Water in liquid or in vapour form, is the most destructive weathering element for building constructed of materials such as concrete, masonry, and natural stone. Waterproofing and damp proofing techniques must preserve a structure’s integrity. Functionality and usefulness for the whole of its life. To eliminate all possible causes of water intrusion, exterior walls 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 of the system, leakage will occur. Possible damage, deterioration. and unnecessary repairs to building facades can be avoided by controlling groundwater and surface water as well as the transport of humidity in the form of water vapour. In addition to protecting the exterior of buildings, a wide variety of waterproofing materials are used in interior application such as bathrooms, toilets, swimming pools, water tanks, etc. Some waterproofing systems are used as protective against the detrimental effect of aggressive substances such as salts and acids transported by water.

2) waterproofing system :

The different components used to cover a building can be classified as

Roofing : an external layer which must prevent water intrusion even in horizontal or slightly inclined elevations.

Below ground waterproofing: materials and measures, which prevent ground water or water hydrostatic Pressure from entering a structure or its components. These systems are usually not exposed to or subjected to weathering or the effect of ultraviolet rays. Examples of belowground waterproofing materials are metal and plastic foils, cementitious waterproofing slurries and bituminous waterproofing materials.

Above ground waterproofing : A combination of materials or systems which prevent water intrusion into exposed structure elements, including protective decorative barrier systems. These materials are not subjected to hydrostatic pressure but are exposed to Weathering and attack by pollutants. Examples of above ground waterproofing are all kinds of paints including cementitious paints, mineral finish plasters and renders.

Damproofing : A material which reduces or prevents water vapour transmission and which is resistant to water vapour or minor amounts of moisture – this system may act as a back up system to primary water proofing materials. Dampproofing material is not subject to weathering or water under pressure.

Flashing : A material or system installed to direct water trying to penetrate  the building Skin tack to the exterior. Flashing is installed as a backup system for a waterproofing or dampproofing system.

Traditional sealing and waterproofing systems. E.g. according to the German standard DIN 18195,include bituminous materials, plastic waterproofing foils and metal tapes.

For interior and exterior applications : In addition to these traditional systems. Products based on reactive resins (e.g. epoxy or polyurethane resins.) purely dispersion bound, pasty products (so-called brush applied waterproofing membranes) and mineral waterproofing slurries (cementitious waterproofing membranes) are now widely used to seal and protect the outer surfaces of building and structural components against the action of water and moisture in the following article cementitious waterproofing slurries and their application will be discussed.

3) Cementitious waterproofing slurries: 

Cementitious waterproofing membranes have been used successfully in Europe for more than 40 years to protect a wide range of buildings and structural components exposed to either periodic or long-term wetting (surface water, seepage water, low hydrostatic pressure (rising damp, soil dampness) 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. basement walls, water tanks, swimming pools , walls and  floors in wet –rooms such as toilets and bathrooms, balconies and terraces (as a waterproofing layer to be tiled over). In addition flexible Cementitious waterproofing membranes are often used as protective surface coating systems for structural concrete (e.g. protection of new and rehabilitated reinforced structural concrete) protection against the penetration of water. Chlorides and free Carbon dioxide thus preventing corrosion of the reinforcement) or to protect building Constructions against aggressive chemicals (sulphates, acid e.g. in wastewater drains).

The advantages of cement based waterproofing membranes are their excellent resistance to water, even if exposed permanently their excellent resistance to long term weathering good scratch resistance good load bearing opacity and much higher water vapour permeability compared to most other systems (consequently no danger of blistering when water vapour permeates through the waterproofing membrane.) Cement based waterproofing slurries are easy to use, are 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 material. Pure and 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 of purely Cementitious slurries, a polymer, in the form of liquid dispersion, is added on the job site or as a redispersible powder already premixed in the dry mix mortar.

Today, several different systems of Cementitious waterproofing membranes or slurries are available:

Standard or rigid mineral waterproofing slurries – FAIRCRETE SB (L): 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 waterproofing 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) a typical composition of such a rigid membrane is used. The water impermeability depends on the cement content the shape and particle size distribution of the fillers, the type of chemical additives used and the amount of redispersible polymer.

Redispersible is used as a polymeric binder to improve the adhesion of the waterproofing membrane to different substrates, to improve its cohesive strength, its flexibility, its abrasion resistance and toughness and, last but not least, the water impermeability 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 redispersible polymer which confers a hydrophobic effect, such as FAIRCRETE SB(L), is the preferred type of polymer which should be incorporated in the dry-mix mortar. Typical dosage is 2 to 10% on total mix weight depending on the quality of the raw materials available, If impermeability against hydrostatic pressure is required, higher amounts of redispersible powder polymer must be used (5 to 10%). It is important to remember that the use of a water-repellent agent will confer water repellent or waterproofing properties on a cementitious mortar but does not make the mortar impermeable to water under hydrostatic pressure. In order to achieve this, the mortar must be very dense , (appropriate filler particle  size distribution), with a low air pore content and contain a sufficiently high polymer content,(the polymer must block the cavities and pores).

