How to fix ceiling cracks?

[nugley]

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.

[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.