When cracks and damp appear together, it’s a red flag that something more serious than a simple cosmetic issue is happening. Damp and cracks are often connected, and treating one without addressing the other will lead to problems. This guide explains what’s happening and what needs to be done.
How Damp and Cracks Are Connected
Damp and cracks have a two-way relationship.
Cracks allow damp in: When water finds a crack in your wall, it penetrates through to the materials behind. Over time, this moisture can spread, causing deterioration and damage to the structure itself. A crack that starts as a minor cosmetic issue becomes a path for water infiltration.
Damp creates cracks: Moisture damages materials, causing them to deteriorate, weaken, and crack. Salt deposits left behind as water evaporates also damage mortar and plaster. The material becomes friable (crumbly) and fails, creating visible cracks.
This means that simply filling a crack when damp is present doesn’t solve the problem. You’re sealing in the moisture and preventing it from drying out, which can make the problem significantly worse.
Types of Damp That Cause Cracks
Different types of damp have different causes and require different solutions.
Rising Damp
What it is: Water seeps up from the ground into your walls, like a sponge absorbing water from a wet surface.
Why it happens:
- Ground moisture is drawn up through the porous materials in your walls
- Often indicates a failed or missing damp-proof course (DPC), which is a barrier designed to prevent this
- More common in older properties that lack proper DPC
- Can occur in properties with defective DPC systems
Visual signs:
- Damp patches that are concentrated near the base of walls
- Usually extends up to 1-1.5 metres from ground level
- Pattern is often a distinct tide line of discolouration
- Smell of mustiness at ground level
- Peeling wallpaper or paint near the base
- Crumbling plaster, particularly at the base
How it causes cracks: Rising damp damages the mortar and plaster it affects, causing them to weaken and crack. The cracks are usually horizontal or close to ground level. The affected areas become soft and friable.
Severity: Medium to high. Rising damp requires investigation and proper remedial treatment.
Penetrating Damp
What it is: Water enters from outside, penetrating through the external walls or roof. It’s driven in by wind and rain rather than rising from below.
Why it happens:
- Defective external materials (cracked render, damaged brickwork, failed mortar joints)
- Missing or damaged roof tiles
- Blocked gutters and downpipes
- Inadequate external drainage
- Cracks that allow water entry
- Missing or damaged weatherproofing
Visual signs:
- Damp patches on external walls, particularly above ground level
- Often worse on the side of the building facing prevailing winds
- May appear during or after heavy rain
- Discolouration on external and internal wall surfaces
- Peeling paint or wallpaper in concentrated areas
- Possible signs of water running down internally after rain
How it causes cracks: Water penetrating through external materials deteriorates brickwork and mortar. Freeze-thaw cycles (water freezing and expanding in winter) accelerate damage. The damaged material becomes weak and cracks. Cracks are often found where water is entering, particularly around windows and doors.
Severity: Low to high, depending on the cause. A leaking gutter is easy to fix. Structural damage to brickwork requires more work.
Condensation
What it is: Water vapour in the air condenses on cold surfaces, creating moisture on walls, windows, and other surfaces.
Why it happens:
- High humidity in the home (from cooking, washing, showering, drying clothes)
- Poor ventilation trapping humid air
- Cold surface temperatures (poor insulation)
- Temperature differences between inside and outside
Visual signs:
- Moisture on windows and cold surfaces
- Occasional damp patches (particularly in bathrooms and kitchens)
- Possible mould growth on cold spots
- Pattern often follows where cold bridges exist (corners, around windows)
- Smell of mustiness in affected areas
How it causes cracks: Condensation alone doesn’t usually cause structural cracks directly. However, repeated condensation can damage plaster and paint, and combined with poor ventilation and cold walls, can create conditions where mould and material deterioration occurs. This may contribute to surface cracking over time.
Severity: Low to medium. Usually manageable with ventilation improvements and avoiding excessive moisture generation.
Identifying Which Type You Have
| Type | Location | Pattern | Timeline | Associated Issues |
|---|---|---|---|---|
| Rising damp | Ground level, extends upward | Tide line pattern | Gradual onset, worsens in winter | Musty smell, crumbling plaster near base |
| Penetrating damp | Usually above ground level | Irregular patches | Often worse during or after rain | Following rain patterns, near openings |
| Condensation | Particularly corners, windows | On cold surfaces | Daily/seasonal pattern | Associated with humid activities |
How Damp Damages Materials and Causes Cracking
Understanding the mechanism helps explain why damp is serious.
