Concrete, renowned for its strength and durability, isn’t inherently waterproof. Exposure to water can lead to significant structural damage, including corrosion of reinforcing steel, freeze-thaw cycles causing cracking, and reduced overall lifespan. Therefore, effective waterproofing is crucial for the longevity and integrity of concrete structures. This article explores common methods employed to achieve this protection, categorized into extraneous (external) treatments and internal approaches.
I. Introduction: Concrete Waterproofing Methods
The preservation of concrete structures from water damage relies on preventing or minimizing water penetration. There are two primary strategies for achieving this: applying treatments to the exterior surface (extraneous treatments) or incorporating protective measures during the concrete mix design itself (internal methods). Both approaches require careful consideration and adherence to relevant standards to ensure effectiveness.
II. Extraneous Treatments (External Waterproofing)
Extraneous waterproofing involves applying a barrier to the external surface of the concrete structure. These treatments act as a physical shield, preventing water from reaching the underlying material. Common examples include:
- Paints: Specialized waterproof coatings can be applied to create a protective layer.
- Bitumen Felts: Layers of bituminous felt provide an effective barrier against water ingress.
III. Internal Waterproofing Methods
Internal waterproofing focuses on modifying the concrete mix or incorporating specialized materials to reduce its permeability and prevent water penetration from within. This approach offers long-term protection and is often more durable than surface treatments.
- A. Concrete Waterproofing Admixtures: These admixtures are added during the mixing process, altering the concrete’s properties to enhance its resistance to water. The specific application method and details depend on the manufacturer’s recommendations. When applied to plaster (cement sand mortar), a more detailed procedure is followed:
- Surface Preparation: Before applying plaster, the concrete surface must be thoroughly cleaned and kept consistently wetted for 24 hours. This ensures proper adhesion of the plaster layer.
- Mortar Mix Ratio: The cement-sand mortar mix typically ranges from a ratio of 1:1 to 1:4 by volume, depending on the desired strength and application requirements.
- Admixture Integration: The waterproofing admixture is carefully mixed into the mortar ensuring even distribution throughout the mixture.
- Application Thickness: The plaster should be applied in layers not exceeding 15mm (or as specified by the manufacturer) to ensure proper curing and prevent cracking.
- Curing: Crucially, the plastered surface must undergo continuous curing for a minimum of 14 days, mirroring the curing process for concrete itself. This allows the plaster to fully hydrate and develop its waterproof properties.
- B. Waterproofing by Bituminous or Tar Coating: This method involves applying layers of bituminous (coal tar pitch) or asphalt coatings directly onto the concrete surface. The process requires meticulous preparation:
- Surface Preparation: The concrete surface must be thoroughly cleaned and sandpapered to remove any loose particles, dust, or contaminants that could compromise adhesion.
- First Coat Application: A hot application of coal tar pitch (meeting IS:216 standards) is applied at a rate of no less than 1.5 kg per square meter. It’s vital to ensure the temperature doesn’t exceed 375°F during heating to prevent degradation of the material.
- Second Coat Application: Once the first coat has completely dried, a second application is performed using either coal tar (at least 1.25 kg/m²) or asphalt (at least 1 kg/m²).
- Sand Covering: Immediately after applying the second coat and before it dries, a layer of sand is spread evenly across the surface to cover it completely. This provides additional protection and helps prevent cracking.
- Curing & Backfilling: Sufficient time must be allowed for the final coat to dry thoroughly before backfilling or any other construction activities are resumed.
- C. Bitumen Felt (Tanking): Bituminous felt is commonly used for waterproofing the exterior and interior surfaces of walls and bases, particularly in tanking applications. This method requires adherence to specific standards:
- Material Standards: The bituminous felt must conform to IS:1322, ensuring it meets quality requirements.
- Workmanship Standards: Proper installation is crucial; workmanship should adhere to IS:1609 guidelines.
- Felt Type: Typically, the felt will be either a hessian base or a fibre base, as specified in the project drawings and schedule of items.
- Specialized Firms: Due to the technical nature of this application, it is generally performed by specialized firms with experience in waterproofing techniques.
IV. General Note:
Regardless of the chosen method, it’s paramount that the design, materials used, and workmanship employed all conform to relevant Indian Standard codes where applicable. Proper planning, execution, and adherence to industry best practices are essential for ensuring long-term waterproof protection and maximizing the lifespan of your concrete structures.