Rising damp and penetrating moisture can destroy your home’s interior walls, creating unsightly stains, peeling paint, and health-threatening mould. Internal damp proofing offers an effective solution when external work isn’t possible or practical.
This guide shows you exactly how to damp proof walls from the inside, covering everything from identifying damp problems to choosing the right treatment method for your specific situation.
What Is Internal Damp Proofing?
Internal damp proofing creates a moisture barrier on the inside surface of your walls. Unlike external treatments that stop water at the source, internal systems manage moisture that’s already penetrated your walls.
You’ll typically choose internal damp proofing when:
- External walls are inaccessible
- Listed building restrictions prevent external work
- Cost constraints limit your options
- You need a quick temporary solution
The method works by installing a physical barrier between the damp wall and your internal decorations. This stops moisture from reaching your plaster, paint, and furnishings.
Types of Damp That Affect Internal Walls
Rising Damp
Water travels up through your walls from the ground via capillary action. This happens when your damp proof course (DPC) fails or doesn’t exist.
Signs include:
- Tide marks up to 1.5 metres high
- Salt deposits on walls
- Musty odours
- Peeling wallpaper at skirting level
Penetrating Damp
Water enters through external wall defects like cracked mortar, damaged pointing, or faulty guttering.
Signs include:
- Damp patches that worsen in wet weather
- Staining that appears after heavy rain
- Cold spots on internal walls
- Mould growth in specific areas
Condensation
Warm, moist air meets cold surfaces and creates water droplets. This isn’t technically damp proofing territory, but often gets confused with other damp problems.
Signs include:
- Water droplets on windows and walls
- Mould in corners and behind furniture
- Problems worse in winter
- Issues mainly in bathrooms and kitchens
How to Identify Your Damp Problem
Before starting any internal damp proofing work, you must identify the exact cause. Getting this wrong wastes money and fails to solve your problem.
Visual Inspection Method
Step 1: Check the pattern of damp
- Rising damp creates horizontal lines
- Penetrating damp follows water entry points
- Condensation appears randomly across surfaces
Step 2: Test during different weather
- Monitor damp patches during dry and wet periods
- Penetrating damp worsens with rain
- Rising damp remains fairly constant
Step 3: Use a moisture meter Electronic moisture meters (available from £15-50) give accurate readings. Take measurements at different heights and compare with dry areas.
Professional Survey Options
For complex cases, consider hiring a damp surveyor. The Property Care Association maintains a directory of qualified specialists.
Expect to pay £300-600 for a comprehensive survey, but this investment prevents costly mistakes.
Internal Damp Proofing Methods Explained
1. Tanking Systems
Tanking creates a waterproof barrier across the entire internal wall surface.
Best for: Severe rising damp, below-ground rooms, persistent moisture problems
Materials needed:
- Waterproof render or membrane
- Mesh reinforcement
- Specialised primer
- Finishing plaster
Advantages:
- Completely waterproof barrier
- Works on severely damaged walls
- Long-lasting solution
Disadvantages:
- Expensive (£40-80 per square metre)
- Reduces room size
- Professional installation recommended
2. Damp Proof Membrane (DPM)
Plastic or bituminous sheets fixed to walls before replastering.
Best for: Moderate damp, DIY projects, cost-effective solutions
Materials needed:
- Polythene or specialist membrane sheets
- Mechanical fixings
- Battens for air gap
- Standard plasterboard
Advantages:
- Relatively inexpensive (£15-25 per square metre)
- DIY-friendly
- Quick installation
Disadvantages:
- Reduces room dimensions
- Risk of condensation behind membrane
- Limited effectiveness against severe damp
3. Damp Proof Paint and Sealers
Specialised coatings that penetrate wall surfaces to create moisture barriers.
Best for: Minor damp, temporary solutions, maintenance work
Materials needed:
- Damp proof paint or sealer
- Wire brush for preparation
- Primer (if required)
- Standard decorating tools
Advantages:
- Minimal room reduction
- Easy application
- Cost-effective (£8-15 per square metre)
Disadvantages:
- Limited effectiveness
- Requires regular reapplication
- Won’t solve severe damp problems
4. Electro-Osmotic Systems
Electronic devices that reverse the electrical charge causing rising damp.
Best for: Rising damp in solid walls, heritage buildings, minimal disruption solutions
How it works: Electronic units create an electrical field that pushes moisture back down into the ground.
Advantages:
- No structural changes required
- Suitable for listed buildings
- Long-term solution
Disadvantages:
- High initial cost (£1,500-3,000)
- Controversial effectiveness
- Requires electrical installation
Step-by-Step Internal Damp Proofing Process
Phase 1: Preparation and Assessment
Step 1: Safety first
- Turn off electricity to affected areas
- Wear protective equipment (gloves, mask, goggles)
- Ensure adequate ventilation
Step 2: Remove existing finishes Strip wallpaper, paint, and plaster up to 300mm above visible damp damage. Damp often extends higher than visible signs suggest.
