• August 1, 2025
• Nyla Thompson

How to Treat Damp Walls Internally and Get Rid of Rising Damp for Good

Damp walls are one of those household problems that never stay hidden for long. Maybe it’s peeling paint, a musty smell in the corner of your bedroom, or salty patches showing through the plaster. Whatever the sign, damp is more than just an eyesore—it can lead to mould, poor air quality, and even structural issues if ignored.

The good news? Most damp problems can be fixed. Whether you’re dealing with rising damp, penetrating damp, or just stubborn condensation, this guide walks you through how to identify the cause, choose the right treatment, and stop the damp from coming back.

Understanding Damp in Internal Walls

Not all damp is the same. Before you can fix the issue, it helps to know what type of damp you’re dealing with. Here are the three most common types found in UK homes:

1. Rising Damp

This happens when moisture from the ground is drawn up into your walls, often due to a missing or failed damp proof course (DPC). You’ll usually notice tide marks, flaky plaster, or powdery white salts along the bottom of walls.

2. Penetrating Damp

Caused by water entering through the outside—think cracks in the render, broken gutters, or leaky roofs. It tends to appear in isolated spots and can spread quickly if not addressed.

3. Condensation

Usually caused by poor ventilation, condensation is the most common form of damp. It often shows up as black mould in corners, behind furniture, or around windows.

Knowing the difference matters. Treating rising damp with anti-mould spray won’t solve the problem—just like installing a dehumidifier won’t stop water getting in from outside.

Causes of Dampness in Internal Walls

To stop damp properly, you need to know what’s causing it in the first place. Here are the most common reasons your walls might be getting wet on the inside:

Rising Damp Causes

• Missing or broken damp proof course (DPC): Older homes often have no DPC or one that’s failed over time.
• Bridging: If soil, paving, or render covers the DPC line, moisture can bypass it.
• Porous bricks or mortar: Over time, bricks can soak up ground moisture like a sponge.
• No air bricks or poor subfloor ventilation: This prevents trapped moisture under floors from escaping.

Penetrating Damp Causes

• Cracked render or damaged pointing: These let rainwater seep in through external walls.
• Blocked or broken gutters and downpipes: Water running down walls can quickly find its way inside.
• Leaky roofs or flashing: Especially in upstairs rooms or loft conversions.
• Old or unsealed window frames: Water gets in around the edges and soaks into internal plaster.

Condensation and Internal Moisture

• Poor airflow: Bathrooms, kitchens, and bedrooms without proper ventilation are common problem areas.
• Drying clothes indoors: This adds extra moisture into the air with nowhere to go.
• Cold surfaces: Condensation often forms where warm moist air hits a cold wall.

If you’re seeing wet patches in corners, along skirting boards, or behind furniture—chances are one of the above is to blame. And sometimes, it’s a mix of more than one.

How to Diagnose the Type of Damp in Your Wall

Before you start patching or painting, it’s worth taking a moment to confirm what kind of damp you’re dealing with. Treating the wrong type can be a waste of time—and money.

👁️ Look at the Symptoms

Here’s what to check for:

• Rising Damp:
  • Usually starts at the bottom of ground-floor walls
  • Salt marks (white, powdery deposits)
  • Peeling paint or wallpaper near skirting boards
  • Consistent height across affected walls
• Penetrating Damp:
  • Random patches, not always near the floor
  • More likely on one side of the house (usually where rain hits)
  • Gets worse in wet weather
  • May be near windows, chimneys, or around old repairs
• Condensation:
  • Black mould in corners or behind furniture
  • Often in rooms with poor airflow (bedrooms, bathrooms, kitchens)
  • Usually worse in winter or after showers/cooking
  • Windows may also steam up regularly

🔧 Use a Moisture Meter (Optional)

If you want to be sure, a simple moisture meter (available at DIY stores) can help you see if moisture is rising from the ground or seeping in at one point. It’s not perfect, but it gives you a decent reading before calling a pro.

👷 When to Call a Specialist

If you’re unsure or if the damp keeps returning, it’s best to get a damp survey from a qualified company. They’ll identify the source and recommend a proper fix—especially useful if you’re buying or selling a home.

How to Treat Damp Walls Internally (DIY & Professional Methods)

Once you’ve identified the type of damp affecting your walls, it’s time to fix it properly. The key is not just to cover the symptoms—but to stop the moisture at its source. Let’s break down how to treat each type of damp with practical steps, whether you’re doing it yourself or calling in the pros.

