Waterproofing

Waterproofing Systems

Waterproofing systems can be generally classified into integral, preformed membrane and liquid-applied membrane systems (Figure 1). Each system has their advantages and disadvantages when used in different parts of the building [1].

Integral Systems

Integral systems will reduce the permeability of the concrete by introducing water-reducing agents, pozzolanic products, organic binders or pore blocking additives [2]. These systems do not employ the use of any coating layer to keep out water. Structures using integral systems are constructed with high-quality concrete. Cracking should be controlled to prevent the penetration of moisture to an acceptable level. Water penetration is minimized solely by the ability of the structure itself. The types of integral system used in Singapore (Figure 2) are crystalline waterproofing, admixtures and waterproofing screeds.

Crystalline Waterproofing

Crystalline waterproofing systems are made with Portland cement, fine quartz or silica sand, organic and inorganic sodium and/or calcium salts and/or stearates [3]. Crystallization systems are only effective on concrete that is sound and free from defects. Crystallization systems act as penetrating sealers. Chemical reactions take place at the coating/concrete interaction surface. These systems are coated onto the concrete surface, and normally contain chemicals that diffuse through water held in the capillaries of the concrete. The chemicals react with free lime to form chemical complexes that physically block the passage of water.

Water acts as a catalyst with free lime (calcium hydroxide) and sodium to form insoluble minerals like sodium silicate. Crystals are formed when water interacts with sodium silicate. By osmosis, sodium silicate forms will fill up the pores of inner concrete surfaces, in the process reducing permeability.

Crystals will continue to grow and penetrate into the concrete in the presence of water, free lime and the active chemicals. The crystals have fixed size air spaces which are smaller than water molecules, thus preventing the water molecule to pass through. If crystallization systems are applied to concrete that is already watertight; they will remain on the surface of the concrete within the coating. If water penetrates at a later stage, the chemicals will activate and migrate into the cracks.

Admixtures

Admixtures are added to concrete to improve its waterproofing abilities. To achieve water-tightness in concrete, a small amount of calcium, aluminium or other stearates are inter-grinded to form cement admixtures.

Cement admixtures are generally blended at the manufacturing plant. Admixtures are usually added to concrete as it is being mixed. Admixtures are generally used to effect workability, strength and setting time more than water-tightness.

This allows complete hydration and the promotion of internal curing, allowing a reduction in shrinkage, and therefore providing a denser, higher strength and better water-resistant product.

Waterproof Screeds

Waterproof screeds systems are formed by using portland cement, silica sand, water and a water repellent such as stearic acid [4]. Waterproof screeds are usually combined with latex such as acrylics, polyvinyl alcohol and/or styrene butadiene to make the systems flexible.

Preformed Membrane Systems

Preformed membrane systems are made of flexible or elastomeric materials that form a physical barrier when applied over the surface of a structure [5]. The methods of fixing preformed membrane systems include self-adhesives, adhesive bonding, chemical welding, hot air welding and mechanical fixing. The preformed membrane system should be effectively bonded/mechanically fixed to the concrete substrate. This should be carried out according to the manufacturer’s instruction.

Preformed membrane systems are manufactured off-site. This ensures uniform application thickness throughout an installation. Preformed membrane systems installations involve multiple seams and laps, and are not self-flashing at protrusions and changes in plane. Seams are lapped and sealed for complete waterproofing. However, in small confined areas such as internal wet areas, vertical installation and transitions to horizontal areas become difficult. Because of this limitation and the large number of protrusions in internal wet areas, this system is seldom used in internal wet areas.

Liquid-Applied Membrane Systems

There are many different types of liquid-applied membrane systems available in the local construction industry. However in Singapore, only four systems are extensively used in wet areas (Figure 3). The systems are cementitious waterproofing, acrylic-based, polyurethane liquid-compound and rubberised-based systems.

Cementitious Waterproofing System

Cementitious waterproofing system contains a base of portland cement, with or without sand, and an active waterproofing agent [3]. There are four types of cementitious waterproofing systems (Figure 4) namely metallic, capillary/crystalline, chemical additive and acrylic modified system. All cementitious systems are similar in application and performance, but they repel water differently by the proprietary additives of a manufacturer’s formulations.

Cementitious waterproofing systems are available in a wide range of packaging. The product comes in a pre-packed form in powdery format, in which the cement powder is mixed with latex polymer. The polymer will give adhesion and also prevent cracking from occurring due to its elasticity. It cures to form an elastomeric impermeable membrane as shown in Figure 5.

The product may be pre-mixed with sand and cement in pails, or chemicals and iron may be provided in separate containers and added to the sand and cement mixture.

