Practical knowledge for better construction.

There is no single waterproofing system that is best for every concrete roof.

The appropriate system depends on the condition of the roof, the existing screed or coatings, cracks and movement, drainage, penetrations and junctions, whether the waterproofing will remain exposed to sunlight and weather, and whether other finishes will be installed above it.

For an exposed roof, the selected system should be suitable for the expected external exposure and substrate conditions. Particular attention should also be given to roof outlets, penetrations, cracks, construction details and roof-to-wall junctions.

The roof should therefore be assessed before selecting the waterproofing system rather than choosing a product based only on price or availability.

Sometimes, but the existing roof should be assessed first.

Applying a new waterproofing system directly over a failed roof without understanding why it is leaking can result in another failure.

The assessment should consider the condition of the existing waterproofing, adhesion to the substrate, cracks, damaged areas, trapped moisture, drainage, outlets, penetrations and roof-to-wall junctions.

The compatibility of the proposed waterproofing system with the existing surface must also be considered.

Depending on the condition of the roof, the existing waterproofing may be suitable for preparation and local repair before receiving a compatible new system. In other cases, deteriorated or unsuitable materials may need to be removed.

The correct approach should therefore be based on the actual roof condition and the cause of leakage rather than simply applying another waterproofing layer over the existing surface.

Waterproofing failure is not always caused by the waterproofing material itself.

Common causes include selecting an unsuitable system for the application, inadequate surface preparation, untreated cracks or movement, poor detailing around joints, penetrations and drainage outlets, incorrect material consumption or application thickness, and working outside the conditions specified for the system.

Problems can also occur when the source of water has been incorrectly diagnosed or when a completed waterproofing layer is damaged by subsequent construction activities.

Successful waterproofing therefore depends on the complete system: correct diagnosis, appropriate product selection, a sound and properly prepared substrate, careful detailing and correct application.

When an existing waterproofing system has failed, the cause should be investigated before another layer or repair system is applied.

Repainting alone will not normally solve a wall moisture problem if the source of the moisture is still present.

Recurring dampness, fungus, salt deposits, bubbling or peeling paint can have different causes. These may include rainwater penetrating through external walls, leaking roofs or plumbing, moisture entering through cracks and construction details, condensation, poor ventilation, or ground moisture affecting lower sections of walls.

Because these problems can look similar at the surface, identifying the likely source of moisture is an important first step.

Where necessary, damaged or unsound plaster and finishes should be removed so the underlying wall can be assessed and appropriately treated. The required remedial system will depend on the source of moisture and the condition of the substrate.

Only after the moisture problem has been addressed should plaster, skim coat and decorative finishes be properly reinstated.