3.2) Flexible cementitious waterproofing membranes (two-component systems)

In addition to the traditional rigid waterproofing membranes, developments in Europe in the late 1970s led to introduction of flexible waterproofing which, to a limited extent, are capable of bridging over small cracks in the substrate (up to approx. 1mm wide). 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 cementitious waterproofing membrane depends on the environmental conditions to which it is exposed. These conditions can be simulated by laboratory test methods, using different storage conditions. When a flexible cementitious waterproofing membrane is applied and store under dry conditions, especially at high temperatures and on absorbent substrates, only a minor part of the cement of this thin layer system is hydrated. Therefore the actual effective polymer/cement ratio is higher than the theoretical value and the whole system is very flexible, being dominated by the polymeric binder. When later the cement has fully hydrated under wet or humid conditions and the system achieves its final properties, its tensile strength increases, and the elongation and flexibility decrease. Consequently, the mechanical characteristics of cementitious membranes can only be compared if the cement is fully hydrated. This means that, in order to check the retained flexibility of a cementitious membrane after lone immersion in water, the membrane must be tested in the laboratory under conditions, which allow the cement to hydrate fully. This is important to avoid failures in practice due to insufficient flexibility caused by later complete hydration of the cement.

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 product.  Two – component, flexible cementitious waterproofing slurries are available in two different forms.

As a two-pack system composed of a prepacked dry-mix mortar based on cement, fillers and other additives plus a liquid dispersion in the second pack. This is the system most commonly used today for two component flexible waterproofing slurries.

As a system based on a wet premix of an aqueous dispersion, fillers and additives.

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 dispersion is too low, the resulting membrane may not be waterproof if exposed to hydrostatic 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 handing the expense and logistics difficulties (e.g. the need for additional containers, the problem of their safe disposal, storage and transport of liquid dispersions which could freeze or deteriorate throughout microbiological attack) and more time consuming and hard work on the job site when handing two pack systems. Because of the many disadvantage 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.

FAIRMATE waterproofing systems has developed special redispersible powders with very low glass transition temperatures, low water absorption and high water resistance in order to be able to formulate one- component, flexible, and cementitious waterproofing slurries.

The higher cost of such products, due to the high dosage of the redispersible Powder, is compensated for 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 on the job-site, higher productivity on the job site, etc.

4) Brush applied ready to use dispersion bound waterproofing slurries : 

Ready to use dispersion bound waterproofing slurries form membranes with extremely high and long- lasting flexibility and very adhesion to all inorganic and organic substrates. They are flexible cementitious slurries are mainly used if very flexible waterproofing membranes are required and for substrates which are difficult to stick to (e.g. bitumen Gypsum, plywood, etc). The membranes formed by these slurries have a relatively low cohesive strength, show some softening after prolonged immersion in water and are liable to form blisters. Since they form impermeable films by physical drying, these products should not to be applied under conditions of high humidity and are unsuitable for exterior and floor applications and for applications where permanent immersion in water is involved. In addition there are disadvantages concerning the logistics with liquid or pasty products, such as risk of bacterial infection, transport of water and expensive packaging.

5) Installation and application of cementitious waterproofing slurries : 

Before applying cementitious systems, substrates must be free from dirt, laitance, release agents ,and all other foreign materials. The substrate must be sound and solid and all blowholes, cavities and cracks must be filled with appropriate cement mortars. Waterproofing cementitious slurries, even the flexible types, should not be applied over construction joints, wall –to-wall and wall-to-floor joints, which should be sealed with either an elastic sealant (e.g. silicone sealant) or an embedded elastic plastic foil.

Cementitious waterproofing membranes can be applied by brush, roller, trowel or by airless spraying. Usually a brush is used to apply slurry like mortar, which is why these products are very often called cementitious waterproofing slurries.

All cementitious waterproofing slurries must be applied in such a way that after drying a layer at least 2mm thick results. This is generally obtained only with multiple coats, usually two or three (typical drying time between coats is 2 to 5 hours). To ensure the impermeability of the membrane, at least 2 coats must be applied, even if a layer of 2mm or more could be applied in one step e.g. by trowelling the slurry at 3mm thickness. This is because pores and micro cracks may have been formed or left within the first coat and these are sealed by subsequent coats. It is not necessary to keep the freshly applied polymer modified slurry moist or to wet-cure it, but it is important to ensure that it dries slowly.  

Exposure to rain or excessive sunshine must also be avoided in the first few hours. Or even better, for the first day after application.  Permanent hydrostatic pressure is expected a suitable water proofing slurry should be applied to the positive side of the structure to be waterproofing i.e. to the side of the structure facing the expected source of the water.

If waterproofing membranes are to be used for drinking water tanks, local restrictions concerning the use of with drinking water must be respected.

6) Technical requirements and performance of waterproofing slurries :

Technical requirements of waterproofing membranes (e.g. concerning flexural strength, compressive strength, tensile strength, elongation at break, water vapour permeability, Crack over bridging capability, water absorption impermeability under hydrostatic pressure, adhesion to the substrate are defined based on more than 40 years of particle experience in Germany. If multiple layer systems are used in order to waterproofing a structure, the modulus of elasticity of each coating should be lower, or at least not higher, than the modulus of the layer below it in order to prevent crack formation and failure of the system.