One of the most important things to understand about wall cracks is the difference between a structural crack and a superficial one. This single distinction can mean the difference between a simple cosmetic fix and a serious building problem. Let’s break it down in plain language.
What’s the Difference?
Superficial cracks affect only the outer layer of your walls. They’re surface-level damage that doesn’t compromise the structural integrity of your building. Think of them like a scratch on your car’s paint job. It looks bad and you might want to fix it, but the car is still safe to drive.
Structural cracks go deeper. They indicate that the actual building structure is moving or under stress. They affect the materials that hold your house up and could suggest serious underlying issues. These are the equivalent of a crack in your car’s frame rather than its paint.
The tricky part? It’s not always obvious which type you’re dealing with.
Quick Comparison Chart
| Factor | Superficial Crack | Structural Crack |
|---|---|---|
| Location | Only in plaster or render | Affects brickwork, concrete, or timber |
| Pattern | Random, single, or scattered | Horizontal, diagonal, or stair-step pattern |
| Width | Usually under 3mm | Often 5mm or wider |
| Direction | Often vertical or random | Often horizontal or diagonal |
| Growth | Stable over time | Growing or changing |
| Associated damage | None nearby | Sticking doors/windows, other cracks |
| Cause | Drying, settling, weathering | Building movement, subsidence, structural stress |
| Fix required | Filler and redecoration | Professional repair, possible investigation |
How to Tell the Difference
Check What Layer It’s In
The most reliable way to identify a structural crack is to work out which layer of your building it’s affecting.
Superficial cracks stay in the plaster or render (the smooth outer coating). If you can see the crack is only in this outer layer, and the brickwork or underlying material looks fine, it’s superficial.
Structural cracks go through the plaster and into the material beneath. If you can see cracks in the actual brickwork, concrete, or mortar joints (rather than just the plaster), that’s a structural issue.
Look at the Pattern
Different crack patterns tell different stories.
Likely superficial:
- Random, scattered fine cracks
- Single vertical cracks
- Cracks confined to one small area
- Cracks around fresh paintwork or new plaster
Likely structural:
- Horizontal cracks (especially full-width across a wall)
- Diagonal cracks running at a 45-degree angle
- Stair-step cracks that follow brick joints
- Multiple cracks forming a pattern
- Cracks appearing in several rooms or on multiple walls
Consider What Comes With It
Structural cracks rarely appear alone. They’re usually accompanied by other signs of building movement.
Superficial cracks might have:
- Peeling paint or damp plaster nearby (but no deeper damage)
- Perhaps some discolouration from weathering
Structural cracks often come with:
- Doors or windows that stick or won’t close properly
- Other cracks appearing elsewhere in the property
- Visible displacement (one side of the crack is higher than the other)
- Damp patches or moisture problems
- Crumbling mortar in brickwork
- Bulging or bowed walls nearby
Test the Depth
Here’s a practical test you can do yourself:
- Run your fingernail along the crack. Does it catch on anything, or does it slide smoothly?
- Tap the wall on either side of the crack with your knuckles. Does it sound solid, or hollow?
- Look at it from an angle with strong light. Can you see the crack continuing into the deeper material, or does it stay on the surface?
If the crack is shallow and only affects the plaster, it’s likely superficial. If it appears to go deep into the wall, it needs professional assessment.
Check the Edges
Look carefully at the edges of the crack.
Superficial cracks usually have clean edges. The plaster on either side of the crack is in similar condition.
Structural cracks often have rougher or more damaged edges. The plaster around the crack might be crumbling or deteriorating. You might see dust or debris in the crack itself.
Common Causes
Understanding what caused the crack can also help you identify its type.
| Cause | Type | Explanation |
|---|---|---|
| Plaster drying out | Superficial | Normal process as new plaster cures |
| Normal house settling | Superficial or Structural | Minor settling = superficial; major settling = structural |
| Temperature changes | Superficial | Plaster expands/contracts with heat and cold |
| Poor workmanship | Superficial | Incorrect plaster application or preparation |
| Subsidence | Structural | Ground beneath home is moving or sinking |
| Foundation issues | Structural | Problems with how the building sits on the ground |
| Structural movement | Structural | Walls shifting due to age, stress, or damage |
| Moisture and damp | Can be both | Causes deterioration; structural if affects masonry |
| Vibration (nearby traffic) | Superficial or Structural | Depends on severity and building condition |
The Age of Your Property Matters
New Build Properties (Less Than 5 Years Old)
New builds commonly develop superficial cracks as the materials settle and dry out. Hairline cracks in plaster are very normal. However, multiple wider cracks or cracks in structural materials should still be investigated, as they might indicate construction defects.
Older Properties (10+ Years Old)
Older homes may have some structural cracks as part of normal aging. However, if cracks appear suddenly or grow noticeably, it warrants investigation. Age itself doesn’t mean cracks aren’t important.
Victorian and Georgian Properties
These older buildings often have cracks and are usually more forgiving about movement. However, newly appearing cracks should still be assessed, as they might indicate issues that need addressing to preserve the building.
When Superficial Becomes a Problem
Even though superficial cracks are less serious structurally, they can become problematic if:
- Moisture gets into them and causes damp problems
- They’re so numerous that large areas of plaster are affected
- They keep reappearing after being filled
- They’re affecting other materials like render or brickwork underneath
What to Do Next
If you think it’s superficial:
- Monitor it over the next few months to make sure it’s not growing
- Once you’re confident it’s stable, you can arrange for it to be filled and decorated
- This is a straightforward job that most plasterers or decorators can handle
If you think it’s structural:
- Don’t assume the worst, but do get professional advice
- Contact a surveyor or structural engineer for a proper assessment
- They’ll identify the cause and recommend appropriate fixes
- Early action often prevents bigger problems developing
If you’re genuinely unsure:
- Take photos and measurements
- Document any other signs like sticking doors or other cracks
- Contact a professional for peace of mind