Metallic Systems

Metallic materials contain a mixture of sand and cement with finely graded iron aggregate or fillings [3]. They form a type of slurry for application when mixed with water. The water acts as an agent, permitting the iron mixings to oxidize. Oxidization of such mixings will enable the materials to expand and effectively sealing up a substrate, thus preventing further water transmission.

Capillary/Crystalline Systems

Capillary/Crystalline systems are mixtures of cement and sand in combination with proprietary chemical derivatives in dry or liquid form [4]. Other than waterproofing, the chemical additives are able to penetrate into the concrete wall or slab and react with the calcium hydroxide and available capillary water present to form crystalline structures within the concrete itself. These crystalline structures block transmission of water through the substrate, adding additional water repellency to the envelope components.

Chemical Additive Systems

Chemical cementitious systems are a mixture of sand, cement and proprietary chemicals (inorganic or organic), which when applied to masonry or concrete substrates provide a watertight substrate by chemical action [4]. Proprietary chemicals are unique to each manufacture, but typically include silicate and siloxane derivatives in combination with other chemicals. Chemical systems become an integral part of the substrate after application.

Acrylic Modified Systems

Acrylic modified cementitious systems add acrylic emulsions to a basic cement and sand mixture [4]. These acrylics add waterproofing characteristics and properties to in-place materials. Acrylic systems are applied in two trowel application. The mesh adds some crack-bridging capabilities to acrylic installations. However, since the systems bond tenaciously to concrete or masonry substrates, the movement capability is limited.

Acrylic-based System

This is a highly flexible liquid-applied emulsion (Figure 6). It has good tearing strength due to fibre-glass reinforcement. Most formulations consist of a combination of emulsified acrylic resin, fillers (calcium carbonate), wetting agents (surfactants), bacteria killers and plasticisers.

This system is ultra-violet resistant and comes in a range of colours. This system however requires a longer curing time. Many contractors do not like to use acrylic-based systems as the waiting time interrupts their work and cause a lot of inconvenience. This is one of the main reasons why acrylic-based systems are rarely used in internal wet areas.

Polyurethane Liquid-Compound System

Polyurethane Liquid-Compound polymerizes in air to form a seamless membrane which is fully bonded to the structure (Figure 7). It forms a tough monolithic barrier to moisture, has low permeability and high flexibility.

Polyurethane Liquid-Compound includes the coal-tar or pitch modified polyurethane systems. Coal tar uses the residue left behind in coal-fired furnaces, which have very similar properties to bitumen and therefore lends well to waterproofing components. Unlike bitumen, it is compatible and accepts modification with a higher polymer such as epoxy and urethane to improve its physical properties.
Coal tar urethanes are used more commonly in Singapore for wet areas as they are available as a single-pot, air-curing material, applied by brush or squeegee and is normally black in colour.

This liquid compound is vapour permeable. It allows entrapped moisture to escape. It is also self flashing against protrusions and penetrations in wet areas. It is durable, staying flexible without creep, flow or embrittle. The system is also easy to repair as the new material adheres readily to damaged surfaces.

This liquid compound however has low ultra-violet resistance. It is also solvent based, requiring ventilation and a longer curing time (approximately 3 days). This system is not usually used in internal wet areas because of the toxic content. There is usually lack of ventilated working space in internal wet areas.

Rubberised Based System

This system is generally classified under polyisoprene as it consists of both natural and synthetic rubber. In its original state, they include a natural rubber latex-based coating using the same resins as those used for surgical gloves. They also include synthetic rubbers such as butyl-rubber. Styrenebutadience rubber coatings are formulated for the less critical applications.

These systems are available as a single-component liquid emulsion system for application by brush or rollers onto the concrete substrate. These systems are generally water-based and usually available in black colour. Rubber-based coatings are recognised by their inherently high recovery rate upon elongation, giving it a spring-back effect similar to those of a rubber band. Rubber polymer is added to result in a product that has outstanding elastic, adhesion and saturation properties. It is tough, flexible and non-toxic, making it suitable for use in potable water conditions. This waterproofing system requires about three days to cure.

References

[1] Hewitt, P (1997). Waterproofing concrete. Concrete (London), Volume 31, issue 3, pp. 14-17.

[2] Day, R.W. (1996). Moisture penetration of concrete floor slabs, basement walls, and flat slab ceilings. Practice Periodical on Structural Design and Construction, Volume 1, Issue 1, pp. 104-107

[3] Kubal, M.T. (1999). Construction waterproofing handbook. McGraw-Hill, New York.

[4] Good industry practices, waterproofing for internal wet areas. (2001). Building & Construction Authority.

[5] Ko, W.E. (1989). Cement based waterproofing coating for basements and elastomeric acrylic rubber based waterproof coating for walls. CIDB-HDB Waterproofing Seminar: Waterproofing in tropical climate/Organised by the Construction Industry Development Board; supported by National Construction R&D Advisory Board, Singapore.