Elongation At Break: A Misunderstood Metric In Concrete Waterproofing

The topic of elongation is often the center of attention when it comes to waterproofing works. In fact, it’s rare to attend a meeting, participate in a discussion or present on waterproofing without elongation being the primary focus. This is why we felt the need to highlight the importance of evaluating all relevant factors before determining the suitability of a product for a specific project. Elongation, or a product’s ability to stretch without breaking, is just one aspect to consider when selecting an appropriate waterproofing membrane for a concrete surface. Also, In our years of experience as Waterproofing Applicators, the property of elongation may not be as important as commonly believed in this context.

Let us dive a bit deeper to understand how the elongation strength of a membrane is recorded.
Elongation can be determined by International test standards ISO 37-2005 / ASTM D-638. This test takes a free film sample of the membrane to be tested and cuts it into a predetermined shape. The sample is then stretched until it snaps and the elongation and force required to stretch it to breaking point is recorded.

However, It has been argued that the elongation capability of a membrane is only available when it is in a free film state and not when it is securely stuck to the concrete substrate.
For example, imagine a rubber band. The rubber band has a certain amount of stretch or elongation before it snaps. However, if the rubber band is stuck to a surface and cannot move, it will not be able to stretch even if it is pulled. Similarly, once the elastomeric lining is securely adhered to the concrete substrate, it cannot elongate and has limited surface area to do so in case of a crack in the concrete.

Factors such as the thickness of the lining, the tensile strength, and the level of adhesion between the lining and the concrete have a greater influence on the product’s ability to handle cracks & maintain its integrity. In this regards, a more relevant test to consider is Crack bridging properties – DIN EN 1062-7 Procedure C.2.

Conclusion: The elongation properties are relevant in areas that experience differential movement such as expansion joints, wall and floor junctions, and junctions between concrete and steel fittings.
However, the correct application and pre-treatment techniques are even more important in determining the effectiveness of the product rather than its stretching capabilities. Some waterproofing membranes may have higher elongation, but if they are not applied correctly, they can still fail to perform well.

It is rare for a substrate to fail to the extent that a waterproofing membrane with 500% elongation would be necessary. In the unlikely event of such calamitous failure, there would likely be more pressing structural engineering concerns to address before the waterproofing.

In addition, the marketing of elongation as a key differentiator has led to an over-hyping of its importance, with manufacturers promoting products with high elongation percentages as a way to stand out in a crowded market. This has resulted in many contractors and engineers focusing too much on elongation, without fully understanding its true impact on the performance of waterproofing materials.

“Like a sturdy ship on stormy seas, elongation is an essential aspect of waterproofing membranes, but it is the craftsmanship of the captain and the soundness of the vessel that ultimately determine safe passage.”