Slab edge dampness occurs when the exposed edges of concrete slabs are rocked with persistent dampness. It is caused by a variety of factors ranging from poor quality construction to poor drainage and prolonged damp weather conditions.

It happens when moisture is sucked into the concrete via capillary action or through the air sacs in the concrete material. Usually, with slight exposure to moisture, only the surfaces of the concrete slabs will be exposed to dampness. However, with repeated and more extensive exposure, the slab edge dampness and even some moisture ingress begins to occur on your concrete structures often with devastating consequences.

Slab edge dampness does not affect well-constructed houses with concrete slabs or footings that are fairly well detailed. Problems generally occur when susceptible surfaces come into contact with prolonged wetting such as during the long rains, contact with the ground or from garden watering. While dampness is normally limited to the outside surfaces, there are instances where the water or moisture permeates the concrete structures and reaches the interior part of the house causing damages to the floor finishing and walls. At the very least, it could leave some ugly watermarks on your surfaces but there are instances where prolonged exposure may lead to a pungent smell when it comes into contact with other objects in the house such as carpets.

The best control is preventative. You can begin by ensuring that your premises are well protected from the dampness during the construction phase. This is a far more effective approach than having to repair or renovate to remedy problems causes by slab edge dampness. Before corrective measures are instituted, it is also prudent to carry out a thorough investigation of the dampness problem to determine the best course of action that will eliminate the issue at its source.


Causes of Slab Edge Dampness

The slab edge dampness occurs as a result of moisture seeping into concrete materials via capillary action. When the slabs or footing are exposed to damp conditions long enough, the moisture is sucked into the material via the tiny pores or air sacs in the concrete. This occurs due to prolonged exposure to dampness. Intermittent exposure results in largely “harmless” surface dampness.

Due to the fact that the building works normally occur during the long dry seasons, the slab edge dampness or moisture ingress will not be apparent until it is too late when the house is already finished or occupied. The problem can also get worse post-construction, during landscaping works or when the building is undergoing some alterations. If not done with quality workmanship and expertise, certain alterations may exacerbate the pre-existing drainage problems in the building leading to slab edge dampness. Other causes include the following:

  • Lack of proper detailing or proper installation of the moisture barriers on the slab edge and external walls of the building.
  • Poor drainage or poor stormwater discharge leading to prolonged exposure of the slab edges to moist conditions.
  • Poor construction practices with regards to the slabs or footings.
  • Direct contact between the concrete structures and the ground.


Signs of Slab Edge Dampness

The slab edge dampness will manifest itself in multiple ways. Common signs include the following:-

  • Persistent dampness in the affected parts
  • Mould growth
  • Rusting or surface corrosion that are adjacent to the exposed surfaces.
  • Watermark stains
  • Musty smell or bad odour on your floor coverings
  • Peeling off of external paint in the exposed part
  • Delaminating render


Managing Slab Edge Dampness

The best measures are preventative so start by choosing a qualified builder who understands the problem and takes it seriously enough. Good drainage and good construction practice are also key to managing the slab edge dampness and moisture ingress issues.