How to Fix Rising Damp: A Comprehensive Guide

Rising damp is a persistent problem for many homeowners, particularly in older properties where damp-proofing measures may be inadequate or have deteriorated over time. If left untreated, it can cause significant structural damage, health issues, and a reduction in property value. This comprehensive guide explains how to fix rising damp in a house, examines what causes rising damp in internal walls, explores how to treat damp walls internally, and provides solutions for how to treat rising damp in an old house.

Understanding Rising Damp

Rising damp occurs when moisture from the ground travels upward through porous building materials, such as bricks and mortar, via capillary action. This moisture can carry salts and other contaminants, which crystallize and cause further damage when they reach the surface.

What Causes Rising Damp in Internal Walls?

There are several factors that contribute to rising damp in a house:

1. Failure or Absence of a Damp-Proof Course (DPC)
   • A DPC is a protective barrier installed near the base of walls to prevent moisture from rising.
   • In older homes, this barrier may be missing or deteriorated, allowing damp to seep in.
2. Porous Building Materials
   • Bricks, stone, and mortar naturally absorb moisture. If these materials lack an effective damp-proof layer, moisture can travel through them easily.
3. High Groundwater Levels
   • If a house is built in an area with a high water table, moisture is more likely to be drawn up through the walls.
4. Blocked or Defective Drainage Systems
   • Poor drainage around the house can lead to water accumulating near the walls, increasing the risk of rising damp.
5. Bridging of the DPC
   • If external ground levels (such as raised patios, flower beds, or paving) are higher than the DPC level, moisture can bypass the protective barrier and enter the walls.
6. Leaking Pipes or Gutters
   • Persistent leaks can create damp conditions that encourage rising moisture within walls.

Identifying Signs of Rising Damp

Detecting rising damp early can prevent costly repairs. The most common symptoms include:

• Tide Marks & Staining: Moisture stains or discolouration appearing up to 1 metre above the ground level on internal walls.
• Peeling Paint & Wallpaper: Moisture weakens adhesives, causing wallpaper to peel or bubble.
• Salt Efflorescence: White, powdery deposits appear as moisture evaporates, leaving behind salts.
• Black Mould Growth: Persistent damp conditions encourage mould, which can lead to respiratory issues.
• Deteriorating Plaster & Crumbling Skirting Boards: Plaster becomes soft and powdery, and wooden fixtures may rot.
• Damp Odours: A musty smell often indicates excessive moisture.

How to Fix Rising Damp in a House

Fixing rising damp requires a combination of repairing structural deficiencies, improving ventilation, and treating walls to prevent further moisture penetration.

Step 1: Diagnose the Problem

Before beginning treatment, it’s essential to confirm that the damp issue is caused by rising damp rather than condensation or penetrating damp. A professional damp survey can provide an accurate assessment.

Step 2: Repair or Install a Damp-Proof Course (DPC)

If the damp-proof course is missing or has failed, it needs to be repaired or replaced.

1. Chemical Injection DPC

• A damp-proofing cream is injected into drilled holes along the mortar joint to form a new waterproof barrier.
• This method is cost-effective and minimally invasive, making it a popular choice for modern homes.
• Cost: £500 – £2,000 depending on property size.

2. Physical DPC Installation

• A new damp-proof membrane is inserted into the brickwork.
• This method is more expensive and invasive but is a permanent solution.
• Cost: £3,000 – £6,000 for a full property installation.

Step 3: Improve Drainage & Ground Levels

• Ensure that drainpipes, gutters, and downspouts are directing water away from the house.
• Lower external ground levels if they are higher than the DPC.
• Install gravel trenches or French drains around the property to redirect water away from the walls.

Step 4: Internal Wall Treatment

Once the moisture source is addressed, the internal walls need treatment to remove damage and prevent further issues.

1. Remove Contaminated Plaster

• Plaster that has absorbed moisture and salts must be stripped back to at least 1 metre above the visible damp line.
• Cost: £20 – £40 per square metre for removal and replacement.

2. Apply a Salt-Resistant Render

• Replaster walls using a salt-resistant cement-based render.
• Avoid using gypsum-based plaster, as it is prone to absorbing moisture.

3. Use Breathable Paints

• Standard emulsion and vinyl-based paints can trap moisture.
• Instead, use lime-based paints or mineral paints, which allow walls to breathe.

How to Treat Damp Walls Internally

In some cases, treating damp walls internally may be necessary, especially when external solutions are impractical.

1. Surface Treatments

• Anti-Mould Paints & Sealants: These can provide temporary relief but do not address the underlying damp issue.
• Damp-Proof Membranes: These are installed over damp walls before replastering to prevent further moisture penetration.

2. Dry Lining

• Moisture-Resistant Plasterboard: Installed over damp walls to create a barrier.
• Cons: This method does not fix the damp problem but rather conceals it, making it a short-term solution.

How to Treat Rising Damp in an Old House

Older properties require special considerations to prevent damage to historic features.

1. Avoid Modern Sealants

• Cement-based renders and waterproof paints trap moisture and worsen damp problems.
• Instead, opt for lime-based plasters that allow moisture to evaporate naturally.

2. Improve Ventilation

• Older homes often lack modern ventilation systems, leading to increased moisture retention.
• Use air bricks, extractor fans, and dehumidifiers to promote airflow.

3. Heritage-Sensitive Damp-Proofing

• Consult a building conservation specialist before making alterations to listed or historic properties.

Preventing Rising Damp in the Future

Taking preventative measures can stop rising damp from returning:

✔ Maintain Gutters & Drainage: Regularly clean gutters and ensure downspouts are directing water away from the house.
✔ Lower External Ground Levels: Keep flower beds, patios, and soil at least 15 cm below the DPC line.
✔ Use Breathable Materials: Lime-based plasters and paints allow moisture to escape naturally.
✔ Regular Home Inspections: Periodically check for early signs of damp and take action promptly.

Conclusion

Rising damp can cause serious damage to both the structure of a house and the health of its occupants if left untreated. By understanding what causes rising damp in internal walls, homeowners can take the necessary steps to treat damp walls internally and fix rising damp in an old house.

Key takeaways:

• Identify early signs such as tide marks, salt efflorescence, and deteriorating plaster.
• Address the root cause by installing or repairing a damp-proof course (DPC).
• Use drainage improvements and internal wall treatments to mitigate damage.
• Consider breathable materials for older homes to prevent moisture retention.

Taking these steps will protect your home, improve indoor air quality, and prevent long-term structural damage.

Find local Damp Proofing companies

Sources

• Wikipedia – Damp Proofing