A composition that includes at least one silane-functional polymer P and 20 to 60% by weight of aluminum hydroxide or magnesium hydroxide or mixture thereof, is disclosed. The composition has a viscosity of 500 to 20,000 mPa·s measured according to DIN 53018 at a temperature of 20° C. The composition is suitable as a liquid membrane and has very good flammability properties, i.e., it is difficult to ignite and is self-extinguishing.