How do traditional treatments work?

Prior to the availability of the Lectros Electro Osmotic System in Australia the two common methods of creating a new dampcourse were, chemically, or by the insertion of a new waterproof membrane. Let’s take a look at these methods to fully appreciate the outstanding Lectros system.

Chemical treatments

The Building Code of Australia prohibits the use of chemical damp-courses in new construction. These treatments attempt to create a damp-course by impregnating the masonry’s pores/capillaries with hydrophobic (non-wettable) chemicals. The chemicals impregnate the masonry and line the pore/capillary walls to make them non-wettable to nullify the spread characteristics and lifting effects of moisture. They do not block masonry pores or capillaries. Pressure injection systems require a series of 10 to 12mm diameter holes drilled along the walls about 150mm apart (about 2 holes per standard brick).

Generally, up to a 100mm radius of masonry is impregnated via each injection point. The chemical is forced under pressure into the masonry material and although most manufacturers provide indicative usage rates most contractors rely on visible surface staining as an indicator. This physical impregnation can also be achieved in dry walls. Gravity-fed, (diffusion), systems use chemical reservoirs that drain into pre-drilled holes in the masonry. It’s a slow process that may take up to 44 hours depending on the chemicals, masonry thickness and permeability. Leading manufacturers of gravity fed damp-course fluids limit their achievable penetration depth to 100mm below the installation points. This “soaking” method is also suitable for use in dry walls.

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Ready to use thixotropic materials such as Ultracure™ DPC Cream are injected into the damp masonry mortar course with a hand pump for the treatment of rising damp in masonry walls. The silane/siloxane based emulsion is specially formulated for injection into damp masonry The “volume specific” installation procedure ensures that the correct quantity of material is installed to treat a specific volume of masonry. Relying on the moisture content of the masonry to assist diffusion, Ultracure™ Cream will not dissipate or migrate very well in dry masonry. Some “ready to use thixotropic material” manufacturers advise that their products may not be suitable for use in wet walls or walls suffering from serious rising damp damage. – e.g.

If any of these methods fail to impregnate the entire thickness of the wall, any untreated sections will provide a moisture "bridge". Manufacturers of these chemicals specify the correct installation height in relation to the structural floor timbers. So, if you consider chemical treatment, ask where chemicals are to be installed and will the treatment arrest the damp under the timber floor bearers?

Undersetting (Physical Membrane Replacement)

This is normally achieved by removing a mortar bed-joint throughout the full thickness of the masonry wall with a modified "chain-saw", a section at a time and inserting a flexible membrane or "pillow". The bed-joint is then packed with fresh mortar or, the "pillow" is pumped full of mortar or grout expanding to fill the bed-joint. The process may be extremely disruptive and expensive with the possibility of bricks dropping. Physical damp-course membranes must be visible and not "bridged" by mortar, render or plaster.

Even if the chemical system or membrane replacement has been successful, the salt contamination already present will attract atmospheric moisture and give the impression of rising damp. These methods of rising damp repair should incorporate the removal of salt contaminated plaster, followed by re-plastering with a salt-retarder additive in the plaster mix. (This may hide damp-course failure, even from an electrical moisture meter, until the height of internal rising damp exceeds the height of the new plaster!)

What to be wary of… Assessments by the C.S.I.R.O. or the B.B.A., Architects, Engineers, Building Surveyors or Builders will all confirm that every masonry dampcourse must be effective below any supported suspended timber floor components.

Pressure Injection of a brick wall

Chemical and membrane replacement treatments attempt to cap the height of the rising damp. The correct procedure for both methods requires installation below structural floor timbers around the outside of the house at about 150mm above ground level or inside under the level of the existing floor bearers. With both treatments, the walls below the treated sections will still be effected by rising damp and still remain subject to mortar decay and brick fretting and when installation occurs above timber floor level, the bearers will be supported by damp masonry.

Mortar loss and brick decay can often be seen on unprotected masonry between the soil level and the damp-course. This is not uncommon where masonry structures are built on sloping sites having a damp-course located many courses above soil level.

Common practice when treating brick cavity walls is to treat only the internal brickwork. So mortar droppings in the cavity may create a bridge to a still-damp outer leaf. Should only one leaf of a masonry wall be treated, removal of debris from the cavity is vital unless the contractor can confirm that the debris has also been treated.

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