A system for stopping in an opening a flow of a fluid, wherein the system comprises: a kneadable silicon based polymer for fitting in and/or onto the opening so as to block any flow of the fluid through the opening, wherein the silicon based polymer comprises fillers so that the density of the silicon based polymer is higher as compared to the density of the silicon based polymer that does not comprise these fillers, and a silicon based sealant for applying against a dried form of the silicon based polymer, wherein the silicon based sealant is vulcanizable under exposure to humidity.