Damp proofing is a vital process that protects your home from rising damp, penetrating damp, and condensation problems. If you’ve noticed peeling paint, musty smells, or damp patches creeping up your walls, you’re not alone — these are common signs of moisture problems in UK homes, especially older properties.
This guide explains how damp proofing is done, the different methods used, and answers common questions like “Can I do damp proofing myself?” and “Is damp proofing done inside or outside?”
Damp proofing is done by drilling holes along the mortar line, injecting a silicone-based chemical cream into the wall, and creating a waterproof barrier that prevents rising damp. The process includes four main steps:
- Assessment – Identify the type and extent of damp.
- Preparation – Remove plaster and clean exposed brickwork.
- Injection – Inject a chemical damp-proof course (DPC) 150mm above ground level.
- Replastering – Apply salt-resistant plaster before repainting once dry.
🧱 What Is Damp Proofing?
Damp proofing is the method used to stop moisture from entering walls or floors from the ground or external sources. The goal is to create a moisture-resistant barrier that prevents structural damage, mould, and health problems caused by damp air.
In modern homes, this is achieved by installing a damp-proof course (DPC) — a horizontal layer in the wall that stops moisture from rising. In older homes, this barrier may be missing or deteriorated, which is where chemical or physical damp proofing comes in.
Step-by-Step: How Damp Proofing Is Done
Let’s walk through the standard professional damp proofing process, typically used to treat rising damp — the most common type of damp that travels upward through walls by capillary action.
1. Assessment and Preparation
Every job begins with a damp survey.
A qualified specialist assesses the property using moisture meters and thermal imaging to identify where damp is present and what type it is — rising, penetrating, or condensation.
Once diagnosed:
- Contaminated plaster and paint are removed from the affected walls.
- The brickwork is exposed so the new damp-proofing system can bond effectively.
- The technician checks that the treatment line is at least 150mm above external ground level, ensuring it sits above any potential moisture zone.
2. Drilling the Wall
Next, small holes are drilled into the horizontal mortar joints at even intervals — usually 10–12mm in diameter, spaced around 100–120mm apart.
This is done internally or externally, depending on access and wall construction.
The holes create the channels for the damp-proofing cream to be injected.
3. Chemical Injection
A silicone-based damp-proof cream (the chemical DPC) is then injected into the holes using a specialised applicator.
Once inside the wall:
- The cream spreads through the mortar bed.
- It forms a water-repellent barrier that stops ground moisture from rising.
This barrier becomes permanent once cured, protecting the wall for decades.
4. Replastering and Finishing
After injection:
- The wall must dry naturally, which can take several weeks depending on severity.
- Once dry, the area is replastered with a salt-resistant render to stop any leftover ground salts from damaging new plaster.
- Finally, the wall can be redecorated — typically after 4–6 weeks.
This final step is crucial because salts from damp walls can ruin new paint if applied too soon.
Other Common Damp Proofing Methods
Not all damp issues are the same. Here’s a breakdown of other professional methods besides chemical injection.
1. Physical Damp-Proof Courses (DPCs)
In some cases — especially during renovations — a physical barrier is installed.
This may involve:
- Bitumen membranes,
- Engineering bricks, or
- Plastic DPC sheets.
These materials are placed within the wall or under floors to block moisture from the ground.
🧱 Used for: New builds or complete wall rebuilds.
⚠️ Downside: Disruptive and costly, but extremely long-lasting.
2. Electro-Osmotic Damp Proofing
This is a non-invasive electrical system used when drilling isn’t ideal.
It involves fitting copper wires and an earth connection into the wall.
When a small electric current is applied, it reverses the natural capillary action, pushing moisture back down into the ground.
⚙️ Used for: Heritage or solid stone walls.
💡 Benefit: Minimal mess; suitable for large buildings.
3. Membrane Systems (for Penetrating Damp)
If your walls are affected by external water penetration, professionals may install an internal waterproof membrane on the inside face of the wall.
These membranes:
- Create a continuous moisture barrier,
- Can be plastered or drylined over, and
- Often overlap a new chemical DPC for full protection.
🛡️ Used for: Basements, cellars, or external wall damp.
🔩 Also called: Cavity drain membrane systems.
🏠 Internal vs External Damp Proofing
Many homeowners ask: “Is damp proofing done inside or outside?”
The answer depends on where the moisture enters.
| Type of Damp | Typical Treatment Location | Description |
|---|---|---|
| Rising Damp | Internal or external | DPC injection line 150mm above ground |
| Penetrating Damp | External | Repointing, sealing cracks, adding membranes |
| Condensation | Internal | Improving ventilation and insulation |
In most UK homes, chemical DPC injection is done from the inside, followed by internal replastering. But for older solid-wall properties or severe ingress, external treatment may be needed too.
