The elongation properties of membranes play a key role in the durability and performance of buildings, and especially foundations. These properties allow the membranes to adapt to the constraints and movements of a building, thus avoiding major issues such as cracks or infiltration.
A poor understanding of these properties can result in an inappropriate choice of membrane, compromising the overall performance of a project. In order to help professionals make an informed choice, this article explains what elongation is, what the different types of elongation are and how properties vary from one technology to another.
What Are the Elongation Properties of a Membrane?
Elongation is the ability of a material to deform under tensile stress. Elongation is usually expressed in percentage (%). Basically, two points are plotted and the distance between them is referred to as the Initial Length. After applying a tensile stress, the distance between these two points is measured again, corresponding to the Final Length. For all such types of measurement, the elongation is calculated using a simple equation:
Although this technical definition applies almost universally to any elongation measurement, not all elongation measurements are the same. In the case of a waterproofing membrane, we often speak of a composite material or an assembly, i.e. different components, each making their own contribution to the performance of the product.
When it comes to evaluating these performances, it is possible to use different standardized test methods that provide a precise elongation measurement of one or the other of product elongation properties. Although a higher elongation capacity is always advantageous for the building, each test highlights different properties which cannot be compared directly. For example, evaluating the elasticity of a binder by elongation at break according to ASTM D412 does not provide the same information as a measurement of the elongation at peak load of a membrane with reinforcement according to ASTM D5147.
The Importance of Membrane Elongation Properties
The elongation properties of a waterproofing membrane are crucial in construction for several reasons, not least to guarantee the performance and durability of buildings.
The following points demonstrate the importance of these properties.
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Adaptability to building movements: Buildings may move slightly due to temperature variations (freeze/thaw cycles), wind loads, ground motion or depending on the area or region. A waterproofing membrane with good elongation capacity can accommodate these movements to some extent without tearing, thus ensuring continuous protection against moisture.
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Crack prevention: Even if surfaces are prepared according to recommendations, they can be irregular or involve joints between different materials. Thanks to their elongation performance, waterproofing membranes can better cover these areas without cracking, which is essential to maintain the waterproofing integrity.
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Increased durability: Membranes that can stretch without breaking tend to have a longer service life. They are more resistant to mechanical stress and harsh environmental conditions, thus reducing maintenance and replacement needs.
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Examples include:
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Construction on unstable ground.
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Buildings subject to extreme temperatures or freeze/thaw cycles.
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Why Are Elongation Properties Not the Same in All Membranes?
Not all membranes have the same elongation performance. This is due to the type of technology (liquid vs. bituminous) and the different requirements and the conditions to which they are exposed in their specific applications. Here are some main factors that impact the type of elongation properties sought.
Type of structure:
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Roofs – Membranes used for roofing often have to withstand significant thermal movements and wind loads.
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Foundations (pre-applied or conventional) – Foundation membranes must withstand ground motion and groundwater pressure.
Environmental conditions: In regions with extreme climates and significant temperature variations, membranes must have greater elasticity to avoid cracking due to expansion and contraction. The same applies in areas where the ground is unstable.
Type of materials: The materials used and their manufacturing methods have an impact on the performance of the different technologies.
Quality of the substrate: Membranes applied to irregular surfaces or joints between different materials must be more flexible to ensure complete coverage without cracks. However, on smooth, even surfaces, membranes with less elasticity may be sufficient.
These variations illustrate why it’s important to choose the right waterproofing membrane according to the specific needs of each project.
The Different Types of Elongation
The elongation of a membrane can be measured at various points on its stress-strain curve:
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Elongation at maximum force
When a membrane is subjected to tensile stress, it deforms by elongation. The final length used in the calculation is the one measured when the tensile strength is at its maximum. In the case of elastomeric membranes, the elongation at maximum force is often used to indicate the elongation the membrane can undergo before the first breakage of its components. This breakage usually highlights the properties of the reinforcement and the stronger and more rigid membrane components, and is therefore generally to be tested in conjunction with the maximum load a product can withstand. -
Elongation at break
Depending on the testing methods used, the break point can have different meanings. For some methods, the break point is determined at the moment of complete membrane failure, while other ones determine the break point when the reinforcement ruptures (in the case where reinforcement is one of the membrane components). Elongation at break is useful for understanding how much deformation a membrane can undergo before potentially leading to a leak. -
Ultimate elongation
Many evaluation methods use ultimate elongation interchangeably with elongation at break. For some others, however, ultimate elongation is defined as the force on the stress/strain curve when it reaches 5% of its maximum value. In these cases, the ultimate elongation is similar to the elongation at break of the binder. -
Elongation at break of the binder
If the membrane is reinforced, the breaking of the reinforcement does not necessarily cause a water leak, as long as the binder remains intact. The elongation at break of the binder can give an indication of the total deformation that the membrane can undergo before water can no longer be retained. With certain methods allowing extreme elongations, the deformation of a binder is evaluated up to its very limit, even going beyond the binder’s waterproofing capacity to instead highlight the limits of its elastomeric behaviour. This indirectly allows the fatigue resistance to cyclic phenomena, such as the contraction and expansion of a building to be evaluated.
How Do Elongation Properties Vary in Relation to Membrane Technology?
| Types of elongation | Method used | Heat-welded sheet membranes | Sheet membranes | Liquid membranes |
|---|---|---|---|---|
| Products | COLPHENE FLAM 180 | COLPHENE 3000 | COLPHENE LM BARR | |
| Elongation at break | ASTM D5147 | 60–65% | 25–40% | |
| Elongation at break of the binder | ASTM D5147 | > 1,000% | ||
| Elongation at break | ASTM D412 | 55–88% | 378 % |
Elongation at break, measured according to ASTM D5147, evaluates the tensile strain capacity of a reinforcement, such as a polyester reinforcement or a structural film. This method mainly reflects the elongation capacity of the reinforcement.
ASTM D412, on the other hand, is primarily designed to evaluate homogeneous products without reinforcement. This method is therefore often used to test liquid membranes without reinforcement or the binders of reinforced membranes. In some cases, ASTM D5147 can also be used to evaluate bituminous binders, as is the case for COLPHENE 3000.
As these examples show, data analysis requires careful interpretation. It is impossible to determine which membrane stands out solely based on the elongation values shown in the table. A complete evaluation must integrate other properties, as well as all environmental parameters.
Conclusion
The elongation properties of membranes are not a mere technical feature. They determine the performance and durability of a building by meeting specific mechanical and environmental constraints.
Understanding the different forms of elongation and their relevance to different types of membranes ensures that the most suitable solution is chosen for each project. Ultimately, the right choice of membrane not only ensures better protection, but also increased durability, thus reducing long-term maintenance costs.