🧱 How to Treat Rising Damp (Ground Moisture Soaking Up)

Rising damp is usually caused by a failed or missing damp-proof course (DPC). It starts from the ground up, creeping up your internal walls and leaving behind salts, stains, and flaky paint. Here’s how to fix it:

1. Damp-Proof Course Injection (DPC Injection)

This is the most common permanent fix for rising damp.

DIY Steps:

• Drill holes horizontally along the bottom of the internal wall (about 150mm from floor level, spaced 100–120mm apart).
• Inject a chemical DPC cream or fluid—Dryzone, Permaguard, or No More Damp are commonly used.
• Let it cure for 24–48 hours before plastering.

Professional Help:

• Pros will do the same but with specialist tools and better accuracy, often including a moisture survey and guarantee.

Cost: DIY kits cost £50–£100. Professional DPC injection is usually £70–£120 per metre, including removal and replastering.

2. Hack Off and Replaster Salt-Damaged Areas

Once the DPC is done, the wall still needs repair. Salt-contaminated plaster will continue attracting moisture, even if the wall is now dry.

Steps:

• Remove plaster up to 1 metre above the highest damp line.
• Use salt-resistant render or renovating plaster (e.g., Limelite, Dryzone Renovation Plaster).
• Allow the wall to dry thoroughly before painting.

3. Install a Damp-Proof Membrane (DPM)

This is a plastic sheet or mesh-backed membrane that creates a physical barrier behind the new wall finish.

Best for:

• Very old walls, heavy damp areas, or when insulation is also being added.

🌧️ How to Treat Penetrating Damp (Leaks or Rainwater Coming Through)

Penetrating damp comes from outside water finding its way in—through bricks, render, roof leaks, or broken pipes.

1. Fix External Issues First

• Check brickwork and pointing. Repoint gaps with mortar if needed.
• Repair render or cracks. Use exterior filler or a render patch kit.
• Clear gutters and downpipes. Overflowing water often leads to soaked internal walls.
• Inspect roof tiles and flashing. A roofer may be needed if damage is found.

2. Seal Exposed Areas Internally

Once the outside is sorted, you can treat the inside:

• Apply a breathable waterproofing cream (like Stormdry) directly to internal brick or blockwork.
• Use a damp-proof internal sealant or paint (e.g., Ronseal Anti-Damp Paint or Zinsser Watertite) as a barrier layer before re-painting.

3. Add Insulation Where Needed

If the wall is constantly cold, internal insulation such as thermal plasterboard or insulating lining paper can reduce cold bridging and damp reappearance.

💨 How to Treat Condensation Damp (Surface-Level Moisture)

Condensation forms when warm, moist air hits a cold surface. It’s common in homes with poor ventilation or lots of indoor drying.

1. Improve Airflow

• Fit extractor fans in kitchens and bathrooms.
• Use trickle vents or open windows for short periods daily.
• Avoid blocking air bricks or wall vents.

2. Use a Dehumidifier

Running a dehumidifier in affected rooms helps pull moisture from the air. Ideal for bedrooms, loft conversions, or corners that stay cold.

3. Clean and Treat Mould

• Wipe off mould with a mould-killing spray (avoid just using bleach—it doesn’t kill spores).
• Once clean, apply anti-mould paint such as Zinsser Perma-White or Ronseal Anti-Mould.
• Repaint with a breathable emulsion, not vinyl-based paint which traps moisture.

4. Insulate Problem Walls

If one wall gets particularly cold, try:

• Thermal lining paper (easy DIY)
• Insulated plasterboard (requires more work but better long-term)
• Reflective foil wallpaper behind radiators

⚠️ Common Mistakes to Avoid

• Don’t paint over damp without fixing the cause—it will peel, crack, or bubble again.
• Don’t block air bricks—they’re there for ventilation.
• Avoid using cement renders on old stone or brick walls—it can trap moisture.

How to Dry Out Damp Walls Safely

Once you’ve stopped the source of damp, the wall still needs time—and the right conditions—to dry out fully. Rushing into painting or decorating too soon can trap moisture and cause more problems later.

Here’s how to dry out damp walls properly, step by step.

🧼 1. Remove Any Damp Materials First

If your wall has peeling wallpaper, bubbling paint, or mouldy plaster, strip it back before drying. Leaving damaged finishes in place can trap moisture underneath and slow down the drying process.

• Wallpaper: Strip off entirely and dispose.
• Paint: Scrape away any flaking or blistered areas.
• Mould: Wipe down with a fungicidal wash or white vinegar + water (not just bleach).

💨 2. Improve Ventilation

Moisture needs somewhere to go. Open windows regularly and keep air flowing.

