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Making Buildings Water Resistant

 

A key element of sustainable building is preserving the structure by preventing water seepages. Various waterproofing technologies are developed as mechanism to maintain a building and also to address the aesthetic elements.

Most of the building materials are very porous and have surface hydroxyl groups. These hydroxyl groups attract water because of the hydrophilic nature and similarity with the structure of water. Therefore, most of the building material easily wet and absorb water in the pores. The size of the water molecule is 0.18cm (nanometer 10-9m i.e. .00018 microns. The size of the pores in most of the building materials range from 5 to 200cm. The size of most of the pollutants like acids, chlorides and sulphates would range between 1 to 2cm. Even with the dense concrete and stones the pore size is much larger than water allowing easy entry with the hydrophilic nature of the building material.

Waterproofing enables both preventing water passage and resisting hydrostatic pressure which can be achieved by – waterproofing from the positive (exterior) side, negative (interior) side or from within the concrete itself (integral systems). Although the oldest and most widely used positive-side technology is sheet membrane waterproofing, many construction projects around the globe have used integral crystalline admixtures to waterproof concrete. Integral systems block water passage from any direction by working from the inside out, making the concrete itself the water barrier.

Different types of waterproofing systems
Kevin Yuers, Vice-President responsible for Product Development, Technical Services and Operations of the Kryton Group of Companies, Vancouver, BC, discusses below the substantial advancements in both membranes and crystalline admixtures.

Sheet membrane systems
Historically, hot-applied sheet systems – known as built-up bituminous membranes – have been used for below-grade concrete waterproofing. These sheets were made from alternating layers of bitumen and felt. When heated, traditional bitumen – both coal tar pitch and asphalt – releases volatile organic compounds (VOCs) and potentially carcinogenic fumes.

Since the early 1990s, the bitumen system’s popularity has fallen due to an increasing number of bans on its use by governmental and regulatory agencies. Substantial steps have been taken by product manufacturers to replace these membranes.

Polymer-modified bitumen has evolved from the original bituminous sheet systems, offering a safer and cold-applied alternative. Cold-applied polymer-modified bitumen is a sheet membrane composed of polymer materials compounded with asphalt and attached to a polyethylene sheet. The polymer is integrated with the asphalt to create a more viscous and less temperature- sensitive elastic material compared to asphalt on its own. These sheets are self-adherina, and eliminate the harmful toxins typically associated with asphalt adhesion. They also increase tensile strength, resistance to acidic soils, resilience, self-healing and bondability.

Despite such advancements, disadvantages persist. Their field fabrication requires intensive labour and carefully supervised installation.

Installation can be challenging as membranes require sealing, lapping and finishing of seams at the corners, edges and between sheets. Additionally, sheet membranes must be applied to a smooth finish without voids, honeycombs or protrusions. Because the membrane can puncture and tear during backfilling, protection boards also need to be installed. Sheet membranes pose other limitations as well. They are challenging to use in vertical applications and difficult, if not impossible, for blind wall applications. They are often inaccessible for repairs after installation.

Performance and durability can also be issues. Performance depends on surface adhesion and proper seam lapping. Materials are strongest on the first day following installation, after which they gradually deteriorate.

Although polymer-modified bitumen is an improvement over the earlier hot-applied ones, they still present challenges, including poor resistance to ultraviolet radiation, the need for solvent-based primer and adhesives and an air temperature warmer than 4°C (25°F) during installation.

Careful installation practices must also be followed. Sheets can de-bond if they are not promptly covered after installation, the top edges are not sealed, the primer is incorrectly applied or if tie-holes are not flush with the concrete surface.

In spite of all these drawbacks, sheet membranes have been the industry norm in waterproofing for many years –they still hold the majority of the market share. Their continued use is due to impact resistance, toughness and overall durability compared to other membrane options.

Thermoplastic membranes
Thermoplastic polymers have led to the creation of thermoplastic membranes. These membranes are composed of polyvinyl chloride (PVC), chlorinated polyurethane or chlorosulfonated polyethylene, with glass fibre-reinforced PVC being the most popular membrane type.