Step 3: Clean the wall surface
- Wire brush loose material
- Apply fungicidal wash to kill mould spores
- Allow 24-48 hours drying time
Step 4: Test moisture levels Use your moisture meter to establish baseline readings. Record these for later comparison.
Phase 2: Installing Your Chosen System
For DPM Installation:
Step 1: Fix the membrane
- Start from the bottom, overlapping joints by 150mm
- Use mechanical fixings every 300mm
- Ensure membrane extends 150mm beyond damp area
Step 2: Create an air gap Install 25mm battens to separate membrane from new wall finish. This prevents condensation buildup.
Step 3: Install new wall finish
- Fix plasterboard to battens
- Use moisture-resistant board in vulnerable areas
- Seal all joints with appropriate tape
For Tanking Systems:
Step 1: Apply primer Use manufacturer-specified primer to ensure proper adhesion.
Step 2: Install reinforcement
- Fix mesh at corners and joints
- Overlap mesh sections by 100mm
- Ensure mesh lies flat against wall
Step 3: Apply tanking slurry
- Work in 1-metre sections
- Apply with brush or spray
- Build up in thin coats rather than single thick application
Step 4: Install cavity drainage Some systems require drainage channels at floor level to manage water runoff.
Phase 3: Finishing and Monitoring
Step 1: Allow curing time Most systems need 7-14 days before applying finishes. Check manufacturer guidelines.
Step 2: Apply finishing coats
- Use breathable plaster systems
- Avoid vinyl wallpapers that trap moisture
- Choose moisture-resistant paints
Step 3: Monitor results Take moisture readings monthly for the first year. Properly installed systems should show steadily decreasing readings.
Choosing the Right Method for Your Situation
| Damp Type | Severity | Best Method | Typical Cost | DIY Suitable |
|---|---|---|---|---|
| Rising damp | Mild | DPM + replaster | £20-30/m² | Yes |
| Rising damp | Severe | Tanking system | £50-80/m² | No |
| Penetrating damp | Localised | Damp proof paint | £10-15/m² | Yes |
| Penetrating damp | Widespread | DPM membrane | £25-40/m² | Partial |
| Multiple damp types | Severe | Professional tanking | £60-100/m² | No |
Budget Considerations
DIY costs typically include:
- Materials: 60-70% of total cost
- Tools and equipment hire: 15-20%
- Disposal and preparation: 10-15%
Professional installation adds:
- Labour costs: £200-400 per day
- Insurance and guarantees
- Material markup: 20-40%
Plan for 20% contingency costs. Damp projects often reveal additional problems once work begins.
Common Mistakes to Avoid
Using Wrong Materials for Your Damp Type
Damp proof paint won’t solve severe rising damp. Tanking systems are overkill for minor condensation. Match your method to your specific problem.
Inadequate Preparation
Rushing preparation causes system failure. Remove all loose material, treat mould thoroughly, and ensure walls are as dry as possible before starting.
Ignoring Ventilation
Internal damp proofing can trap moisture in wall cavities. Always install adequate ventilation to prevent secondary problems.
Covering Up Without Treating
Painting over damp stains doesn’t solve anything. The moisture will return and damage your new decorations.
Poor Joint Sealing
Gaps in membranes or tanking systems let moisture through. Take time to seal all joints properly.
When to Call Professionals
Consider professional help when:
Damp covers large areas (over 10 square metres) Professional equipment and experience become cost-effective for bigger jobs.
Structural damage is evident Crumbling mortar, damaged bricks, or significant plaster failure need expert assessment.
Multiple treatment attempts have failed If DIY efforts haven’t worked, underlying issues may need professional diagnosis.
You’re dealing with listed buildings Conservation requirements need specialist knowledge and approved materials.
Health concerns arise Extensive mould growth or respiratory problems require immediate professional intervention.
Maintaining Your Damp Proof System
Regular Monitoring
Check moisture levels every 3-6 months using your moisture meter. Look for:
- Returning damp patches
- New staining or discolouration
- Musty odours
- Mould growth
Ventilation Management
Maintain adequate airflow around treated areas. Use extractor fans in bathrooms and kitchens. Open windows regularly to reduce humidity.
External Maintenance
Internal damp proofing works best when combined with proper external maintenance:
- Keep gutters clear and well-maintained
- Repair pointing and render cracks promptly
- Ensure ground levels don’t breach your DPC
Annual Checks
Inspect annually:
- Skirting boards for lifting or damage
- Wall surfaces for new stains
- Window and door seals
- Heating system efficiency
Advanced Solutions for Stubborn Damp
Positive Input Ventilation (PIV)
PIV systems continuously supply fresh, filtered air to reduce humidity levels throughout your home.