• Cross-ventilate: Open windows on opposite sides of the room, even for 20 minutes at a time.
• Use extractor fans: Especially in bathrooms, kitchens, or laundry rooms.
• Leave internal doors open: This helps air circulate throughout the home.

If your home is well-sealed or in winter months, natural ventilation might not be enough. That’s where the next step comes in.

🌬️ 3. Use Heat and Air Movement Together

You don’t need to blast heat—but a consistent temperature helps evaporation. The trick is combining warmth with airflow.

• Use a fan heater or oil radiator to warm the space
• Use a desk fan or oscillating fan to move air gently across the wall
• Avoid directing heat at the wall itself—this can cause cracking or superficial drying

For best results, keep the room at 18–20°C (64–68°F) for several days.

💧 4. Add a Dehumidifier

A good-quality dehumidifier speeds things up without risking damage. It pulls excess moisture from the air, which encourages more evaporation from the wall surface.

• Place it near the damp wall, but not directly against it
• Empty the tank regularly or use a model with a drain hose
• Run it for several hours a day, especially in closed rooms

For deeper or older damp, you might need to run a dehumidifier for a few weeks.

⏳ 5. Be Patient (And Check Moisture Before Decorating)

Even after treatment, damp walls can take several weeks to fully dry out—especially solid brick or stone walls with no cavity. A simple moisture meter (under £30) can help you track progress.

• Aim for readings under 15% moisture content before applying paint or wallpaper
• Don’t rush into sealing or decorating, or you’ll trap moisture and start the cycle again

🔧 Optional: Use a Drying Aid or Salt Neutraliser

If rising damp was the issue, and white powdery salts keep coming through:

• Use a salt neutraliser (e.g., Dryzone Salt Inhibitor) before replastering
• Or apply a renovating plaster designed for damp environments

Dealing with Damp in Specific Areas

Not all damp shows up the same way in every part of your home. Whether it’s the bedroom, bathroom, basement, or a shared wall, each space comes with its own quirks. Here’s how to handle damp in the most common problem spots.

🛏️ Bedroom Walls (Especially Cold Corners)

Damp in bedrooms often appears as mould in the corners, behind furniture, or on the ceiling. This is usually due to poor airflow or hidden condensation.

What to do:

• Leave a gap between furniture and external walls so air can move.
• Use a thermal lining paper to reduce cold wall surfaces.
• Run a dehumidifier overnight if windows fog up in the morning.
• Improve airflow with trickle vents or a small extractor fan.

💡 Pro tip: If you dry laundry in your bedroom, always keep a window cracked open—it’s a common source of hidden condensation.

🛁 Bathroom & Kitchen Walls

These rooms naturally deal with steam, but when it clings to walls and ceilings, it can cause peeling paint, black spots, and even structural damage if left untreated.

What to do:

• Upgrade extractor fans: Aim for at least 15 litres/second capacity in bathrooms.
• Wipe down wet surfaces daily.
• Use mould-resistant paint and sealant.
• Install a humidity sensor fan that runs automatically when moisture levels rise.

🧱 Shared Walls (Party Walls)

If you’re in a terrace or semi-detached property and you spot damp along a shared wall, check both sides of the property.

What to do:

• Check for leaks or blocked gutters on your neighbour’s side.
• Apply breathable render or tanking paint if water ingress is suspected.
• Consult a surveyor if the cause isn’t obvious—shared wall issues can get complex.

🏚️ Basements & Cellars

Below-ground rooms are especially prone to rising and penetrating damp. Waterproofing here is a bigger job but worth doing right.

What to do:

• Install a cavity drain membrane system if converting the space.
• Use sump pumps to control groundwater in flood-prone zones.
• Apply tanking slurry to internal walls as a temporary fix.

📉 Note: Basement damp fixes often cost more—budget anywhere from £1,500–£5,000 depending on the size and method.

Signs You Need Professional Damp Treatment

Some damp issues are easy DIY wins. But when damp keeps coming back, spreads fast, or affects the structure of your home, it’s time to call in the pros. Here’s how to know when it’s beyond a simple fix.

🟠 1. Damp Patches Keep Reappearing

If you’ve cleaned the mould, repainted, and improved ventilation—but stains still return to the same spot—there’s likely a deeper issue like rising damp or penetrating moisture from outside. No amount of airing out will solve this without proper treatment.

🟠 2. Strong Musty Smell You Can’t Get Rid Of

That stale, earthy smell is often trapped within walls or under floors. It usually means moisture has penetrated materials like timber, plaster, or insulation. A surveyor can assess how far it’s spread using a moisture meter or thermal imaging.

