TL;DR
Cracked walls and ceilings are common in Melbourne homes, and most of the time they’re caused by house settling, seasonal ground movement, or ageing plaster rather than anything serious. The trick is knowing which cracks are cosmetic and which ones are warning signs. This guide walks through the usual causes, how to tell a harmless hairline crack from a structural one, what a proper plaster repair involves, and why the DIY filler-and-forget approach almost always fails within a year. If you’re seeing new or widening cracks in your home, our team offers a free plastering assessment and quote to get to the bottom of it.
Cracked Walls or Ceilings?
Common Causes of Cracked Plaster
Cracks don’t appear for no reason — plaster is a rigid material sitting on top of a house that’s constantly shifting, however slightly. Here are the usual culprits we see across Frankston, Mornington, Narre Warren, and the rest of Melbourne’s south-east.
House settling. Every home settles after construction as the frame, foundation, and soil beneath it adjust to the load. This is normal and usually produces small, stable hairline cracks in the first few years of a build.
Seasonal ground movement. Melbourne sits on a lot of reactive clay soil, particularly in the south-east suburbs. Clay expands when it absorbs moisture over winter and contracts as it dries out in summer. That constant swelling and shrinking moves the footings slightly, and the plaster above transmits that movement as cracking — often around door frames, window corners, and cornices.
Moisture issues. Leaking roofs, poor drainage, plumbing leaks behind walls, or rising damp all weaken plaster and cause it to crack, bubble, or crumble. Moisture-related cracking is usually accompanied by staining, a musty smell, or soft, spongy patches.
Age of the property. Older homes often have plaster that’s simply reached the end of its serviceable life. Decades of minor movement, temperature changes, and previous patch-up jobs add up, and the plaster becomes brittle and prone to cracking.
Structural movement. Less common, but more serious. Cracks caused by footing failure, tree root interference, or genuine structural shifting tend to be wider, run diagonally, and keep growing over time.
Minor Hairline Cracks vs Serious Structural Cracks
Not every crack needs an engineer — but every crack deserves a proper look. Here’s how to tell the difference.
Width. Hairline cracks are generally under 1–2mm wide — about the thickness of a coin or thinner. Anything wider than 5mm, or a crack you can fit a fingernail into, warrants closer inspection.
Pattern. Fine, web-like cracks or straight vertical lines along a cornice or plaster joint are typically cosmetic. Diagonal cracks (especially those running at 45 degrees from a window or door corner), stair-step cracks in brickwork, or cracks that appear on both sides of a wall in the same spot are more concerning.
Whether they’re growing. This is the most reliable indicator. A crack that’s stayed the same size for years is almost certainly stable. A crack that’s visibly widened, lengthened, or reappeared shortly after being filled is telling you something is still moving. Doors or windows that have started sticking around the same time are another red flag worth noting.
If your cracks are narrow, stable, and not paired with sticking doors or sloping floors, they’re very likely cosmetic and straightforward to repair.
The Plaster Repair Process
A proper repair isn’t just running some filler along the crack and calling it done — that’s exactly the shortcut that leads to cracks coming back (more on that below). Here’s what a correctly executed plaster repair looks like:
- Cleaning out the crack. Loose, crumbling, or flaking plaster is raked out and the crack is widened slightly so the new filler has something solid to key into. Dust and debris are cleared so the compound bonds properly.
- Filling and setting. A suitable jointing or setting compound is applied in thin layers, often with a paper or fibreglass tape embedded across the crack for reinforcement — particularly important on cornices and joints where movement is likely to recur.
- Sanding. Once cured, the area is sanded back flush with the surrounding surface, so there’s no visible ridge, lip, or texture difference once painted.
- Priming for paint. A sealer or primer is applied over the repair before painting. This stops the patched area from flashing (showing through as a different sheen or colour) once topcoats go on.
Done properly, this process leaves a repair that’s genuinely invisible and durable — not just hidden until the next change of season.
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When Cracking Might Indicate a Bigger Structural Issue
Most cracks we’re called out for are entirely manageable with standard plaster repairs. But a small number point to something underneath that needs addressing first. Get an engineer’s opinion before any cosmetic repair if you notice:
- Cracks wider than 5mm, or ones that have grown noticeably over a few months
- Diagonal cracking radiating from door and window corners
- Cracks that line up on both the inside and outside walls in the same location
- Doors or windows that have started jamming or no longer close flush
- Visible gaps opening up between walls and ceilings, or walls and floors
- Sloping or uneven floors developing alongside the cracking
If any of these apply, it’s worth getting a structural engineer to assess the footings and frame before spending money on plastering — otherwise you’re just papering over a problem that will resurface. Once the underlying cause is addressed, our team can carry out the plaster repair with confidence it will hold.
Why DIY Crack Filling Often Fails
It’s tempting to grab a tube of filler from the hardware store on a Saturday afternoon, and for a genuinely tiny hairline crack, that might hold for a while. But for most cracks, DIY filling fails within months, and here’s why:
- Wrong product for the job. Many off-the-shelf fillers are rigid once cured and have no flexibility, so when the house moves again (which it will, especially with Melbourne’s clay soils), the crack simply reopens along the same line.
- No reinforcement. Without embedded tape across joints and cornices, a filled crack has nothing holding the two sides together — it’s cosmetic, not structural.
- Skipped prep. Filling straight over loose or crumbling plaster without cleaning it out first means the repair has nothing solid to bond to.
- Uneven finish. Under-sanded or poorly blended patches often show up as a different texture or sheen once painted, especially in raking light.
The result is a repair that looks fine for a few weeks, then reopens or becomes visible again — meaning the job gets done twice. A professional repair, using the right compound, reinforcement, and finishing process, is built to actually last.
FAQ
How much does plaster crack repair cost in Melbourne?
It depends on the number, size, and cause of the cracks, as well as whether ceiling or wall areas are involved. Small hairline repairs are relatively inexpensive, while larger or recurring cracks may need a more involved fix. We provide a clear, itemised quote after assessing the property.
Can cracked plaster be a sign of a bigger problem with my house?
Sometimes, yes. Most cracks are cosmetic and caused by normal settling or seasonal ground movement, but wider or widening cracks — particularly diagonal ones near windows and doors — can indicate structural movement and should be checked before repair.
How long does a plaster repair take?
Small hairline crack repairs can often be completed in a day, including drying time between coats. Larger repairs, or those involving multiple rooms or ceiling areas, may take a few days to allow proper curing before painting.
Will the crack come back after repair?
Not if it’s repaired correctly with proper cleaning, reinforcement, and setting compound suited to the movement involved. This is the main difference between a lasting professional repair and a quick DIY fix that reopens within months.
Get a Free Plastering Assessment
If you’re noticing cracks in your walls or ceilings, don’t guess whether they’re harmless or something more. Our team provides honest, experienced plastering assessments across Frankston, Hastings, Karingal, Keysborough, Langwarrin, Mornington, Mount Martha, Narre Warren, Patterson Lakes, Pearcedale, Seaford, Skye, and the surrounding Melbourne south-east suburbs. Learn more about our team, browse our completed work in the gallery, or get in touch today for a free assessment and quote.
