Rising Damp

Rising Damp in existing buildings usually occurs as a result of one or more of the following reasons:
  • No Damp Proof Course (dpc)
  • Failed dpc
  • Bridged dpc
No dpc  - All modern buildings should be fitted with black plastic dpc sheeting that is fitted under the floor slab and which exits the side walls 2 brick courses above finished exterior ground level. However, many buildings built before the 1960’s, when dpc sheeting was first made available, were built without any form of dpc. Some were built with suspended wooden floors with a void beneath to ground level. Moisture rose in the clay stock bricks and evaporated out through the bricks beneath floor level, being circulated by way of air bricks. Over time many air bricks were either sealed off or the voids filled with concrete, causing damp to rise in the brickwork and drawing with it damaging slats from the ground. When this happens damp can be stopped by one or more of the following products:
  • Dryzone Cream
  • Dry Rods
  • Microsilan
  • ECS Epoxy Floor Coating
  • DryBase Liquid Applied DPM
Failed dpc – One of the precursors of the black plastic dpc sheeting was a product called malthoid. This bitumen-based product becomes brittle over time, developing cracks in its structure which allows moisture to pass through. Regrettable this deterioration takes place indiscriminantly giving rise to damp in some areas and not in others. A similar problem can occur with older methods of creating a chemical dpc where high pressure injection pumps were used. Where too high a pressure was used, some of the brickwork may not have been completely saturated, leaving some areas unprotected. Over time moisture discovers the weakness and rises through the unprotected pores to affect upper surfaces. Once again these conditions can be treated with the same 5 products above.
Bridged dpc – The practice of plastering external brickwork to buildings down to ground level without exposing the dpc sheeting has resulted in many new buildings suffering from rising damp within a matter of months of being occupied. Plaster, usually 25mm thick or more, is applied to the walls completely covering the dpc. This allows moisture to rise in the pores of the plaster above the height of the dpc, causing damage not only to external plaster above the height of any dpc that may have been fitted but also to internal surfaces as the moisture is drawn inwards. Provided that the dpc sheeting is intact, and this can only be verified once external damaged plaster is removed, it should not be necessary to create a new chemical dpc. Damaged plaster on both sides of the wall will need to be removed and replaced, ideally with a salt retardant in the new plaster mix, and the external brickwork protected with a waterproof slurry prior to the application of new plaster. Products for this treatment would include:
  • Latseal Slurry
  • Bondaid Plus
  • Renderguard Gold

Introduction to Rising Damp

How Does Rising Damp Occur

Treating Rising Damp With Dryzone Cream

Installation of Dryzone Cream

An example of rising damp

An example of rising damp

Treatment of Rising Damp using Dryzone damp-proofing cream.

Treatment of Rising Damp using Dryzone damp-proofing cream.

For more information please contact us on 011 708 3603  or 021 982 5131.

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