🟠 3. Bubbling Paint or Plaster

If your plaster starts bubbling or flaking, or paint is blistering off in patches, it’s often a sign of salt migration from rising damp. This isn’t just cosmetic—it points to water travelling up from ground level and leaving mineral deposits.

🟠 4. Timber Rot or Floorboard Warping

Rising damp doesn’t just affect walls. It can damage joists, skirting boards, and floorboards. Soft or bouncy floors, especially near external walls, could be a red flag for wet rot or even dry rot, which spreads silently behind the scenes.

🟠 5. No Obvious Source, but the Damp Persists

If there’s no visible leak, no condensation problem, and no blocked gutter, but the wall still feels cold, damp, or shows signs of staining—it’s time for a full damp survey. Professionals use tools the average homeowner can’t access, including:

• Calcium carbide tests
• Thermal cameras
• Salt analysis
• Cavity inspection

🔍 In the UK, a PCA-qualified surveyor or a TrustMark-registered damp specialist is usually your safest bet.

Types of Damp Treatments (And When to Use Each)

Different types of damp need different fixes. Slapping on anti-mould paint won’t work if the issue is structural, and drilling for a DPC won’t help if the cause is condensation. Here’s how to match the treatment to the problem.

🧱 Rising Damp Treatment

Rising damp occurs when moisture travels up from the ground into the walls. It’s common in older houses with missing or damaged damp proof courses (DPC).

Treatment options:

• Chemical DPC injection: Holes are drilled into the brickwork and filled with a water-repelling cream or fluid. Cost: ~£70–£120 per metre.
• Damp-proof plaster/render: Used after injection to prevent salts and residual moisture from damaging the finish.
• Installing a new DPC (physical barrier): Rare but possible in extreme cases—much more invasive and expensive.

📌 Best for: Ground-floor walls, especially in Victorian or Edwardian homes.

🌧️ Penetrating Damp Treatment

This happens when water gets in through cracks, porous bricks, broken render, or faulty pointing.

Treatment options:

• Exterior wall repairs: Repointing bricks, sealing cracks, or applying breathable render.
• Masonry cream: A clear silicone-based cream applied to the outside brick to prevent rain from soaking in.
• Repairing roof/gutter leaks: Often the culprit behind sudden wall stains or soaked patches.

📌 Best for: External-facing walls, chimney breasts, or areas near windows.

💨 Condensation Treatment

Condensation-related damp usually shows up as black mould on corners, ceilings, and windows—caused by daily activities like cooking, washing, and drying clothes indoors.

Treatment options:

• Improving ventilation: Install extractor fans in bathrooms and kitchens or add trickle vents to windows.
• Use of anti-condensation paint: Helps prevent mould growth on vulnerable walls.
• Positive Input Ventilation (PIV) systems: Pushes fresh, filtered air into your home to reduce indoor humidity.

📌 Best for: Bedrooms, bathrooms, and poorly ventilated spaces.

🛠️ Tanking Slurry

Tanking is used to create a waterproof seal on the inside of a wall—typically in basements or below-ground spaces.

Treatment process:

• Brush-on slurry applied directly to masonry
• Usually covered with plasterboard or dot-and-dab finish
• May require mechanical ventilation if the room is below ground

📌 Best for: Cellars, utility rooms, and conversion projects below ground level.

DIY Damp Fixes That Actually Work

Some damp problems don’t need a builder, a surveyor, or a £500 quote. If you catch it early and act smart, you can fix—or at least manage—minor damp issues on your own. Here’s what works and what’s just a waste of time.

🧽 1. For Condensation and Mould: Ventilation + Cleaning

• Open windows daily (yes, even in winter).
• Use an extractor fan when cooking or showering.
• Wipe windows and sills each morning in cold months.
• Clean mould with white vinegar or mould spray—avoid bleach unless it’s specifically made for mould.

🛠️ Tip: Add a dehumidifier in high-risk rooms like bedrooms or bathrooms. Even a basic one from B&Q or Argos can reduce moisture dramatically.

🧱 2. For Penetrating Damp: Seal What You Can

If water’s getting in from outside:

• Check gutters and downpipes: Clear leaves, fix cracks, and make sure water flows away from your walls.
• Use masonry sealer or waterproofing cream on exposed brick.
• Seal cracks with exterior-grade filler or breathable render patch.

🛠️ Tip: Don’t use silicone indoors to fix internal cracks where damp is visible—it can trap moisture and make things worse.

