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Rising Damp FAQ

What is the rising damp by definition?

Rising damp (dampness) is ground moisture containing salts rising up a masonry wall.

What causes rising damp?

Rising damp occurs as a result of capillary suction of moisture from the ground into porous masonry building materials such as stone, brick, earth and mortar. The moisture evaporates from either face of the wall (inside or outside), allowing more to be drawn from below. The height to which the moisture will rise is determined by the evaporation rate and the nature of the wall. The normal limit for rising damp ranges from 0.5 to 1.5 metres above ground level.

The only way in which rising damp can be stopped by the introduction of an impermeable horizontal barrier at the base of the wall. This barrier is commonly called a damp-course.

What are the signs of rising damp?

Rising damp may show as a high-tide-like stain on wallpaper and other interior finishes, and, when more severe, as blistering of paint and loss of plaster. Damp walls encourage the growth of moulds, which, with the high humidity, can lead to health problems for occupants. Externally, a damp zone may be evident at the base of walls, with associated fretting and crumbling of the masonry.

Some or all of the below symptoms may be present.

Internal walls: peeling or bubbling paint, peeling or bubbling plaster-work, water tidemark, efflorescence, paint deterioration, rotting timber skirting boards

External walls: efflorescence, water tidemark, fretting brickwork, crumbling mortar

Key tell tale signs of rising damp are,

  • Tidal mark and or damp patches or stains at low level (less than 1.2-1.5m)
  • White, floury salts (efflorescence) in the form of nitrates, chlorides and sulphates on the wall (these are rarely found from other water sources)
  • Fungal decay in skirting boards
  • High progressive moisture readings at low level

What is salt attack?

Salt attack is closely associated with rising damp it is the decay of masonry materials such as stone, brick and mortar by soluble salts forming crystals within the pores of the masonry. As the crystals grow the masonry is disrupted and decays by fretting and loss of surface skins. The salt commonly comes from the soils beneath and is carried up into the walls via the rising damp whereby the salts are left behind, slowly accumulating to the point where there are sufficient to cause damage. Repeated wetting and drying with seasonal changes leads to the cyclic precipitation of salts and the progressive decay of the masonry.

How do damp-courses fail?

Poorly installed DPCs that do not form a barrier across the entire wall thickness will be bridged by mortar in the joints or cavity. Concrete floors or external paths can form a bridge if the concrete, or the fill beneath , abuts the DPC with some form of verticle damp-proofing. Build up gardens and pavements against walls can also bridge the DPC. To be effective a DPC needs to remain about 150- 200mm above ground or paving level.

A typical list of why a DPC may fail:

  • breakdown due to chemical attack
  • cracking or penetration during installation
  • breakage by differential settling of the building
  • incorrect installation
  • bridging by pointing or rendering
  • bridging by the installation of garden beds and paving
  • bridging by mortar droppings collecting in the wall cavity
  • bridging by renovations or additions, eg incorrect replacement of a timber floor with sand and a concrete slab.

Does rising damp cause health risks?

Health risks can range from respiratory infections to aggravating asthma can also be associated with houses with damp subfloors, rising damp and other damp problems.

Where does rising damp occur?

Rising damp occurs in heritage brick and stone houses which lack an adequate damp-course. Most commonly found in Victorian and Edwardian structures and Californian bungalows, however more modern bricks can also suffer & can also be treated.

Why does a damp-course break down?

The two most common causes are deterioration of the damp course due to age and burying of the existing damp-course with internal concrete floors or external paths and earth levels.

Does rising damp affect the value of my house?

Yes, because when it comes time to sell, the prospective buyer will order a building inspection which will reveal the problem (with the use of a moisture meter) even if it has been covered up. This discovery results in the loss of the sale or at least a heavily discounted price.

How can I stop rising damp?

By damp proofing the wall by installing a new damp-course at the base of the masonry wall. This can be achieved either by using the Tech-Dry DIY Damp Course Installation Systems or by employing a specialist contractor.

How durable are the Tech-Dry Damp Course Systems?

The Tech-Dry Damp Course is a tough durable polysiloxane barrier that is both alkali and UV stable.

How easy is it to install the Tech-Dry DIY Damp Course System?

It is quite simple and easy. A hammer drill with masonary bit is all that you need once you have your Tech-Dry Kit. For detailed instructions please view How to fix rising damp or contact us.

What do I do after installing the Tech-Dry Damp Course System?

After damp proofing your wall by installing your new damp-course , it is imperative that all treated walls be replastered/re-rendered after an adequate drying out period. For detailed information, please download the post wall treatment link to the right or contact us. 

I have mould on my walls, how do I fix this problem?

Mould is a ventilation issue and therefore is not caused by rising damp. Improving ventilation can be achieved by increasing the number of sub-floor vents and the opening of doors and windows, preventing steam from bathrooms and kitchens from escaping into living areas. For more detailed information on the issue and instructions for remedial action please look at the CSIRO reports on improving sub-floor ventilation, mould growth in houses, and condensation in houses.

For more detailed information on the issue and instructions for remedial action please look at the CSIRO reports on improving sub-floor ventilation, mould growth in houses, and condensation in houses.

Renovators & rising damp

One of the worst mistakes made by renovators is to remove a ventilated timber floor and replace it with a concrete slab poured on sand or other fill.

The concrete and its associated damp-proof membrane prevent evaporation, and the soil moisture rising beneath the building becomes focused on the walls. Rising damp problems are almost guaranteed.

Drainage problems

Many times, issues arising from rising damp can be a combination of both rising damp and drainage problems. Bad drainage can magnify the problem considerably. Many times a new silicon damp coarse is required as well as rectifying the drainage problem. 

  • If you have a question pleas call 1800 832 437 and our technicians are happy to help.