Defective or Bridged Damp Proof Course

Dampness can cause lifting of tiles and also the defilement of walls, floors and furnishings, if preventive measures are not taken in the building stage. Damp proofing is to be done as per the Building Code of Australia and Australian Standard AS3700 Masonry Code. Walls must be constructed in such a way as to limit the spread of moisture.

A Damp Proof Course (d.p.c.) is a lining of material in the walls close to the ground functioning as an impermeable barrier against moisture to the building. As their role is to prevent the upward permeation of dampness, they must be continuous and extensive enough to cover the entire width of walls. At times these damp barriers fail to function due to the effects of fungal decay or poor masonry. There are certain common symptoms to indicate the spread of moisture.

Symptoms of Dampness

• Walls will show localized or discolored patches or “tide marks”
• Surface patches of water-soluble salts may become visible on the walls
• Skirting boards may be affected by fungal decay
• Wood flooring may also be weakened
• Extensive fragmenting or fretting of masonry may become prominent where the osmotic pressure of “crypto-efflorescence” causes moisture to rise up the wall.

Serious structural problems may arise when the d.p.c. cracks due to structural movement. Efflorescence, timber decay or fretting is the outcome of such cracks. The waterproofing compound used in the d.p.c. might not be adequate to stop the movement of moisture. This is detrimental for the health of walls, flooring, furniture and appliances coming in contact with damp areas.

How to Know that d.p.c Needs Replacement?

You will need to check for a few things to understand when or in which places d.p.c. needs to be renewed.

• When the d.p.c. is fractured due to foundation movement
• When the d.p.c membrane is bridged; it is not placed through the full width of the wall
• Where mortar droppings in the base of the wall cavity pile up and cover the stepped flashing/d.p.c , thus allowing dampness to encroach from the outer to the inner side of the walls.
• Places where concrete paths and verandahs laid without membranes are above the damp proof course
• Areas where street levels have been raised and gardens cover sub-floor; hydrostatic pressure from a leaking drain or a raised street level adversely affects the d.p.c.

The d.p.c. treatment will involve replacement of the layer and also the repair of plaster, because it is the wetness of the plaster that aggravates the spread of moisture upward and sideways. Usually a plastic bag is inserted into the joint and then pumped full of a quick-setting mortar to ensure support. Placed in the horizontal gap, this layer acts as the new damp-blocking membrane.

As a layman, it will be next to impossible for you to check for so many instances of structural deformities. It is always wise to trust building inspection experts in order to draw exact conclusions.

The Inspex team can help you with the detection of any form of structural issues of a building. Our inspectors are willing to travel across southeast Queensland to guide home owners or builders on every aspect of property inspection in building stage or pre-purchase stage. Our illustrated reports are based only on facts gathered by the usage of scientific methods such as Thermal Mapping. We also suggest ways of renovation so as to help reduce chances of structural damage to a great extent.