🧼 3. For Small Patches of Rising Damp: Temporary Help

DIY won’t permanently stop rising damp, but you can slow its progress:

• Remove skirting boards and let walls dry before repainting.
• Apply a salt-neutralising primer after cleaning flaky paint or plaster.
• Use a damp-resistant lining paper as a short-term wall covering (especially if you’re renting and can’t renovate).

🛠️ Warning: If the damp comes back quickly or spreads, stop here and get a proper damp survey.

Common Mistakes to Avoid When Dealing With Damp

Trying to fix damp without getting to the root cause is like painting over rust. It might look better for a while, but the problem’s still there—and it’ll be back. Here’s what you don’t want to do.

❌ Painting Over Damp Patches

Paint won’t block moisture. If you slap emulsion or even anti-mould paint over a damp patch, it’ll bubble, peel, and eventually go brown or black. Always treat the damp first. If it’s still wet to the touch — stop.

❌ Using the Wrong Sealant or Filler

Silicone and generic wall fillers are not damp-proofing solutions. They can trap moisture inside the wall and make things worse over time. Always use breathable materials — especially for internal solid walls.

❌ Blocking Air Vents or Chimneys

Old homes need to breathe. Blocking off vents or stuffing a chimney to stop draughts might seem like a good idea until damp and mould start creeping in. Use vent covers or air bricks instead to allow controlled airflow.

❌ Ignoring External Issues

Damp on the inside often starts on the outside. Broken gutters, cracked rendering, or soil touching the damp course can lead to serious problems. Walk around your house in the rain — where does the water go? That’s your clue.

❌ Skipping the Damp Survey

If you’re seeing long-standing damp, bubbling plaster, or that musty “wet dog” smell — it’s worth paying for a proper survey. You don’t need to go with the first damp proofing company you find on Google. Look for someone independent, ideally certified by the Property Care Association (PCA) in the UK.

When to Call a Professional (And What It’ll Cost)

Not every damp issue needs a pro—but if you’ve tried the DIY fixes and things still feel musty, cold, or wet, it’s time to bring in backup.

🏚️ Signs You Need a Specialist

• Rising damp spreading across multiple walls
• Black mould keeps returning, even after cleaning and ventilating
• You’ve got damp on internal party walls (not just outside walls)
• The room smells damp, even when dry
• Plaster is crumbling or soft
• You’re about to buy/sell a house with visible damp patches

If any of these sound familiar, don’t guess. You’ll waste money. Get a proper diagnosis.

💷 What Does Professional Damp Treatment Cost in the UK?

Here’s what you can expect to pay:

• Damp survey: £150 to £400 (some companies offer it free if you use them for the work)
• Chemical DPC injection: £60–£120 per metre (plus plastering)
• Full internal damp proofing (inc. re-plastering): £1,000–£4,000 depending on the size of the area
• Basement tanking or waterproofing: £3,000–£12,000 for large areas
• Penetrating damp repairs (pointing, render fixes, etc.): £250–£1,500 depending on damage

🛠️ Tip: Always ask for a detailed quote and check if the company is PCA-registered or backed by an insurance guarantee. That way, you’re protected if the damp returns.

Want a more detailed breakdown with real UK price ranges? Check out this full damp proofing cost guide for a room-by-room comparison.

How to Keep Damp From Coming Back (Long-Term Prevention)

Fixing damp once is great. But keeping it from coming back? That’s the real win. Here’s how to stay ahead of it in the long run—especially in older UK homes where damp loves to sneak back in.

Keep Air Moving

• Ventilate every day. Open windows for 15–30 minutes, especially after showers or cooking.
• Use trickle vents, extractor fans, or even wall vents in sealed-up homes.
• Keep furniture slightly away from external walls—air needs room to move.

Maintain External Defences

• Clean and inspect gutters and downpipes twice a year.
• Repoint brickwork or patch render cracks before water gets in.
• Make sure garden soil or decking doesn’t cover your damp proof course.

Stay on Top of Condensation

• Invest in a good dehumidifier for winter (especially in bedrooms).
• Avoid drying clothes indoors unless windows are open or a fan is running.
• Use bathroom and kitchen fans every time, and leave them on for 10 minutes after.

Inspect Annually

Check walls, skirting boards, and window frames once or twice a year. If you spot peeling paint, damp patches, or bubbling plaster—don’t wait. Small issues become big bills when ignored.

Know When to Re-treat

If your home had rising damp treated more than 20 years ago, it might need attention again. Modern DPC injections last a long time—but not forever.