Polyurethane liquid membranes cure into a rubber-like, highly elastic film that can stretch and recover as the substrate beneath it moves. That flexibility is the entire reason they're specified: roofs, balconies, and terraces in a climate like Rwanda's go through daily heating and cooling cycles that open and close hairline cracks in the concrete underneath, and a rigid coating will eventually crack along with it. A polyurethane membrane bridges those movements instead of fighting them.

Application is straightforward for a trained applicator — roller, brush, or spray — and because it's a true liquid, it forms a seamless membrane that follows every upstand, drain outlet, and pipe penetration without the cutting and patching a sheet membrane would need. It also bonds well to a wide range of substrates, including old bituminous or tiled surfaces in some formulations, which is useful on refurbishment work.

The trade-off is cost and surface preparation. Polyurethane systems sit at the higher end of the price range compared with cementitious or bituminous coatings, and they demand a genuinely dry, clean substrate to cure properly — moisture trapped underneath can cause blistering. For a client weighing budget against the movement-heavy realities of an exposed rooftop, the extra spend on a polyurethane system is usually justified by the years of crack-free service it buys.