Damage to Mortar
Mortar joints between bricks are porous and vulnerable to damp. When water penetrates:
- Salts in the water are deposited as water evaporates
- These salt crystals expand and contract with moisture changes
- This process (called salt crystallisation) causes mortar to crumble
- Weakened mortar fails, creating gaps and causing cracks to spread
- Brickwork loses structural support where mortar has failed
Damage to Plaster
Wet plaster deteriorates through:
- Softening and weakening as it absorbs moisture
- Loss of adhesion to underlying surfaces
- Mould growth within the material
- Salt deposits damaging the plaster structure
- Freeze-thaw cycles in winter (in unheated spaces)
Freeze-Thaw Damage
In cold weather, water in materials freezes:
- Ice expands, creating internal pressure
- This breaks down the material structure
- When it thaws, tiny cracks and damage remain
- Repeated cycles cause significant deterioration
- This is particularly damaging to brickwork and mortar
What You Might Notice
If you have damp-related cracks, you’ll likely observe:
Visual signs:
- Cracks appearing alongside damp patches
- Discolouration around or near the cracks
- Plaster appearing soft, spongy, or crumbly around the crack
- Mould or algae growth near the crack area
- Paint bubbling or peeling around the crack
Smell:
- Musty or earthy odour
- Mould smell if fungal growth is present
Feel:
- Affected wall feels cold or damp to touch
- Plaster feels soft rather than hard
- Area might feel colder than surrounding walls
Pattern:
- Cracks following specific lines (like horizontal tide marks for rising damp)
- Multiple cracks concentrated in one area rather than scattered
- Cracks that worsen seasonally (worse in winter)
Why Simply Filling the Crack Won’t Work
This is crucial to understand: if you fill a damp-related crack without addressing the damp, you’re likely making things worse.
What happens:
- You fill the crack with filler
- Moisture continues to penetrate the wall behind the filler
- The filler seals the surface, trapping moisture inside
- Moisture accumulates and spreads
- Material behind the filler deteriorates
- The crack reopens, or new cracks appear
- Mould and dampness problems worsen
The result:
You’ve wasted money on a failed repair and potentially worsened the underlying problem. You now have trapped moisture and accelerated deterioration.
The Correct Approach: Diagnosis First
If you have damp-related cracks, the proper sequence is:
Step 1: Identify the damp type
Is it rising damp, penetrating damp, or condensation? The location, pattern, and timing give clues.
Step 2: Find the cause
- Rising damp: Is there a missing or failed DPC?
- Penetrating damp: Are there cracks in render? Damaged brickwork? Faulty gutters? Failed mortar joints?
- Condensation: Is there poor ventilation? Excessive moisture generation?
Step 3: Get professional assessment
For anything beyond condensation, professional diagnosis is important. Get:
- A damp survey from a qualified damp specialist
- Identification of the cause
- Recommendations for remedial work
- Advice on insurance implications (if relevant)
Step 4: Address the cause
This is the crucial step. Fix what’s causing the damp:
- Rising damp: Install or repair the DPC
- Penetrating damp: Repair external damage, fix gutters, repoint mortar, etc.
- Condensation: Improve ventilation, reduce moisture sources
Step 5: Allow the wall to dry
Once the cause is addressed, the wall needs time to dry out. This can take weeks to months depending on severity.
Step 6: Repair any damage
Only once the wall is dry should you:
- Remove damaged plaster
- Repair or repoint mortar if needed
- Apply new plaster or finish
- Fill and repair cracks
Treatment Options for Different Damp Types
| Damp Type | Primary Treatment | Timeline | Cost Indication |
|---|---|---|---|
| Rising damp | DPC injection or new DPC installation | 1-2 weeks treatment, weeks to dry | £1000-3000 |
| Penetrating damp (gutter issue) | Repair/replace gutters and downpipes | Days to weeks | £300-1500 |
| Penetrating damp (render/brickwork) | Repoint mortar, repair/replace render | Weeks | £500-2000 |
| Penetrating damp (around openings) | Repair or replace windows/doors, reseal | Weeks | £500-3000 |
| Condensation | Improve ventilation, extract fans | Immediate | £100-500 |
Red Flags That Need Professional Help
Contact a damp specialist or surveyor if:
- You see rising damp (tide line of damp at ground level)
- Damp is widespread or increasing
- You see crumbling mortar or brickwork
- Damp persists despite ventilation improvements
- You’re seeing mould growth
- The crack pattern suggests penetrating damp
- You’re unsure about the cause
- Damp has persisted for months despite weather improvements
- You’re concerned about structural integrity
Preventing Damp-Related Cracks
Prevention is better than cure.
Exterior maintenance:
- Keep gutters and downpipes clear
- Ensure proper external drainage
- Maintain render and pointing
- Address any cracks in brickwork or external materials promptly
- Trim back trees that create damp conditions
- Ensure windows and doors are properly sealed
Interior management:
- Ventilate kitchens and bathrooms well
- Avoid drying clothes indoors excessively
- Run extractor fans during and after cooking/showering
- Maintain reasonable indoor humidity (30-50%)
- Heat rooms adequately in winter
Regular inspection:
- Check for new damp patches regularly
- Address small problems before they become large
- Monitor cracks to catch deterioration early
- Keep gutters and drainage clear
Insurance Considerations
Important points about damp and insurance:
- Most home insurance does not cover damp damage
- Damp is often considered a maintenance issue rather than a covered peril
- Subsidence causing damp might be covered under subsidence policies
- You may need specialist damp insurance (ask your insurer)
- Damage from a specific event (burst pipe, extreme weather) might be covered
- Pre-existing damp is typically not covered
Always inform your insurer about damp issues, but don’t expect coverage unless it’s from a specific insured event.