Can You Do Damp Proofing Yourself (DIY)?
You can buy DIY damp-proofing creams and attempt to treat small patches — especially for minor rising damp in single walls.
However, there are key risks:
- Incorrect drilling depth or spacing may make the barrier ineffective.
- Failing to remove salt-contaminated plaster means damp will reappear.
- Condensation or penetrating damp may be misdiagnosed, wasting time and money.
If you’re not sure what’s causing the damp, it’s best to get a professional damp survey before spending on materials.
Cost of Damp Proofing Internal Walls
Costs vary based on wall size, thickness, and severity.
Here’s an approximate guide for UK homeowners:
| Type of Treatment | Average Cost (per metre) | Notes |
|---|---|---|
| Chemical Injection DPC | £60 – £80 | Includes drilling and cream |
| Replastering with Salt-Resistant Render | £25 – £35 | Required after DPC |
| Membrane System | £70 – £120 | Used for basements |
| Electro-Osmotic DPC | £100+ | Specialist solution |
A full damp-proofing treatment for an average 3-bed house may cost between £800–£2,000, depending on condition and access.
🧱 How to Treat Damp Walls Internally
Here’s a simplified guide to treating damp walls inside your home:
- Identify the cause – Rising, penetrating, or condensation.
- Prepare the wall – Remove plaster, paint, or wallpaper.
- Drill and inject – Apply chemical cream into the mortar.
- Allow drying time – Usually several weeks.
- Replaster and redecorate – Use salt-resistant materials.
- Improve ventilation – Use extractor fans or dehumidifiers to prevent return.
How to Put a Damp-Proof Course in an Old House
Older homes often lack a DPC or have one made from slate or bitumen, which may have failed over time.
To retrofit a new DPC:
- A specialist drills and injects a chemical cream, as described above.
- In rare cases, bricks are carefully removed and replaced with a physical DPC layer, though this is usually done during major refurbishments.
Always consult a professional if your property is pre-1950s or built with solid walls.
Treating Damp Walls Before Painting
Never paint over damp patches — it only hides the problem temporarily.
Before painting:
- Make sure the wall is fully dry.
- Use a salt-resistant plaster or filler.
- Apply breathable paint (not vinyl-based) to allow moisture evaporation.
This ensures the finish lasts and prevents bubbling or peeling.
How to Damp-Proof a Wall from Inside
For walls that can’t be treated externally, professionals use internal wall systems such as:
- Chemical injection from the inside, or
- Waterproof membranes that act as internal tanking barriers.
These solutions are ideal for:
- Basement flats,
- Party walls, or
- Properties in terraced streets with no exterior access.
Summary: How Damp Proofing Is Done in the UK
| Stage | Description | Purpose |
|---|---|---|
| 1. Assessment | Identify damp type & severity | Plan correct treatment |
| 2. Preparation | Remove plaster, expose brick | Allow injection |
| 3. Drilling | Holes along mortar joint | Enable DPC injection |
| 4. Injection | Apply silicone cream | Form moisture barrier |
| 5. Drying | Wait several weeks | Let walls dry |
| 6. Replaster & Paint | Salt-resistant render | Restore wall appearance |
FAQ
How is damp proofing done?
By drilling into the mortar bed and injecting a water-repellent cream to block rising moisture.
Can I do damp proofing myself?
Small areas can be DIY-treated, but professional diagnosis ensures lasting results.
Can damp proofing be done without removing plaster?
Not effectively. Contaminated plaster must be removed to prevent salts from reappearing.
Is damp proofing done inside or outside?
Usually from the inside, though external treatment may be required for penetrating damp.
How long does damp proofing last?
correctly installed chemical DPC can last 20–30 years or more.
Can I do damp proofing myself?
DIY kits are available, but professional installation ensures correct drilling depth, spacing, and full barrier protection. Incorrect DIY damp proofing can fail quickly.
Can damp proofing be done without removing plaster?
Not effectively. Salt-contaminated plaster must be removed before injecting or the wall won’t dry properly.
Is damp proofing done inside or outside?
Usually done inside the property, but external walls may need additional sealing or membranes to stop penetrating damp.
How long does damp proofing last?
A professionally installed chemical DPC can last over 20 years if the treated wall remains structurally sound.
How much does damp proofing cost?
The average cost ranges between £60–£80 per metre for chemical DPC, plus replastering and finishing.
Get Help Now
Damp proofing is both a preventive and restorative process. Done correctly, it protects your home from structural damage, health risks, and costly repairs.
If you suspect rising or penetrating damp, don’t ignore the signs.
👉 Contact Damp and Mould Solutions Ltd for a professional damp survey, guaranteed treatments, and expert guidance on keeping your walls dry long-term.