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What is Penetrating Damp?

Rain penetration through masonry (known as penetrating damp) is a common problem in buildings – particularly in the case of those of solid wall construction. The problem is also increasingly common in buildings of cavity wall construction where cavity wall insulation has been poorly installed or used in walls that are not suitable for cavity wall insulation. Other paths through which rain can cross through a cavity wall include incorrectly positioned wall ties and mortar obstructions in the cavity.

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Symptoms of Penetrating Damp

The most common visual symptom of rain penetration is damp patches on internal walls – often causing paint to flake or wallpaper to peel. However damp masonry caused by penetrating damp can also result in a wide range of other symptoms including:

  • Reduced thermal resistance of damp masonry – causing heat loss and condensation
  • Moss and mould growth
  • Frost damage
  • Rotting of embedded timbers
  • Disfiguring carbonate deposits

Traditional Measures for Preventing Penetrating Damp

A wide range of traditional measures are available to deal with the problem of rain penetration through walls. These include:

  • Cladding
  • External renders
  • Weatherproof paints and coatings
  • Tile or slate hanging
  • Timber boardings

Whilst all these solutions can be effective, they all have the disadvantage of changing the visual appearance of the building to which they are applied. For this reason an alternative approach is required in situations where the original appearance of brick or stone masonry needs to be maintained.

Treating Damp Walls With Stormdry

Stormdry Masonry Protection Cream and Stormdry Repointing Additive can be used to provide protection against penetrating damp without affecting the visual appearance of brickwork or stonework.

The application of Stormdry Masonry Protection Cream prevents the absorption of rainwater into porous building materials such as brick or sandstone whilst still allowing the passage of water vapour – i.e. the wall is still able to “breathe.” Because Stormdry Masonry Protection Cream penetrates deeply into common masonry substrates such as brick and stonework, it is able to resist rain penetration through shallow cracks. Nevertheless, all cracks in masonry visible at the time of application should be filled before the application of Stormdry.

Cracks in mortar and small shrinkage cracks at the interface between the mortar and brick/stone can provide a pathway through which rain can penetrate. For this reason, prior to the application of Stormdry Masonry Protection Cream any cracked or unsound mortar should be raked out and repointed using a suitable sand:lime or sand:cement mortar incorporating Stormdry Repointing Additive tooled to a “bucket handle” finish.

Additional Measures

Good building design and maintenance plays an important role in preventing rain penetration. For example, blocked downpipes and poor detailing can result in large amounts of rainwater coming to bear against a small section of wall. Any such defects should be identified and rectified.


Stormdry has been tested to EN ISO15148:2002 (E), demonstrating its effectiveness on concrete, mortar, brick, and sandstone:

Penetration Depth

Stormdry is able to penetrate more deeply into masonry than traditional liquid-applied masonry water repellents:

Stormdry's increased penetration depth provides a number of benefits including:

  • Increased life expectancy - unlike thin coatings, Stormdry's effectiveness will not be affected by the erosion of the masonry surface over time.
  • Improved crack-bridging ability - because Stormdry penetrates deeply into masonry, it will penetrate beyond the depth of small cracks.