Rising damp

What is 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.

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.

The Preferred System

Over the past twenty years a wide range of damp proofing systems have been used to prevent rising damp. These include both practical and obscure methods; some which have been short lived, due to difficulty in installation, dubious effectiveness and in some cases detrimental effects to the treated building.

Pressure injection chemical damp proof courses have been successfully used since 1960 and. is a nominated method on restoration projects throughout the world.

Dyco-damp proofing introduced the injection system to Australia in 1976.

The Westox Injection System has consistently been used by Restoration Bodies on many of Australia’s oldest buildings, ranging from Victorian Terraces to major conservation projects.

The advantage of this injection system includes the level of installation which may be lower than some other commonly used methods This provides protection to the skirting boards and can avoid dampness bridging through the new plaster. Speed and cleanliness of installation are two other factors in arriving at an objective choice.

Approved Applicators of the Westox Chemical Damp proof Courses carry out a careful survey of the problem and provide a written report and quotation.

As an accurate diagnosis is critical in making an appraisal of any dampness problem, an electronic meter is used to assess moisture content and to identify it’s source. It is not uncommon to see properties treated at great expense for rising damp when the problem could be as simple as a broken down pipe or other minor repair.

After the installation of the new damp course, the walls will gradually dry out. Depending on the moisture content and the thickness of the walls, this could take excess of one year. The replacement of all damp affected plaster is essential to prevent secondary dampness.

Salt contamination of the old plaster is caused by the moisture containing salts, rising up through the capillaries of the brickwork from the ground below.

These salts build up in the plaster over a period of the time and attract airborne moisture. It is the expansion and contraction of these salts which cause the familiar rising damp symptoms of eroding and blistering paints and plaster. The major proportions of the salts are removed with the old plaster. The new render is designed to allow the passage of water vapour, so that residual moisture can dissipate from the wall With the use of a special cement additive called Westox salt retarder, the old plaster can be replaced soon after the installation of the new damp-proof course.

On the commencement of a typical rising damp project the applicator removes the original skirting, which may be refitted after the installation of the chemical damp-proof course and the completion of re plastering. In some cases the skirting may be rotten and require replacement.

 

The damp affected plaster is then removed to expose the brick or stone After selecting the course of brick or stone which will become the new damp-proof course, a series of 10mm holes are drilled at an appropriate depth and space.

The injection lances are then introduced into the holes and a seal is formed by a rubber expansion washer which holds the lance firmly into the brick or stone.

The selected Westox Injection Fluid is then pumped via flexible tubing into the brickwork and the fluid, now under pressure is forced through the capillaries of the brick or stone until it is visually evident that saturation has taken place.

The lances are then removed and the procedure is repeated progressing along the wall to be treated.

The injection fluid continues to penetrate through masonry and mortar joints by capillary action for approximately 24 hours. After the full thickness of the wall is injected the continuous saturated section of masonry will become the new damp-proof course. After a short drying period (7-10 days) the render-plaster may be replaced to complete the job

The Westox Chemical Damp-proof Course is covered by a written 20 year warrantee but only applies if the work is undertaken by a Westox Approved Contractor.

Technical Specifications
Standard specification
(Pressure Injection)

Remove Skirtings where applicable. Remove damp effected plaster to a height of 400mm above the highest point at which dampness can be detected (a suitable moisture meter should be used.)

Drill 10mm holes in the brick or stone to predetermined depths and spacing.

Introduce injection lances into holes and activate expansion washers. Proceed with injection through multi lance harness until it is visually evident that full saturation has been achieved.

Usage
The rate of fluid used will be relative to the porosity of the materials and the thickness of the walls. As a general guide the fluid requirements are in the region of 1.5 to 2 litres per 110mm thickness of wall per lineal meter.

Replastering
After the “drying out” period (minimum of seven days) the walls are to be replastered to the following specification.

Mixing Water
40 Parts fresh water to 1 part Westox Salt Retarder (e.g. 500mls per 20 litres water)

Cement Mix
1 part OP Cement, 3 parts washed sharp plastering sand.

Note: Important do not add lime, plasticiser or any other additives. General purpose cement must only be used (not builders cement)

Mix to a workable consistency and apply at a minimum thickness of 10mm.

After overnight drying the wall may be set finished with a mixture of hard wall plaster and hydrated lime.

Should a sponge finish of render be required, a second coat of render must be applied on the same day as the salt retarding coat. This finish coat is to be of 6 sand, 1 cement, 1 lime.

After adequate drying either the original or replacement skirtings may be fitted.

Precautions and First Aid
A Westox 50 Material Safety Data Sheet should be provided to all persons handling the product.

Storage
Store in a cool dry place.