Thermoplastic materials soften when heated and harden when cooled, so sheets can be attached with solvent-based adhesives or by heat-welding at the seams – a significant advantage over field-fabricated seams. Thermoplastic membranes also effectively resist chemicals and hydrostatic pressure.

Despite these advantages, there are drawbacks. Thermoplastic membrane properties change depending on the temperature. The PVC deteriorates if it is in contact with hydrocarbons. Installation still demands the use of solvent-based primer and adhesives and any asphalt-based protection boards cannot be placed directly on the PVC membranes. In addition, the concrete must have a “floor quality” steel trowel finish to ensure good adhesion.

Thermosetting membranes
Thermosetting membranes (i.e. vulcanized rubber) are more resistant to heat, solvents, general chemical attack and creep than thermoplastic membranes, due to the vulcanization of butyl, ethylene propylene diene monomer or neoprene rubber.

However, as thermosetting materials harden permanently when heated, these sheets can only be attached using solvent-based adhesives on the seams. The movement after application is very restricted. Also, because the seams between sheets are field-fabricated, they never attain the base material’s tensile strength. Thermosetting membrane sheets tend to stretch and are difficult to install on vertical surfaces. They can disband or blister if a negative vapour drive is present because they do not breathe. They require the use of solvent-based primers and adhesives which is another drawback.

Clay systems (bentonite)
For more than 75 years now, bentonite waterproofing has been employed and today still remains a popular method. Its effectiveness is based on the properties of impure clay, which swells to block water. Bentonite is versatile and comes in various forms from prefabricated panels to trowelable mixtures.

Clay systems are excellent for waterproofing but need sufficient hydration for success – and in some applications this can be difficult and unreliable. First, high hydrostatic pressure is required for complete hydration of the clay molecules. Hydration must occur immediately after installation and backfilling. It must also take place in an adequately confined area to avoid lifting or cracking the concrete slab. Bentonite can self-heal, is non-toxic and is relatively easy to install, but is rarely minimal in places where leaking risk must be minimal and humidity control is necessary. Bentonite materials are weather-sensitive and not resistant to soil chemicals (e.g., brines, acids or alkalines), which ultimately decreases their ability to thoroughly waterproof structures.

Bentonite systems cannot be installed during rainfall while Groundwater level is fluctuating or in areas with constant wetting and drying cycles because the clay will deteriorate. Installation is also not advised in places with free flowing water that would wash away clay. Once installed, bentonite is difficult to remove, so options for future repair or replacement are limited. Bentonite sheets are most beneficial for blindside wall applications as they can be nailed directly to the foundation walls.

Liquid-applied membranes
Liquid-applied membranes can be applied with a brush, spray, roller, trowel or squeegee, and usually contain urethane or polymeric asphalt (hot- or cold-applied) in a solvent base. These membranes are usually applied on the positive side of set concrete and have high elastomeric properties. More recent technologies have also made negative-side applications possible.

Successful waterproofing with liquid-applied membranes depends on proper thickness and uniform application. They call for skilled, experienced labour to apply them, a clean and dry substrate – which can often be a construction environment challenge – a protection layer before backfilling, properly cured concrete to avoid problems with adhesion and blistering and, on horizontal applications, a sub-slab. Liquid-applied membranes deteriorate when exposed to UV radiation and cannot withstand foot traffic. The liquids themselves also contain toxic and hazardous VOCs.

Although liquid-applied membranes work well on projects with multiple plane transitions, intricate geometric shapes and protrusions, they are typically only used when prefabricated sheets do not work.

Admixtures
For the last three decades, a new type of waterproofing is being used around the globe. These integral admixture systems are added at the batching plant or onsite, and react chemically within the concrete. Instead of forming a barrier on the positive or negative side of concrete, they turn the concrete itself into a water barrier. Integral concrete waterproofing systems can be densifiers, water repellents or crystalline admixtures.

