Ask any engineer how waterproofing usually fails, and they'll give you one word: Joints. Water is the most persistent "invader" in nature. If there's even a one-millimetre hole in the junction between two materials, it will find it and get through.
Polyurethane liquid membrane systems were created to eliminate joints entirely. They are thick liquids (like very dense paint) spread on the roof with a roller, brush or spray. When they contact atmospheric moisture, a chemical reaction (polymerisation) begins. Within hours the liquid becomes a unified, hyper-elastic membrane. You're essentially turning your roof into a "pool" of solid rubber, without a single seam (Seamless)!
Why are more and more owners and engineers turning to this solution?
Buildings "breathe" and move. In summer they expand, in winter they contract. A quality polyurethane membrane has an elongation reaching 400% to 600%. You can literally stretch it like an elastic band and it won't tear. It therefore perfectly bridges the micro-cracks that form in concrete.
If your roof is full of solar-heater bases, aerials, cables and ventilation pipes, cutting and bonding bitumen membrane around them is a nightmare. The polyurethane coating is brushed around the pipe and "hugs" it airtight !
No fire, blowtorches or heavy machinery needed. With a good roller, careful cleaning and following the instructions, a homeowner can waterproof a small roof with professional results.
The success of polyurethane depends entirely on preparation. If you spread it over dust, it will peel off within a year.
The surface is pressure-washed and must be completely dry. Then the special polyurethane or epoxy primer is applied. It acts as "double-sided tape" that bonds to the concrete and waits for the polyurethane to "hook" onto it.
We apply the first "coat" of polyurethane. Important: At cracks, corners and junctions (e.g. where the wall meets the floor), we embed a strip of polyester fabric (geotextile) into the wet material. This acts like reinforcement in concrete, giving enormous mechanical strength to weak points.
After the first coat dries (usually 12-24 hours), we apply the second coat "cross-wise".
Basic (aromatic) polyurethanes yellow and "chalk" after years in the sun. For 20-year protection, professionals apply a final coat of Aliphatic Polyurethane . It's a varnish impervious to UV radiation that keeps the white colour gleaming permanently!
Our roof is full of pipes and solar heaters, so we rule out bitumen membrane. We buy polyurethane liquid coating.
We sweep the roof casually (dirt remains). No primer. We empty the can and roll it out, trying to save on material. Six months later the polyurethane peels off the floor like tape, because it bonded to the dust, not the concrete!
We pressure-wash and leave 3 days to dry completely. We apply a water-based polyurethane primer. We lay polyester reinforcement fabric at every corner around the parapets. We apply 2 thick coats of polyurethane (consuming 1.5 to 2 kg per m²). Finally we apply the aliphatic topcoat. The result? A gleaming, brilliant-white "basin" of rubber, without a single seam, that also reduces the home's temperature in summer!
The Final Conclusion: Polyurethane liquid coatings are the future of easy, fast and seamless waterproofing. Ideal for roofs with obstacles and accessible to diligent homeowners. However, they demand religious devotion to surface cleanliness and strict adherence to drying times.
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