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Water is a vital resource, but also a construction
material’s greatest enemy, since rain, groundwater and surface water can cause rapid
and extensive damage to buildings. The solution lies in water-repellent construction
materials with sealing properties such as cementitious slurries modified with dispersible
polymer powders.
Water, in liquid or in vapour
form, is the most destructive weathering element for buildings con-structed 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 water-proof measures must be part
of a whole system
and must interact totally to be completely effec-tive 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 vapour. Traditional
sealing and waterproofing systems include bituminous materials, plastic waterproof-ing
foils and metal tapes for interior and exterior applications. In addition to these
systems, products based on reactive resins, purely dispersion-bound, pasty products
and cementitious waterproofing membranes are now widely used to seal and protect
the outer surfaces of build-ings 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 hydro-static 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 cementi-tious waterproofing membranes are often used as protective
surface-coating systems for struc-tural concrete or to protect building constructions
against aggressive chemicals. The advantages of cement-based 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 vapour permeability compared to most other systems (consequently
no danger of blistering when water vapour per-meates 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 water-proofing slurries
can be applied even to wet or damp mineral surfaces, and their physical prop-erties
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 adhe-sion,
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 wet-curing 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:
1. Standard or rigid mineral
waterproofing slurries Standard, rigid mineral waterproofing slurries are polymer-modified,
prepacked, dry-mix mortars which are gauged with water before being applied as a
slurry by brush, roller or airless spraying, or, if less gauging water is used,
by trowel. Standard or rigid waterproof-ing slurries can only be used for mineral
substrates which are stable, sound and solid, and if there is no risk of crack formation,
movement or dimensional change (e.g. shrinkage). Dispersible polymer powder is used
as a polymeric binder to improve the adhesion of the waterproofing membrane to different
substrates, to improve its cohesive strength, its flexi-bility, its abrasion resistance
and toughness and, last but not least, the water impermeabil-ity and density of
the membrane. Such polymer modified cementitious waterproofing membranes can withstand
water pressure, not only from the positive side, but also, to a limited extent,
due to their excellent adhesion and cohesion, from the negative side, if this is
necessary for a special application. A dispersible polymer powder which confers
a hy-drophobic effect is the preferred type of polymer which should be incorporated
in the dry-mix mortar.
2. Flexible cementitious waterproofing membranes (two-component
systems) Flexible waterproofing membranes are capable of bridging
over small cracks
in the sub-strate. The flexibility of such products depends strongly on the polymer/cement
ratio and, to a lesser extent, on the flexibility of the polymer itself. In addition,
the flexibility of a ce-mentitious 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 diox-ide and other aggressive
products.
3. One-component flexible cementitious slurries In practice,
a major disadvantage of two-component systems is the possibility of mixing errors
due to the lack of knowledge, experience and education of the workers concerning
the appropriate dosage of the liquid component. Wrong doses may be used by chance
or even intentionally in order to save money in the short term. If the dosage of
the liquid dis-persion is too low, the
resulting membrane may not be waterproof
if exposed to hydro-static pressure or will, at the very least, have a reduced flexibility
with a consequent failure of the system. Other reasons for not using two-pack systems
are the difficult and risky handling, the expense and logistics difficulties and
more time consuming and harder work on the job-site when handling two-pack systems.
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. Dispersible polymer powders have been invented
exactly 50 years ago in Germany. In 1957, the German chemical Group WACKER succeeded
in industrially manufacturing the first powder binder as an additive for construction
mortars, marketed worldwide under the VINNAPAS® brand. This invention revolutionized
the entire construction sector, because it finally made pos-sible the production
of one-part, pre-mixed dry mortars that merely needed reconstituting with water
at the building site. To this very day, polymer powders give the construction industry
key benefits, such as major cost savings, not to mention greatly simplified mortar
production and handling. In cementitious sealing slurries, they not only protect
buildings against damage from water penetration, but also against CO2, chlorides,
sulfates and acid rain.
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