Densifiers react with the calcium hydroxide formed in hydration, creating another by-product that increases concrete density and slows water migration. They are typically not characterized as waterproofing materials or repellents because they have no ability to seal cracks and joints. Concrete under hydrostatic pressure requires additional waterproofing methods to protect it from damage and deterioration.

Water repellents are also known as “hydrophobic.”

These products typically come in liquid form, and include oils, hydrocarbons, stearates or other long-chain fatty acid derivatives. Although hydrophobic systems may perform satisfactorily for damp-proofing, they are less successful at resisting liquid under hydrostatic pressure. Pre-curing and post-curing stresses because cracking in any concrete, which creates pathways for water passage. So the effectiveness of water repellents is highly dependent on the concrete itself.

Crystalline admixtures
Crystalline-based systems typically come in a dry, powdered form and are hydrophilic in nature. Unlike their hydrophobic counterparts, crystalline systems actually use available water to grow crystals inside concrete, effectively closing off pathways for moisture that can damage concrete. They block water from any direction because the concrete itself becomes the water barrier.

In contrast to water repellents, crystalline technologies enable self-sealing. The admixture is a blend of cementitious and proprietary chemicals that actually work with the available water in concrete to form insoluble crystals. These needle-like crystals grow until all pores are blocked and no water can penetrate the concrete. The crystalline formula can allow concrete to self-seal hairline cracks up to 0.5mm (0.02 in.), even years after the original construction.

Concrete treated with these admixtures contains chemicals that lie dormant within. If a crack forms, any water influx causes more crystals to grow, re-blocking and sealing the passage against water and waterborne contaminants. Whenever new water enters the concrete through changing water levels or new cracks, crystals continue to grow and seal the concrete. The crystals within the concrete are impervious to physical damage and deterioration; there is no danger of punctures, tears or seam leaks. As a result, a building’s durability increases when crystalline admixtures are used.

In addition to promoting and enhancing the natural hydration process of cement, these systems are highly versatile, useful and reliable for a wide range of applications. For example, concrete treated with crystalline admixtures is suitable for complex architectural designs. As architectural protrusions do not pose any waterproofing challenge, any type of concrete structure – vertical, horizontal or shaped –can be securely waterproofed.

Concrete waterproofed with crystalline admixtures affords other benefits, too. It contains no VOCs and can be completely recycled when demolition occurs. Membranes do not have to be separated from the concrete, waterborne contaminants are not present in the concrete, and petroleum-based materials are not left behind to leach into soil.

Additionally, crystalline admixtures offer installation advantages. Unlike traditional membrane waterproofing, which tends to be labour-intensive and expensive, crystalline technology decreases installation and maintenance costs and is easy to handle – admixtures can be shipped in dissolvable, palpable bags that are thrown into the concrete batch during mixing. This speeds up the construction schedule and decreases labour costs by combining steps with concrete placing.

Integral crystalline waterproofing systems should not be used in applications under constant movement. During the crystallization process, crystals align in a three-dimensional array that breaks when subjected to excessive movement. Areas that require flexibility and face recurring movement – such as plaza decks or rooftops – would be better waterproofed another way.

PoGymer systems
Ajay Mohta, General Manager, Construction Accessories Division, Supreme Industries Ltd explains that polymer-based waterproofing agents are known to be one of the best for providing effective and long term solution, as polymers due to their unique properties do not disintegrate and guarantee a leak-free structure.

Polymeric membrane
“Demand for developing waterproofing solutions to solve the leakage problems in factories and offices had been increasing. They were not pleased with the current waterproofing systems available in the market.

About a year back, our R&D team started working on a project to develop a composite of various polymers cross linked and fused resulting in this exclusive high performance membrane. This new generation high performance, composite polymeric membrane is a cost-effective solution for waterproofing of basements and roofs. It is a versatile material, capable of retaining the dryness of concrete, masonry, metal & wood structures and is resistant to salts, alkalis and most acids. It is a quick and easy-toapply system, ensuring hassle-free maximum productivity for applications like concrete roof waterproofing, basement waterproofing and also waterproofing of bathrooms & ‘terrace gardens,” says, Mohta.

