How to stop water leakage from concrete roof? – Causes of Leakage

Concrete prepared under a nominal mix can retain water up to a certain extent depending on the corresponding pressure applied. This capacity of the nominal concrete mix to retain water increases with the grade of the concrete.

It also depends on the age and surface condition of the concrete structures. However, without the implication of waterproofing admixtures or other mix design methods, concrete itself is not 100% waterproof.

How to stop water leakage from concrete roof? - Causes of Leakage

Before discussing how to stop water leakage from concrete roof, let us know something about its causes and symptoms.

Causes of water leakage from concrete roof

Cracks, pores, and joints in the concrete structure acts as a passage of least resistance for seepage of water through them resulting in water leakage. The major causes of formation of this seepage path in concrete structures are listed out as follows:

  1. Cracks in slabs may arise due to excessive deflections caused by overloading, implementation of faulty structural design, inadequate design considerations.
  2. Adoption of higher water-cement exceeding 0.6 to 0.7 makes the concrete more porous and permeable resulting in capillary action.
  3. Extreme climatic conditions result in simultaneous thermal expansion-contraction, shrinkage, creep resulting in the formation of cracks with can be prevented by providing joints.
  4. Ineffectively filled expansion joints and other construction joints (Cold joints) may result in water leakage in concrete structures.
  5. Improper aggregate proportion, poor mixing, and inadequate compaction will result in honeycombing of concrete forming larger voids.
  6. Poorly/uniformly graded aggregate materials also result in a large number of pores and weaker bonds in concrete structures.
  7. Spalling of concrete due to corrosion of reinforcement give rise to cracks.
  8. Vegetative growth in concrete structure give rise to cracks and abrasion.
  9. Adaptation of improper construction techniques, poor construction quality, and poor workmanship may result in faulty concrete structures full of formation of cracks and voids.
  10. These includes the defective gradient of roof slab resulting in trapped rainwater.
  11. Use of waterproofing materials likes tiles and marbles of poor quality.
  12. Poor quality surface finish works of the terrace (screeding works).
  13. Defective design of overhead water storage tanks.
  14. Poor plumbing works resulting in leaking pipes and pipe joints which are embedded inside the slab.
  15. Depending only on chemical Waterproofing and excluding roof surface works.

Symptoms of water leakage from concrete roof slab

Visibility of damp spots, visible cracks, vegetative growth, and reduced water pressure in taps can signify the water leakage in concrete slabs

How to stop water leakage from concrete roof?

Waterproofing of the concrete structures can be done either on the interior/exterior side or within the concrete itself. Various methods which can be adopted to prevent or stop the water leakage which is listed as follows

  • Sealing of Cracks and pores with the help of binging materials like cement, lime, waterproof membrane, etc.
  • Cracks in the concrete structures can be sealed using various concrete patching compounds like Epoxy resins, Acrylic resin. These compounds can be applied using a trowel or a putty knife and allowed to dry.
How to stop water leakage from concrete roof? - Causes of Leakage
  • Sealing concrete is the silicate-based sealant which is applied over the surface of the concrete with paint roller or brushes and are allow to be soaked up into the pores which then reacts with the lime in the concrete and expands, filling up the pores (Ex. Radon seal, High solid Acrylic sealers, etc).
  • Expansion joints and other construction joints in the concrete structure should be sealed with Non sag polyurethane sealant available in the market.
  • Various waterproofing admixtures (Example, Dr. Fixit,) can be added in the concrete before casting of roof slabs.
How to stop water leakage from concrete roof? - Causes of Leakage
  • Waterproofing admixture consists of mixture water repellant chemicals like oil, petroleum, powdered inert filler materials and hydrophilic crystalline material with reacts and generates pore filling deposits.
  • By applying waterproofing layers or membranes.
How to stop water leakage from concrete roof? - Causes of Leakage

Read also,Foundation waterproofing membrane – Different types and Materials

  • Plasters(screed) of C:S ratio  1:1 to 1:4 along with the waterproofing admixtures can be directly applied over the concrete layer or over another layer of coarser screed of cement sand and chip aggregate.
  • Bituminous or coal tar layer can also be applied to the concrete roof to make them waterproof.
  • Waterproofing tiles and marble slab can be laid over the concrete slabs with water seal joints to stop water leakage from a concrete roof.


Water leakage in concrete slab whether through crack or pores or joints results in the corrosion of the reinforcements. This affects the structural integrity of the concretes structure resulting in structural failure.

Thus for elongating the life span of the concrete structure, it should be protected from direct and prolonged exposure to water through the above-mentioned measures. 

I hope this article remains helpful for you.

Happy Learning – Civil Concept

Contributed by,

Civil Engineer – Jenish Shakya

Read Also,

Top 5 Cause of Honeycomb in Concrete – Remedies of Honeycomb

10 Cause of crack in concrete structure like Column, Beam, Slab, etc

Why curing of concrete is important | Different way of curing

Honeycombing in concrete | Types, Effects, and Remedies of Honeycomb

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"Structural Engineer" with over 5 years of experience in estimation, structural design, and surveying. I am passionate about using his skills to create safe and sustainable structures. I am also a keen writer, and I enjoy sharing my knowledge and experiences with others.

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