All Category

Waterproofing for Internal Wet Areas – Defects and Rectification


Leakage through walls and slabs can lead to either architectural or structural defects, depending on the extent of leak. Some of the common defects arising from such leaks are as given in Fig 8.2. Detailed investigation will help in ascertaining the cause or causes of the problem. The repairs of such problems vary based on the causes determined. In general, the substrate is thoroughly cleaned and repaired/ restored prior to reapplying with suitable waterproofing materials. As leakage repairs are often expensive and disruptive, the principle of “do it right the first time” is certainly relevant for waterproofing.


The application of a waterproofing system requires extreme care, supervision, and strict adherence to the manufacturer’s recommended procedures. Poor workmanship would result in leaks that are difficult and costly to repair. Apart from workmanship, wear and tear over time and improper renovation works may also lead to leakage. The main causes of leakage include natural deterioration of materials, poor workmanship at time of construction and improper subsequent renovation works.

Ceiling leakage is likely to occur over time due to deterioration of the integrity of the waterproofing membrane or floor screed, degradation of pointing between tiles and wall/ floor joints and also deterioration of concrete infill/ grout around pipes. Faulty pipes/ sanitary fittings/ fixtures such as leakage at joints of concealed pipes and misalignment at sanitary discharge pipes may also lead to leakage.

Materials for Repair

The pre-packed waterproofing screed, as explained in Chapter 2, is able to produce good bond strength with low shrinkage. The use of pre-packed waterproofing screed allows better site control of quality and housekeeping.

Flexible cementitious membrane (or other approved water-based membrane) is recommended because it requires much less stringent surface preparation compared to solvent-based polyurethane membrane. It is able to achieve adequate bonding to the substrate even if the surface is wet and not totally free of dust.

Chemical grouts are materials which mix readily with water at the time of application. As such, chemical grouts provide good penetration of wet joints and cracks. Chemical grouts react with the water to form a waterproofed solid, stopping the water that is infiltrating the structure. A common chemical grout used to seal off leaks in concrete is the polyurethane injection grout, which upon contact with water, expands and forms a tough, flexible foam seal that cannot be penetrated by water.

Rescreeding Method for Rectification of Ceiling Leakage

In general, this provides a more effective rectification to ceiling leakage. All the floor tiles, screed, squat or pedestal pan and any other fixtures are first removed. Areas around pipes should be hacked slightly deeper (about 25mm more). Hacked surfaces should be cleaned free of loose particles. Ensure proper preparation of floor surface (eg, existing floor tiles/ screed to be completely removed, hacking around pipes/ gully trap). The hacked areas around pipes are then filled with a suitable material such as non-shrink grout. Ensure that the application of non-shrink grout is according to manufacturer’s instructions.

A good quality waterproofing membrane is applied and left to cure to the manufacturer’s requirements. A new layer of waterproofing screed is subsequently laid on the membrane after the membrane is sufficiently cured. Please refer to Chapter 5 — 7 for more details on the preparation of the surfaces, membrane application and laying of screed.

New floor tiles are subsequently laid and the pedestal pan (if applicable) and any other fixtures are re-installed. If squat pan is to be re-installed, this should be done after the membrane had cured and before screeding work is carried out.

Injection of Chemical Grout

This method of rectification results in lesser inconvenience to the homeowners as the repair work does not require hacking of floor tiles and removing of existing fixtures.

In cases where leakage is observed, the specialist should first locate the crack which is causing the leak. Before
any rectification work can proceed, the crack and surrounding concrete should be thoroughly cleaned (by mechanical means) to remove all loose, unsound, friable and deleterious materials. A 45-60 degree angle hole should then be drilled so as to intersect the center of the crack at a depth of approximately 1/3 thickness of the concrete. The center to center distance between the drill holes will depend on the characteristic of the proprietary product used and site conditions. To remove debris and improve penetration, the crack should be flushed with water prior to resin injection. A plastic injection packer is then inserted into the hole.

If the proprietary product is made up of 2 components, care should be taken to ensure correct mix ratio of the components. It is a good practice to test out a small amount as sample first. The chemical grout is then injected through the nozzle into the crack line using a suitable pump, at the specified pressure. Injection is considered complete once excess amount of unreacted grout is observed to appear from the crack.

Upon completion, the plastic packers can be removed. The face of the joint and the excess materials should be cleaned on the following day and all holes are to be filled using an approved material eg, non-shrink grout.

Source from BCA Singapore