Durable and lightweight, polymeric membrane is non-deteriorating, puncture resistant and is available in length up to 50m. In comparison, bitumen disintegrates after it comes in contact with water. Further, over a period it catches fungi and also starts melting during summer, thus lowering its puncture resistant strength.

“The striking feature about Supreme Industries’ polymeric membrane is that it has a very good puncture resistance of 199 N (Test method – ASTM E154: 1999) and does not deteriorate over a long period. None of the waterproofing solution systems provide any added advantage except waterproofing whereas polymeric membrane is also an excellent insulating material,” adds Mohta. Any roof treatment has to contend with the unrelenting assault of surface expansion and contraction due to daily / seasonal temperature changes. Unlike polymeric, other treatments have a tendency to absorb moisture and conduct heat. Its ‘K’ value does not deteriorate. Its inherent closed cell structure ensures truly effective thermal insulation and waterproofing virtually for a lifetime.

India being a tropical country has diversity in climates. When the ambient temperature varies between 0 to 50°C, the overlying treatment is called upon to withstand a corresponding variation of 1 to 65°C. Polymeric membrane meets these challenges with complete and effortless ease and can withstand temperature ranging from 40 to 115°C.

Roof treatments have to withstand more than just surface expansion and contraction. Like structural movements, for example or the setting of the building with time. Sudden drops in temperature results into thermal shocks. Also vibrations caused by rail/road traffic and overflying aircraft. Polymeric membranes are fracture, crumble, shatter and abrasion proof and resistant to most corrosive chemicals. This concrete roof and basement waterproofing product is specially designed to withstand the hot and humid Indian conditions.

Polymer seals
Ina major breakthrough, the use of polymer resin made of rubberized asphalt with special adhesives in the form of gel, has become a multi-application waterproofing material. This gel seeks out leaks, expands in contact with water to repair damaged layers and absorbs movement and vibration to minimize damage and separation. Tough, elastomeric, flexible and self-sealing, it works in wet conditions, underwater and/or cold environment. Effective on multiple material surfaces and compatible with other waterproofing products, it is easy to maintain. Being an eco-friendly composition, it is non-solvent material, chemical resistant, durable and stable in a wide range of climates.

All materials, including concrete and waterproofing material have their own coefficient of thermal expansion, contracting and expanding on the central axis according to temperature change. Since the concrete joint that contributes the most water leakage is located at the farthest point from the central axis, it has the largest movement range. The gel flexibly
responds to these contractions and expansions to stop water leakage.

In the repairing process, the polymer gel can be injected to seal the damage.

Nanotechnology systems
The waterproofing product data suggests that Silane based waterproofing products are desirable for long-term performance. Silanes and Silane/Siloxanes are known as new class of waterproofing products. These products are used in USA and Europe for last 30 years. However, only last few years they became available in India.

Silanes are monomeric materials. The products used for waterproofing are known as alkylalkoxysilane having two types of groups – (a) alkyl group, R’ and (b) alkoxy group, OR, which are reactive to the most building materials.

Most building materials contains hydroxyl (OH) group. These OH groups can chemically react with alkoxy groups of Silane forming permanent siloxanes bonds with the substrate. The alkyl group R’ provides hydrophobicity (water repellency) to the surface. Therefore, these types of products impart water repellency by modifying surface characteristics from hydrophilic to hydrophobic.

Beside superior performance silanes, usage is limited on a worldwide basis because of high cost 35 to 60 US cents  per sqft. Also, solvent’s flammability and toxicity imposes limitations to easy applications.

Recently Zydex Industries in India has developed a waterproofing product which provides all three most desired properties. It is based on nano technology; it provides molecular level hydrophobicity to inorganic substrate. It is eco-friendly, because it is applied in water solution and VOC per applied M2 is less than 20% compared to solvent based silanes. The product is based on organosilicon chemistry, hence reacts with the inorganic substrate surface and provides long service life of 20-30 years.

Apart from the resistance they can impart to water absorption, all systems and waterproofing material now also address low environment and health risk and a long time UV stability.