Not all cracks are serious: some are purely cosmetic while others reveal a structural problem. This guide helps you identify the type of crack and assess its severity.
The Different Types of Wall Cracks
Micro-Cracks (< 0.2 mm)
Appearance: Very fine, hair-like lines Causes: Natural shrinkage of plaster, humidity variations Severity: Very low - cosmetic issue only
Fine Cracks (0.2 to 2 mm)
Causes: Minor building movement, thermal expansion and contraction Severity: Low to moderate - requires monitoring
Significant Cracks (> 2 mm)
Causes: Foundation settlement, structural problem Severity: High - expert assessment is mandatory
Major Cracks (> 5 mm)
Causes: Serious structural problem, subsidence Severity: Very high - potential danger, urgent expert assessment required
Diagnosis Chart
| Type | Width | Severity | Action |
|---|---|---|---|
| Micro-crack | < 0.2 mm | Low | Simple filling |
| Fine crack | 0.2-2 mm | Moderate | Monitor + repair |
| Significant crack | 2-5 mm | High | Assessment + treatment |
| Major crack | > 5 mm | Very high | Urgent expert assessment |
Warning Signs Requiring Expert Assessment
- A crack that is growing wider over months
- A crack that goes all the way through the wall (visible on both sides)
- Width > 2 mm on a load-bearing wall
- Doors or windows that no longer close properly
- Staircase-pattern cracks running over several metres
Solutions and Costs
Micro-Cracks and Cosmetic Cracks
- Filler compound: €10-30 (DIY)
- Tradesperson intervention: €100-200
Stabilised Structural Cracks
- With reinforcement mesh: €30-50 per linear metre
- Professional total: €150-400
Active Structural Cracks
Foundation underpinning:
- Mini-piles: €3,000-8,000 per pile
- Resin injection: €2,000-5,000
Crack stitching: €800-2,000
How to Monitor a Crack: The Tell-Tale Method
- Apply a strip of plaster across the crack
- Mark the date on it
- Monitor over 3-6 months
- If the plaster strip cracks: expert assessment is necessary
Cost of a Structural Expert Assessment
- Basic assessment: €300-600
- In-depth assessment: €800-1,500
- Contradictory assessment (both parties): €1,500-3,000
Find a Mason on tack.lu
More than 100 professional masons are listed on tack.lu in Luxembourg.
FAQ
Are all cracks serious?
No. Micro-cracks (< 0.2 mm) are generally superficial and not dangerous. They result from the natural movement of building materials.
Can a crack repair itself?
No. A crack never closes by itself. It may stabilise, but it will always require repair.
How long should I monitor a crack?
A minimum of 3-6 months using a plaster tell-tale, ideally over a full seasonal cycle to capture thermal expansion and contraction.
