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Most cracks we are called to are cosmetic. A small number are not, and the difference is usually readable without any equipment.
Written by a civil engineer with thirty years of looking at buildings, on the principle that you should be able to triage your own wall before paying anyone.
Start with width
Use a coin as a gauge — everyone has one, and it is more reliable than a guess.
Hairline, barely catches a fingernail → almost always shrinkage or thermal movement in the plaster or render. Cosmetic. Extremely common in this climate.
Visible but you cannot insert a coin edge → usually still cosmetic, worth monitoring.
A coin edge fits → worth proper attention.
Wider than a coin edge, or you can see through it → stop. Do not fill it, do not paint it. Get it assessed.
Then direction and path
Fine random cracking, map-like, over an area → shrinkage in the finish coat. Cosmetic.
A straight line following a junction between materials — where blockwork meets concrete, or around a column or beam. Two materials moving at different rates. This needs treating as a movement joint, not filled solid, or it simply reopens.
Diagonal from the corner of a door or window → often thermal, sometimes not. Openings concentrate stress. Monitor it.
Stepped, following the mortar joints in blockwork → take seriously. Get advice.
Passing straight through blocks rather than around them → take seriously. It takes more force to split a block than to open a joint.
Horizontal, part-way up a wall → uncommon and worth advice.
Then behaviour — the test that actually settles it
Width and direction give you a likelihood. Movement gives you an answer.
Mark and date it. Pencil a short line across the crack at its widest point and write the date beside it. Photograph it with a coin for scale. Repeat in three months, and again after a season change.
Not moving → whatever caused it has stopped. Cosmetic repair is appropriate.
Widening → something is still happening. Get advice before any repair.
This costs nothing and it is more informative than any opinion offered on a single visit, including ours.
Signs that change the picture
A crack matters more if it comes with any of these:
- Doors or windows that have started sticking or no longer latch
- Floors that feel less level than they did
- The same crack appearing on both faces of a wall
- Several cracks appearing at once, across different rooms
- Any crack that has reopened after being properly repaired
Any of those together with a crack of real width is the point at which a structural engineer's assessment is the right spend, not a decorator.
Why this climate produces so many harmless cracks
Al Ain has intense sun for most of the year and a wide daily temperature swing — a fifteen degree drop between afternoon and night is routine in summer, with inland highs reaching 38 to 44°C against 35 to 41°C on the coast. Every material on the building expands and contracts through that cycle, every single day.
Finishes are thinner and less flexible than what they are applied to, so they crack first. That is why fine cracking in plaster and render is normal here in a way it is not in a temperate climate, and why most of what alarms people is genuinely nothing.
It is also why external repairs need fillers with the right flexibility. A filler harder than the surface around it simply cracks around its own edges — the repair fails at its perimeter and people conclude the crack "came back".
Repairing a cosmetic crack so it stays repaired
- Cut it out. Open the crack to a V so the filler has something to hold. Filling a hairline on the surface fails
- Clean it. Dust is the commonest reason a repair lets go
- Use the right material for the substrate and exposure — flexible where there is movement
- Reinforce where the crack follows a junction — tape or mesh, or form a movement joint
- Prime, then paint across the full wall, not the patch
Skipping step 1 is why most DIY crack repairs reappear within a year.
Where we stop
If we think a crack may be structural, we say so and recommend a structural engineer's assessment rather than repairing it and hoping. Filling a structural crack hides the evidence and makes the eventual diagnosis harder and more expensive.
For repairs: civil maintenance and painting and wall repair.
Related: what your ceiling stain is telling you · villa maintenance checklist