Cost: £400-800 installed Best for: Whole-house condensation control Benefits: Reduces damp risk across all rooms
Dehumidification Systems
Integrated dehumidifiers work alongside internal damp proofing to control moisture levels.
Running costs: £100-200 annually Capacity: Choose 10-20 litres daily extraction for typical homes Placement: Central locations with good airflow
Smart Monitoring
Modern moisture monitoring systems send alerts to your smartphone when humidity levels rise.
Features to look for:
- Multiple sensor locations
- Historical data tracking
- Alert thresholds you can set
- Integration with smart home systems
Cost Breakdown and Budgeting
Material Costs (DIY)
DPM membrane system:
- Membrane: £3-5 per square metre
- Battens: £2-3 per square metre
- Plasterboard: £8-12 per square metre
- Fixings and adhesive: £1-2 per square metre
Tanking system:
- Tanking slurry: £15-25 per square metre
- Mesh reinforcement: £2-3 per square metre
- Primer: £3-5 per square metre
- Finishing materials: £8-15 per square metre
Labour Costs (Professional)
Regional variations:
- London and South East: £300-500 per day
- Northern England: £200-350 per day
- Scotland and Wales: £180-320 per day
- Rural areas: £150-280 per day
Hidden Costs to Consider
- Temporary accommodation during work
- Furniture storage or protection
- Additional electrical work
- Replastering and redecorating
- Building control fees (if applicable)
Health and Safety Considerations
Personal Protection
Essential PPE:
- Dust masks (FFP3 rated for mould exposure)
- Safety goggles
- Nitrile gloves
- Steel-toed boots for major work
Chemical Safety
Many damp proofing products contain harmful chemicals. Always:
- Read safety data sheets
- Ensure adequate ventilation
- Store materials safely away from children
- Dispose of waste according to local regulations
Structural Safety
Stop work immediately if you discover:
- Significant structural damage
- Electrical hazards in damp areas
- Asbestos materials (common in pre-1980 buildings)
- Gas pipe corrosion
Troubleshooting Common Problems
Damp Returns After Treatment
Possible causes:
- External source not addressed
- Installation defects
- System not suitable for damp type
- Poor ventilation
Solutions:
- Reinspect external walls and drainage
- Check system integrity
- Consider additional ventilation
- Seek professional assessment
New Damp Appears Elsewhere
Internal damp proofing can redirect moisture to other areas. This is normal but manageable.
Prevention:
- Treat larger areas than just visible damp
- Improve overall ventilation
- Monitor adjacent walls
- Address external causes
Condensation Behind Membranes
Poor installation can trap moisture between your membrane and the wall.
Solutions:
- Ensure adequate air gaps
- Install vapour barriers correctly
- Improve ventilation
- Use breathable materials where possible
System Failure
If your damp proofing system fails within the first year:
- Check installation against manufacturer guidelines
- Test moisture levels systematically
- Document problems for insurance/warranty claims
- Consider upgrading to more robust system
Alternative and Complementary Solutions
Improving Natural Ventilation
Simple ventilation improvements often solve damp problems without major construction work.
Effective methods:
- Install trickle vents in windows
- Add air bricks to improve underfloor ventilation
- Create cross-ventilation pathways
- Remove furniture from external walls
Heating Improvements
Consistent, low-level heating reduces condensation and helps walls dry out.
Recommended approach:
- Maintain 18-21°C consistently
- Use programmable thermostats
- Avoid uneven heating patterns
- Consider underfloor heating in problem areas
Humidity Control
Managing indoor humidity levels supports any damp proofing system.
Target humidity: 40-60% relative humidity
Control methods:
- Use extractor fans during cooking and bathing
- Dry clothes outdoors when possible
- Use dehumidifiers during humid weather
- Ensure tumble dryers vent externally
Professional vs DIY: Making the Right Choice
DIY Suitability Assessment
You can handle DIY if:
- Damp area is under 5 square metres
- No structural damage is evident
- You have basic DIY skills
- Problem is clearly identified
Choose professionals when:
- Multiple walls are affected
- Structural repairs are needed
- Previous DIY attempts failed
- Building regulations approval required
Finding Qualified Contractors
Essential checks:
- Property Care Association membership
- Valid public liability insurance (minimum £2 million)
- Local authority trading standards approval
- Recent customer references
Questions to ask contractors:
- What guarantees do you provide?
- Are you familiar with this type of property?
- Can you provide a detailed written specification?
