the image below) before v-grooving them and then applying mesh tape and joint compound?

Hopefully I'm not over-engineering this one lol.

JacobZ

Hi @nugley,

For your expansion joint to work effectively, the plasterboard needs to overhang its fixing points slightly. This would more or less mean that there is a timber framing piece in the location of the two green rectangles, and the expansion joint sits between them, where the red rectangle is. The plasterboard would be fixed to the framing at the location of the green rectangles using glue and screws.

Do you have any photos of the framing that sits above this? It is hard to picture where things run, so a visual would certainly help.

Also, seeing the back side of the plasterboard would help, as I think some of the issue is down to where the plasterboard was joined. I think some of the cracking might be superficial and runs through the plaster compound rather than the board, so assessing the location of the actual join in the plasterboard would help.

Let me know what you think.

Jacob

nugley

Hi @JacobZ.

Thank you for the reply. I appreciate all your help.

I've managed to get a photo of the framing sitting above it and placed it side-by-side to the photo from ground level. I've also included a photo showing roughly where the cracks run in relation to the framing.

The ceiling plasterboards have been screwed into 2 timber noggins that run perpendicular to the joists, and directly above or nearby the 3 cracks. The actual sheet join can be seen to the right of the timber noggins. Hopefully this gives you a better picture of what's happening up top.

The 2 timber noggins and screwing of the ceiling into the noggins was done about 10 years ago. Personally, I'm thinking that the screws into the timber noggins have contributed to the forming of the 2 outer cracks as the sheets have slightly moved and slightly sagged over time. By unscrewing the ceiling from the 2 timber noggins and by using an expansion joint in the middle crack, I'm thinking this will help minimise the 2 outer cracks from re-cracking in future after they've been repaired.

But, I would be interested in hearing your thoughts.

EricL

Hello @nugley

Thank you for sharing that extra picture of your ceiling. It is definitely a possibility that the extra timber frame could be the cause of the plasterboard cracks. I propose installing an expansion joint right over the red square in your description. This will accommodate the movement from both sides which are the green rectangles. I don't recommend fixing these sections in place as the majority of movement is occurring in this spot. It's highly likely because of the walls nearby as they expand and contract with the change of temperature, they affect the roofing frame as well.

If you need further assistance, please let us know.

Eric

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