Southern Timber & Damp
0800 030 2121
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Damp Proofing Experts

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Damp Proofing - Rising Damp

What is it and how can we help?

All masonry structures are in one way or another in contact with the ground below them. Therefore the moisture content of the substrate can rise by capillary action into porous materials such as stone, brick or mortar. The most common route for Rising Damp is through and via the mortar joints and in older properties generally built before 1890, lime mortar was in widespread use. The usage of cement has been slowly replacing lime in modern build but most pre 2nd World War buildings continued to use lime as a standard building medium. The lime acts as a method of damp extraction from a structure and the science and balance of older house construction allowed the moisture to evaporate naturally via the lime plaster to the inside of the walls.

However, when this construction of lime plaster and mortar is intererfered with by the use of modern decorations and building materials (and in particular buildings that have been repointed in cement) the build up of ground salts will slowly undermine the integrity of the internal plaster finishes and can give rise to the permanent presence of Rising Damp. The contaminated plaster acts as a type of blotting paper over the mortar joints and the absorbed moisture will spread to form the band of dampness and typical tide mark associated with Rising Damp. The Ground Salts (Nitrates and Chlorides) will crystallise and turn into a solution within the plaster to form a permanently hygroscopic surface to attract further moisture from within the structure and to attract any Condensation from within the living environment. Condensation is a by-product of modern living and life style and the occurrence of Condensation within homes is escalating almost daily. Therefore it is usual to recommend a Damp Proofing Replastering at the same time as overall Damp proofing Treatment.

The purpose and aim of an effective Damp proof Course is to protect a structure from moisture rising from the ground by introducing a non porous material. The Public Health Acts of the last quarter of the 19th Century made the installation of a Damp proof Course a building regulation. During building works, non porous materials can be incorporated into the construction. If a Damp proof Course is installed into an older building in conjunction with the removal of the contaminated plaster from the interior walls and a replacement Damp proof Render, the combination will more than satisfy the dry environment required for a modern day living standard.

A Damp Proof Course has included such materials as lead, slate, bituminous material, plastic Damp proof Roll and double and staggered engineering bricks. However, over the decades, lead becomes porous, bitumen becomes brittle and plastic can deteriorate or perish. Settlement of buildings can also cause such materials to break down and become less effective.

In the 1990's Trading Standards tested samples of plastic Damp proof Course materials and found that a high proportion were defective even before the material was used. The effectiveness of a Damp proof Course can be further hampered by careless handling of the materials on site and during the installation process.

The Remedial Damp Proofing process and recommendations are to inject a silicone based product into the mortar joints to form an effective barrier to line the pores of the masonry which will negate porosity.

Products used for the injection of a Chemical Damp proof Course will depend on the type of wall and the materials used in the construction. They will include the following:-

  • Silicone Fluid introduced by Electric Pump through holes drilled into the wall at the recommended intervals and heights.
  • Silicone Gel or Cream injected into the mortar joints. This approach is especially useful on party Walls between separate dwellings when disruption is to be minimised and in order to conform to the Party Wall Act of 1997.
  • Injection Mortar to form a continuous barrier against salts trapped within the masonry of the wall and which will block capillaries.
  • An Electro Osmotic Damp Proofing System is also available which takes the form of an electric current introduced into the wall. The current will reverse the polarity of the charge within the wall and act to stop 'creep' of water molecules up a porous structure.

Any System has its uses and suitableness and our qualified surveyor can advise you further at the time of an inspection.

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Call us Freephone 0800 030 2121


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