Roof waterproofing: A critical challenge for high-rise buildings

Sanjay Bahadur explains that high-rise buildings have suffered continuous assaults with consequential interior damage due to the intrusion of wind and water therefore waterproofing of roofs is a critical challenge and the methodology varies from case to case basis.

Sanjay Bahadur

Sanjay Bahadur

High-rise building or Skyscrapers have always been an attraction especially for a city like Mumbai buzzing with life and ever increasing population with very little place to accommodate them and expand further. Through the last five to six decades, the building industry has been revolutionised in Mumbai, keeping in pace with the rapid industrialisation, urbanisation, and population. But at the same time, these high-rise buildings have also suffered continuous assaults with consequential interior damage due to the intrusion of wind and water. Greater the height, greater are the chances of being exposed to various climatic danger and vulnerability.

Water which is elixir of life, poses to be a serious enemy to hydrophilic concrete structures. Water leakage or more categorically moisture ingress in buildings results into damp, uncomfortable internal environments; deterioration of internal decors (including mould growth); unsightly damp areas on wall and ceiling surfaces. The dissolved gases and harmful pollutants in water affect the underneath steel bars resulting into corrosion distress.

The other predominant factors for the higher degree of deterioration in Mumbai are the predominant uses of Ordinary Portland Cement (OPC) as the major construction material prior to nineties and the poor maintenance management practices by the housing societies in Mumbai. OPC, though a versatile construction material is prone to formation of cracks due to the heat liberated during its setting process.

The problem thickens up at exterior faces of the structure especially roofs of High rises, due to the heavy downpour during the monsoon. Surface Cracks open up the passage of water; percolating inside the building causing serious damage to the structural elements and increased concentrations of harmful pollutants affects occupant’s health.

Waterproofing of Roofs – A Step by Step Approach


Waterproofing of existing roofs is a critical challenge and the methodology varies from case to case basis. It is first important that you understand why the leakages happen from the roofs:


  • Improper slope of the roof surface leads to water stagnation
  • Defective enclosure for over head water tanks may lead to continuous accumulation of water on the roof surface
  • Cracks on base slabs and parapet walls make the pathways for the water to move inside the building elements.
  • Vegetation growth on the terraces allows the moisture to percolate through their roots embedded inside the slabs.
  • Inadequate protection of roof slab or improper installation of waterproofing system may also lead to leakages.


As the reasons are varied, a proper systematic approach can lead to an effective result


  1. Visual Observation
  • Slope of the roof surface and position of service pipelines are adequate to drain out the water
  • Visibility of cracks on the surface absorbing the water inside
  1. Expert Diagnosis
  • Condition of the roof slab
  • Depth of cracks on the surface
  • Moisture content
  1. Structural audit

It is recommended only in case of heavy and all over leakages through various building sections

  1. Specifications and recommendations

A proper waterproofing methodology is to be sketched after all the data are analyzed and then accordingly the right products / systems have to be specified.

4.1. Conventional vs. Advanced Waterproofing Techniques

Though the roof waterproofing done by conventional waterproofing systems like Bitumen, Brickbat coba, mud phuska proved to be successful against times, but they have their inherent problems like short life and long installation procedures delaying the time-bound projects. Climatic changes and weathering effects are one of the major issues for the non acceptability of these techniques. And, when we talk about specifically about very popular brickbat coba (BBC) as roof waterproofing, the system technically fails to provide any waterproofing solution. The porous bricks and in-filling mortars used absorb a lot amount of water inside the system and ultimately turns out to be a water pool rather that a watertight barrier. Another major issue with BBC is its dead weight on the slab structure.

The advancements in waterproofing materials and technologies have revolutionized the modern construction industry, not only with their ease of applications but also longer durability and less maintenance aspects.


These include:

A) Liquid applied coating / membrane systems

  • Polymer modified cementitious coatings
  • Hot and cold applied bitumen coatings
  • Acrylic copolymer based liquid applied membrane systems
  • Polyurethane based liquid membranes

B) Preformed sheet membranes / barrier systems

  • Polymer (APP / SBS) modified bitumen sheet membranes
  • EPDM rubber membrane
  • TPO Membrane

4.2. Selection of Materials and Techniques

The selection of the right material depends on the type of roofs, climatic conditions and suitability of application. Normally, coatings or liquid applied membranes are used for small terraces while sheet membranes are the best options for large terraces. Moreover, one must also ensure to check the thermal coefficient and elastomeric property of the systems before application on the base slab. A mismatch in thermal coefficient would lead to the failure of the system while undergoing thermal expansion-contraction cycle.

The expansion or isolation joints in the base slab, in case of large terraces should be protected with elastomeric polysulphide based joint sealants.

Penetration of water normally takes place through hairline cracks, joints, honeycombs, holes and punctures. Specialised polymeric crack filling material or polymer mortars should be used to fill up those areas and the external faces to be covered with weather resistant protective coatings rather than decorative finish paints.

Removal of unwanted vegetation along the building facades and subsequent filling of gaps with moisture insensitive polymeric mortars would be the right choice.

  1. Application of waterproofing materials and systems

Application of waterproofing materials is unique as per materials and manufacturers’ specifications. When considering the millions of square feet of waterproofing systems installed and miles of sealant involved in building envelopes, it can be estimated that only 1 percent of envelope failure and resulting leakage is actually attributable to materials or systems actually failing. The reasons typically involved in failures include human installation errors, the wrong system being specified for in-place service requirements (e.g., thermal movement encountered exceeds the material’s capability), the wrong or no primer being used, inadequate preparatory work, incompatible materials being transitioned together, and insufficient – or in certain cases such as sealants, too much – material being applied.

Fundamentally, waterproofing failures are attributable mostly for improper preparation of base surface before installing the system – hence it requires an utmost important to keep a proper watch while installation of a system is to be undergone. For example, cleaning of loose particles, oil etc. followed by checking of moisture content before application of a sheet membrane or preparing a surface saturated dry (SSD) substrate before application of a polymer modified cementitious coating are the prime requirements to get the desired results.

  1. Protection and Maintenance Requirements

As any material requires maintenance, whether be it a human body or a car of your choice, roofing treatments should also be kept under a proper maintenance schedule. For example, any unspecified movement without adequate protection over a coating will lead to the rupture of the film; the bitumen sheet membrane should be protected from direct sunlight by providing either a protecting screed or a protective aluminium coating over it.

Over and above, maintenance plays a vital role to save your own property deteriorated from nuisance factors. Cleaning of terraces, regular checking of vulnerable areas like rain water outlets, plumbing lines etc. help the structures to last for a longer life.

The awareness of waterproofing & its implications is a must consideration for today’s engineers engaged in building of durable structures. Otherwise, we will continue to spend money only on repair and maintenance rather than creating the best infrastructures.

(The author is Global CEO, Construction Chemicals, Pidilite Industries Ltd.)



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