Plaster cracks explained: which ones actually matter
Most cracks in plaster are cosmetic and easily made good, but a handful of warning signs mean it is worth getting a crack looked at before you fill it.
Almost every property develops some cracking in its plaster over time, and the vast majority of it is nothing to worry about, caused by ordinary shrinkage, seasonal movement or simple wear rather than anything structural. But because the word “crack” understandably makes people nervous, we get asked to look at a lot of hairline marks that turn out to be completely harmless, alongside the occasional one that genuinely needs proper investigation.
The trick is knowing what to look for. Width, direction, location and whether a crack is actively getting worse tell you far more than how dramatic it looks on the surface. A fine hairline crack across a ceiling is usually nothing, while a stepped crack running diagonally through brickwork and plaster together is worth taking seriously.
This guide walks through the common types of plaster crack we see across Torbay and South Devon properties, what typically causes each, and the specific signs that mean it is time to get a proper assessment rather than just filling and painting over it.
Hairline surface cracks
These are extremely common, particularly on ceilings and in the middle of large wall areas, and are usually caused by the natural shrinkage of plaster as it dries and cures, or by minor thermal movement as a property heats and cools through the seasons. They are typically fine, shallow, and follow no particular structural pattern, often appearing in a random, spidery arrangement.
This type of cracking is cosmetic and can be filled, lightly skimmed or covered with a lining paper without any concern, though it is worth noting that new-build and recently replastered properties are especially prone to this in the first year or two as materials fully dry out and settle.
Cracks around doors and windows
Cracking that radiates diagonally from the corners of door frames and window openings is very common and is usually caused by minor structural movement concentrating around these weak points, where the wall has less material to resist stress. In most cases this is stable, long-standing movement rather than anything actively progressing.
It becomes more of a concern if the crack is wide enough to fit a coin into, if it continues to grow noticeably over a period of weeks or months, or if doors and windows nearby have started sticking or no longer close properly, which together suggest ongoing rather than historic movement.
- Fine, stable cracking from openings is usually cosmetic
- Watch for cracks wider than a few millimetres
- Note whether the crack is growing over weeks or months
- Check if doors or windows nearby have started sticking
Cracks where an extension or new wall meets the original building
It is completely normal to see a crack develop along the junction where a modern extension meets the original structure, because the two sections of building were built at different times, sit on different foundations, and settle at slightly different rates even when constructed correctly. A movement joint should have been built into this junction specifically to accommodate this.
These cracks are generally cosmetic and can be repaired with a flexible filler and joint tape designed for movement, but if the crack keeps reopening repeatedly after being filled, or a visible step forms between the two surfaces, that points to ongoing differential settlement worth having assessed.
Cracks that genuinely need investigating
A handful of specific crack characteristics are worth taking seriously rather than simply filling over. Diagonal, stepped cracking that runs through brick or block joints in a zig-zag pattern, particularly if it is wider than around 5mm or wider at the top than the bottom, can indicate foundation movement or subsidence rather than ordinary settlement.
Cracks that appear suddenly rather than gradually, that run through more than one storey of the building in a continuous line, or that are accompanied by sticking doors, sloping floors or gaps opening up around skirting boards, are all signs that point towards something more significant than cosmetic movement and deserve a proper structural assessment before any decorative repair is carried out.
- Diagonal, stepped cracking through brick or block joints
- Cracks wider than around 5mm, or wider at the top than bottom
- Sudden appearance rather than gradual development
- Sticking doors, sloping floors or skirting gaps alongside a crack
Simple ways to monitor a crack yourself
If you are unsure whether a crack is worth worrying about, a simple monitoring approach is to date and measure it, take a photo with a ruler or coin next to it for scale, and check back every few weeks over a couple of months to see whether it is stable or actively widening. Genuine movement will usually show a measurable change over this period; cosmetic cracking will not.
Crack monitor tape or gauges, sold cheaply at any builders' merchant, give a more precise reading if you want something more reliable than a photo comparison, and are worth using on any crack you are genuinely concerned about before committing to a more invasive investigation.
Getting a crack properly assessed and repaired
For cosmetic cracking, the repair is straightforward: rake out, fill with an appropriate flexible or rigid filler depending on the crack type, and redecorate. For anything that shows signs of ongoing structural movement, the right first step is identifying the cause, whether that is a nearby tree, a drainage issue, or genuine foundation movement, rather than simply repairing the crack and hoping it stays closed.
If you have got a crack anywhere in your home and are not sure which category it falls into, get in touch for a free quote and honest opinion, and we will tell you plainly whether it is a straightforward decorative repair or something that needs a closer look before any plastering goes near it.
Common questions
Should I be worried about a crack across the middle of a ceiling?
In most cases no, this pattern is typically shrinkage cracking, particularly common in older plasterboard or lath and plaster ceilings, and is generally cosmetic. It is only worth investigating further if it is accompanied by sagging, bulging or a crack that continues down into a nearby wall.
Can I fill a crack myself or does it need a plasterer?
Small, stable hairline cracks can often be filled with a flexible decorator's filler and lightly sanded before painting. Larger cracks, or cracks in a ceiling that may indicate a loose plaster key, are better handled by a plasterer who can assess whether the surrounding area is sound before filling.
Does a crack always mean subsidence?
No, subsidence is actually one of the less common causes of cracking, and the vast majority of cracks in domestic properties are down to ordinary shrinkage, thermal movement or settlement at junctions between different building elements, none of which indicate subsidence.
How can I tell if a crack is getting worse?
The most reliable way is to measure its width at a fixed point, photograph it with something for scale next to it, and check again after a few weeks. A genuinely progressing crack will show a measurable change over that period, whereas a stable cosmetic crack will look identical.
Tell us about the job and we’ll come back with a clear next step.
Serving Paignton, Torbay & South Devon. Mon–Fri 08:00–17:00.
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