Concrete is porous and, if not waterproofed, absorbs water that can cause cracks, water-borne contaminants and chemicals that can cause deterioration. If you want to protect your concrete and ensure it has a long, serviceable life, waterproofing is essential.
But how? What’s the best method and the best material?
To make concrete really waterproof — which means both preventing water passage and resisting hydrostatic pressure — you can waterproof from the positive (exterior) side, negative (interior) side or from within the concrete itself (integral systems). Although the most widely used positive-side technology is sheet membrane waterproofing, its failures and limitations are also common and costly. Since the 1980s, 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.
It can be difficult to keep up with advancements in both membranes and crystalline admixtures — and there have been substantial advancements in both technologies. Here’s a summary that can help make the choice more clear.
Sheet membrane systems
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-adhering 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. 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 must also be installed.
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.
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 has been 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 dampproofing, they are less successful at resisting liquid under hydrostatic pressure. Precuring and post-curing stresses cause 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. The crystalline formula can allow concrete to selfseal hairline cracks up to 0.5 mm (0.02 in.), even years after the original construction. It contains no volatile organic compounds (VOCs), and can be completely recycled when demolition occurs.
Additionally, crystalline admixtures offer installation advantages. Unlike traditional membrane waterproofing, which tends to be labour-intensive and expensive, crystalline admixtures can be shipped in dissolvable, pulpable 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.
Kevin Yuers, vice president, Kryton International is responsible for product development and technical services.
Source: Construction Business
