Water, in liquid or in vapor form, is the most destructive weathering element for buildings constructed of materials such as concrete, masonry, and natural stone. Waterproofing techniques therefore must preserve a structure’s integrity, functionality and usefulness for the whole of its life. Due to the harsh conditions of the monsoon, there’s a special challenge for waterproofing systems in India. To eliminate all possible causes of water intrusion, the exterior walls, the roof and the basement of a building must be completely covered with waterproof material. All waterproof measures must be part of a whole system and must interact totally to be completely effective in preventing the ingress of water.
Should one component of the system fail or not interact fully with all other parts, leakage can occur. Possible damage, deterioration and unnecessary repairs to building facades can be avoided by controlling groundwater, rainwater and surface water, as well as the transport of humidity in the form of water vapor.
Traditional sealing and waterproofing systems include bituminous materials, plastic waterproofing foils and metal tapes for interior and exterior applications. In addition to these systems, products based on reactive resins, purely dispersionbound, pasty products and cementitious waterproofing membranes are now widely used to seal and protect the outer surfaces of buildings and structural components against the action of water and moisture.
Cementitious waterproofing membranes have been used successfully to protect a wide range of buildings and structural components exposed to either periodic or long-term wetting, low hydrostatic pressure or, in combination with appropriate engineering, even high hydrostatic pressure. Cementitious membranes are used for waterproofing wet rooms and water tanks and, due to their excellent weathering resistance, also for exterior surface protection. Typical applications are the sealing and waterproofing of e.g., terraces, basement walls, water tanks, swimming pools, walls and floors in wet-rooms such as toilets and bathrooms. In addition, flexible cementitious waterproofing membranes are often used as protective surface-coating systems for structural concrete or to protect building constructions against aggressive chemicals.
The advantages of cementbased waterproofing membranes are their excellent resistance to water, even if exposed permanently, their outstanding resistance to long-term weathering, good scratch resistance, good load-bearing capacity and much higher water vapor permeability compared to most other systems (consequently no danger of blistering when water vapor permeates through the waterproofing membrane).
Cement-based waterproofing slurries are easy to use, non-toxic, provide a monolithic, fully bound, joint-free surface and can easily be applied to substrates with complex surface shapes. In contrast to other systems, cementitious waterproofing slurries can be applied even to wet or damp mineral surfaces, and their physical properties are less temperature-dependent than bitumen based materials.
Simple cement-based slurries are still used for protection against surface water, but they are not suitable to seal against water under hydrostatic pressure. In order to improve the poor adhesion, the poor water impermeability and the extremely low deformability and flexibility, a polymer must be added to the system. The use of special additives such as water retaining agents, thickeners and rheological additives, combined with a polymeric binder, confers excellent workability and ensures that wetcuring of the applied slurry is unnecessary.
As polymeric binder, dispersible polymer powders have proved their value. Dispersible polymer powders are thermoplastic, plasticizer-free polymers derived primarily from vinyl acetate and ethylene. When water is added, these spray-dried dispersions “redisperse,” while retaining all the properties and functions typical of a liquid polymer dispersion. As the mortar sets, flexible polymer bridges are formed between the brittle mineral constituents of the mortar, producing a polymer film that acts as an organic binder. This greatly improves the mortar’s adhesion to a wide range of substrates and increases the system’s flexibility.
Today, several different systems of cementitious waterproofing membranes or slurries are available.
Standard or Rigid Mineral Waterproofing Slurries
Flexible Cementitious Waterproofing Membranes (Two-component Systems)
In addition, the flexibility of a cementitious waterproofing membrane depends on the environmental conditions to which it is exposed. Flexible, cementitious waterproofing membranes are applied to substrates expected to be subject to shrinkage, vibration, movement, stress and crack formation and to substrates which are difficult to stick to, such as wood, steel, aerated light weight blocks and gypsum. Due to their high polymer content, these coatings have a low coefficient of diffusion and are resistant to chemicals such as chloride ions, sulphate ions, carbon dioxide and other aggressive products.
One-component Flexible Cementitious Slurries
Because of the many disadvantages of modifying a mortar with a liquid dispersion as mentioned above, the so-called one-component flexible cementitious slurry in the form of a premixed dry-mix mortar is increasingly being used.
Dispersible polymer powders are employed, with very low glass transition temperatures, low water absorption and high water resistance in order to be able to formulate one-component, flexible, cementitious waterproofing slurries.
The higher cost of such products, due to the high dosage of the dispersible polymer powder, is compensated by the advantages of having a one-component, polymer-modified, dry-mix mortar, e.g., low-cost logistics and packaging, safety and reliability for the application by excluding mixing errors, and higher productivity on the job-site.