- What happens if the treatment fails?
Costs and Time Frames
Typical Project Timelines
Small room (10-15m² wall area):
- DIY membrane system: 3-5 days
- Professional tanking: 5-7 days
- Including drying and finishing: 2-3 weeks total
Large room (20-30m² wall area):
- DIY membrane system: 5-8 days
- Professional tanking: 8-12 days
- Including drying and finishing: 3-4 weeks total
Budget Planning
Total project costs (including materials, labour, and finishing):
| Room Size | DIY DPM | DIY Tanking | Professional |
|---|---|---|---|
| Small bathroom | £200-400 | £400-700 | £800-1,500 |
| Average bedroom | £400-800 | £800-1,400 | £1,500-2,800 |
| Large living room | £800-1,500 | £1,500-2,500 | £2,500-4,500 |
Add 20-30% for unexpected complications or additional treatments.
Legal and Regulatory Requirements
Building Regulations
Internal damp proofing usually doesn’t require building regulations approval, but check with your local authority if:
- You’re altering structural elements
- Installing new electrical circuits
- Changing room ventilation significantly
- Working on listed buildings
Insurance Implications
Inform your home insurance provider about damp problems and treatments. Some policies exclude damp damage, while others require professional treatment.
Landlord Responsibilities
If you’re a tenant, your landlord must address damp problems that affect health or safety. Document issues thoroughly and contact your local council’s environmental health department if problems persist.
Maintenance and Long-term Care
Annual Maintenance Schedule
Spring (March-May):
- Check external walls for winter damage
- Clear gutters and downpipes
- Test internal moisture levels
- Service mechanical ventilation
Summer (June-August):
- Monitor humidity during humid weather
- Check dehumidifier efficiency
- Inspect painted surfaces for early signs of moisture
Autumn (September-November):
- Prepare heating systems
- Check window and door seals
- Clear external drainage
- Test emergency ventilation
Winter (December-February):
- Monitor condensation levels
- Ensure consistent heating
- Check for ice damage to external walls
- Maintain adequate ventilation despite cold weather
Warning Signs to Watch For
Contact professionals immediately if you notice:
- Rapid return of damp patches
- New musty odours
- Mould growth despite treatment
- Structural movement or cracking
- Electrical problems in treated areas
Frequently Asked Questions
How long does internal damp proofing last?
Well-installed systems typically last 20-30 years. DPM systems may need maintenance after 15-20 years, while tanking systems can last longer with proper installation.
Can I damp proof just one wall?
Yes, but moisture may migrate to adjacent walls. Treat at least 500mm beyond visible damp boundaries for best results.
Will internal damp proofing stop all moisture problems?
Internal systems manage moisture reaching your living space but don’t stop water entering your walls. Combine with external maintenance for best results.
How do I know if my damp proofing is working?
Monitor moisture levels monthly. Readings should decrease steadily over 6-12 months. Visual improvements typically appear after 3-6 months.
Can I wallpaper over damp proofed walls?
Yes, but use breathable wallpapers and adhesives. Avoid vinyl wallpapers that can trap moisture.
What about guarantees and warranties?
Professional installations typically include 10-20 year guarantees. DIY materials often carry 5-10 year warranties. Keep all documentation and maintain systems according to instructions.
Is internal damp proofing suitable for all property types?
Most properties benefit from internal damp proofing, but listed buildings may need conservation officer approval. Timber-framed buildings require specialist consideration.
How do I deal with salt deposits?
Salt contamination from rising damp needs special treatment. Use salt-neutralising products before applying any damp proofing system, or salts will continue causing problems.
Summary and Next Steps
Internal damp proofing offers an effective solution for persistent moisture problems when external repairs aren’t feasible. Success depends on accurate problem diagnosis, choosing the appropriate method, and proper installation.
Key takeaways:
- Identify your specific damp type before choosing treatment
- Match the solution intensity to your problem severity
- Prepare thoroughly for long-lasting results
- Combine internal treatments with external maintenance
- Monitor results and maintain systems properly
Your next steps:
- Assess your damp problem using the methods outlined above
- Choose the most appropriate treatment system
- Gather materials and plan your project timeline
- Install your chosen system following manufacturer guidelines
- Monitor results and maintain the system long-term
Remember that internal damp proofing works best as part of a comprehensive moisture management strategy. Address external causes where possible, maintain adequate ventilation, and keep monitoring moisture levels even after successful treatment.
For complex problems or if you’re unsure about any aspect of the work, consult qualified professionals. The Property Care Association and British Standards Institution provide additional guidance on damp proofing standards and best practices.
With proper planning and execution, internal damp proofing can transform damp, unhealthy rooms into comfortable, dry living spaces that protect both your property value and your family’s health.