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Elastic membranes on flat roofs: cracks, movement and continuity

How an elastic coating copes with cracks and movement in the substrate, why thickness matters and what to check on the roof.

By Equipo Humix Paint · Reviewed on

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If you're looking for the practical steps and how to calculate the product, read How to waterproof a flat roof step by step. Here we explain how an elastic membrane works on a roof.

First understand where the water gets in

On a flat or low-pitched roof, the waterproofing has to stop rainwater reaching vulnerable layers of the building. Entry points can be concentrated at drains, junctions with parapets, service penetrations or small cracks. Before applying a new coating, check drainage, the stability of the substrate and the condition of the construction details.

Elasticity and continuity of the film

An elastic coating forms a film that has to remain continuous across the surface and its junctions. How it responds depends on the formulation, the applied thickness and the movement of the base. A film that's too thin or interrupted can leave weak points; that's why the rates and coats specified by the manufacturer aren't decorative details but part of the installation.

Waterproofing isn't the same as studying solar reflectance

For roofs, solar reflectance and thermal emittance are also studied: parameters that describe how the surface interacts with radiation. ENERGY STAR explains these concepts for reflective roofs. However, using a light colour or adding microspheres isn't enough to claim energy savings or a specific temperature: those figures require testing and comparison conditions.

What Cool Roof Therm states

Humix Paint's documentation describes Cool Roof Therm as an elastic, liquid-applied waterproofing coating, water-based, with CaCO₃® Technology (graphene) and glass microspheres. Its data sheet states it's waterproof against rainwater, works its way into small cracks to form a continuous elastic layer, and has high elasticity and tensile strength. It's designed for horizontal outdoor surfaces such as flat roofs, terraces, domes, vaults and overhangs.

Application and quality control

The product comes ready to use and should be applied in as many coats as needed to reach the stated consumption of 1–1.5 kg/m². The data sheet states it can be walked on once fully cured. Before application, check that the substrate conditions are compatible with the system, deal with the critical details and follow the technical instructions. On roofs with structural damage or complex active leaks, a professional assessment is needed.

Conclusion

How a waterproofing system performs depends on the product, the substrate, the details and correct application. A good diagnosis of the roof is as important as choosing the coating.

Technical and scientific sources

Guía escrita y revisada por el Equipo Humix Paint con los datos de las fichas técnicas de cada producto. La pintura actúa en la superficie: si el agua sube del suelo o entra de fuera, primero se trata la causa.

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