There are many reasons why durability is important for commercial construction and the waterproofing of covered podiums and plaza decks, green roofs, balconies and terraces. Most of these public areas need to withstand foot traffic, vehicles and equipment transport. In all cases, especially with roofs, specifiers need to ensure there is a reliable, highly durable membrane sealing the surface and any design features to provide long-term water protection.

Commercial builders, designers and architects can choose from numerous different types of waterproofing products. Liquid-applied is typically preferred when conformation to the given site layout and/or speed of installation are critical. There are two types of liquid waterproofing—cold-applied and hot-applied—and each of them has its own set of features and benefits. In addition, the total amount of material needed to provide a reliable waterproofing layer should be considered.

So, which type of liquid waterproofing is more durable? After looking at the durability factors in waterproofing, this article will explore the differences between cold and hot-applied waterproofing, concluding which liquid waterproofing type is recommended based on those all-important durability factors.

The Durability Factors in Liquid Waterproofing

There are six major criteria that should be considered when assessing the durability performance of a component product and system overall, five of which are defined through ASTM International standard testing methods. Formerly known as the American Society for Testing and Materials, ASTM is a standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems and services.

The six testing criteria for vulcanized rubber and thermoplastic elastomers (the materials that hot-applied and cold-applied liquid waterproofing solutions are made of, respectively) are as follows.

1. Tensile (Tension) Strength (ASTM D412)

The ability to withstand tensile forces. Tensile strength measures the stress required to stretch the material to the point where it breaks. It can be used to evaluate the maximum amount of tensile force that a material can be subject to before failure.

2. Tear Resistance or Tear Strength (ASTM D624)

The resistance to tearing action, including the force to initiate tearing of the materials or tear propagation. With a waterproofing application, the force to initiate the tearing is particularly important.

3. Adhesion to Concrete (ASTM D4541/ASTM D7234)

The greatest perpendicular force a surface area can bear before a section of material is “pulled off” or detached. How well the material adheres to the concrete and maintains after water immersion is very critical with liquid waterproofing.

4. Shore Hardness (ASTM D2240)

The resistance a material has to indentation. This measures the indentation hardness of substances such as thermoplastic elastomers, vulcanized (thermoset) rubber, elastomeric materials and some plastics.

5. Abrasion Resistance (ASTM D4060 - Taber Wear Index)

The rate of wear as calculated by measuring the loss in weight (in milligrams) per thousand cycles of abrasion. The lower the wear index, the better the abrasion resistance.

6. Low-Temperature Crack Bridging (ASTM C836 or ASTM C1305)

The ability of the material to maintain its integrity while bridging a crack in the substrate at low ambient temperatures when the polymeric materials are least likely to be flexible. Meeting this criterion allows the material to perform exceptionally at crack-bridging, a critical factor with construction-based waterproofing.

A waterproofing system should be evaluated on the basis of the results of this set of tests and should not be selected based on a single performance value. Importantly, the highest possible test value does not always translate into installed performance. Therefore the system should be evaluated in total to determine the likelihood of achieving the desired installed performance.

Notable Durability Differences Between Cold-Applied and Hot-Applied Waterproofing

Product Materials and Chemistry

Hot-applied liquid waterproofing systems consist of rubberized asphalt. Multiple layers must be applied to achieve durability, along with a reinforcement layer made of fleece and a protection board, which add complexity to the installation. Because of the additional skill set required for the installation of reinforcement and protection, there is a greater chance of errors occurring during the installation that could affect the watertight performance and durability of the product.

Cold-applied liquid waterproofing requires applying only one or two layers (after the primer) to achieve durable performance. Some of these systems do not require a reinforcement layer or protection course during construction.

Damage Resistance

Asphalt-type hot-applied liquid waterproofing is composed of large proportions of low and medium molecular weight components and consequently does not stand up well to equipment grease and solvents that may be dropped on the surface. Also, it can handle only limited loads or cycles of abrasion on its surface before showing wear or penetration.

Most cold-applied liquid waterproofing systems are reactive and made to form a high molecular weight or cross-linking polymer. This results in good resistance to wear and tear, the hydrocarbons, grease, or solvents that are often spilled on the jobsite. A properly selected cold-applied liquid system can handle construction or ongoing activity, including mishaps such as equipment and tools dropping on the surface. In a worst case scenario, an impact may break the concrete deck underneath the membrane and the waterproofing must have crack bridging capability to maintain its integrity.

Reactive cold-applied liquid waterproofing is often designed with the ability to handle “point loads,” which can be caused by a heavy piece of equipment with a narrow leg at the bottom or similar point load situations. Even in those instances, the membrane will not show a dent or penetration.

Overall, cold-applied waterproofing can handle greater loads and a higher number of cycles of abrasion than hot-applied.

Low Temperature Crack-Bridging

Crack-bridging is a critical feature of liquid waterproofing materials due to the natural dynamic movement of buildings and structures that understandably creates cracks. In climates with temperature changes from season to season, these cracks can shift, open and close. This back-and-forth movement of cracks as temperatures change creates many fatigue cycles for the waterproofing membrane.

Waterproofing materials need to withstand these various temperatures, and low temperatures in particular, so that when there is a crack in the substrate (typically concrete), the waterproofing membrane stays in its original condition. There will be no fine-line cracks or breaks in the membrane and it will remain monolithic, protecting the structure underneath by preventing water from getting through and damaging the structure.

Materials can become rigid—and some even brittle—when the temperature drops, rendering them unable to maintain their original condition under stress or repetitive movement. That is why, when choosing a waterproofing system, the material’s temperature-related properties and overall chemistry should be given serious consideration.

Hot-applied liquid waterproofing requires continuous maintenance to ensure the membrane’s protection of the surface below. With respect to durability, enduring fatigue cycles of building movement or maintaining integrity over time, especially in cold temperatures, is a challenge for hot-applied liquid waterproofing.

The elastomeric qualities inherent in cold-applied liquid waterproofing membranes mean that they easily withstand building movements and fatigue cycles, maintaining their integrity over a long period of time and requiring no ongoing maintenance. Cold-applied liquid waterproofing can also handle more extreme temperatures, down to -15-degrees Fahrenheit.

Application Durability

When applying hot rubberized asphalt at high temperatures, air will try to escape and moisture will try to evaporate through any defects in the primer, which can cause a good deal of blistering or pinholes.

Applying cold liquid greatly reduces the chance of evaporation of moisture and water trapped in concrete as well as expansion of trapped air in the concrete when compared to hot liquid application. With cold-applied waterproofing, it’s possible to build a continuous membrane for waterproofing integrity.

Conclusion: Which Type of Waterproofing is More Durable?

A waterproofing product is considered durable not only when it meets the six critical performance requirements, but also demonstrates the ability to handle jobsite conditions and maintain long-term performance in the service condition. In other words, it installs easily with minimal defects and is physically tough and chemically inert enough to handle the construction site abuse and long-term aging (such as from water or repetitive movement) to maintain its waterproofing integrity. Since reactive cold-applied liquid waterproofing products have the flexibility to be uniquely formulated to a specific purpose, a well-designed cold-applied liquid waterproofing product can meet all the requirements to provide the long-term performance needed. With such a product, builders and architects can trust they have a superior and efficient waterproofing system that will provide a seamless, robust and monolithic membrane that is more durable and longer-lasting, and will effectively and reliably seal and protect surfaces and structures from water penetration.