Damp proofing for exterior walls

Damp is a common problem that can affect many properties. It can cause a wide range of issues, from cosmetic damage to health problems, and can be challenging to remove once it has taken hold. Damp proofing is the process of preventing damp from entering a property, and it’s essential to keep your home safe and comfortable. In this article, we’ll explore techniques and products used to damp proof the external walls of buildings.

What is damp proofing?

Damp proofing refers to the measures taken to prevent moisture from entering a property. These measures include sealing out water from the foundation, preventing water from entering through the roof and walls, and providing adequate ventilation to prevent condensation.

Why is damp proofing important?

Damp can cause a variety of problems, from cosmetic damage to structural problems. It can lead to unpleasant smells, mould growth, and even cause health issues. Damp can also attract pests, including insects and rodents, making the property less desirable to live in.

How do you know if you have a damp problem?

The signs of damp include:

  • Musty smells
  • Discoloured or peeling wallpaper
  • Damp patches on walls or ceilings
  • Mould growth
  • Wet or decaying woodwork

What causes damp?

Damp can be caused by a range of factors, including:

  • Poor ventilation
  • Leaking pipes or gutters
  • Condensation
  • Rising damp from the ground
  • Penetrating damp from rainwater
  • Poor insulation

What are the techniques and products used to damp proof external walls?

Damp proofing external walls is essential to prevent moisture from penetrating into a building. The following techniques and products can be used to damp proof external walls:

1. Damp-proof course (DPC)

A damp proof course (DPC) is a layer of material that is installed in a wall to prevent moisture from rising through the masonry. The DPC can be made from a range of materials, including:

  • Plastic
  • Bitumen felt
  • Metal
  • Chemical compounds

The DPC is installed at a specific height in the wall, usually around 150mm above ground level. This ensures that the masonry above the DPC remains dry, preventing dampness from rising up through the wall.

2. External render

External render is a layer of material that is applied to the outside of a wall to provide a protective layer against the elements. It can also act as a barrier against moisture, preventing water from penetrating into the wall. The render can be made from a range of materials, including:

  • Lime
  • Cement
  • Acrylic

External render must be correctly applied to ensure that it provides an effective barrier against moisture. It should also be sealed to prevent water from seeping into the masonry.

3. Cavity wall insulation

Cavity wall insulation involves filling the gap between the inner and outer walls of a property with insulating material. This can help to reduce heat loss and improve energy efficiency in the home. Cavity wall insulation can also help to prevent damp by reducing the amount of cold air that enters the property.

4. Waterproof coatings

Waterproof coatings, such as siloxane coatings, can be applied to external walls to create a barrier against water. These coatings are transparent, meaning they don’t affect the appearance of the property and can also be applied to older buildings. However, waterproof coatings must be applied correctly to ensure they work effectively.

5. Drainage

Drainage is essential for preventing water from pooling around the foundations of a property. Proper drainage can be achieved through the installation of appropriate drainage channels and gutters, and by ensuring that the land around the property is graded to slope away from the building.


Damp proofing external walls is essential for maintaining a dry and healthy property. The techniques and products outlined in this article can help to prevent damp from entering a building and causing problems. If you suspect that your property has a damp problem, it’s essential to consult a professional who will be able to identify the cause of the damp and suggest the appropriate solution. By taking preventative measures, you can protect your property from damage and maintain a safe and comfortable environment for your family.

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