Method for pressure watertight sealing of polymeric fresh concrete composite films in the field of joints, penetrations and/or connections by application of a liquid sealant based on alkoxysilane-functional polyether polymers, wherein the liquid sealant is applied in liquid state to the composite film, and is then caused to cure, wherein a liquid sealant based on silylated polyurethanes is used, comprising A) silylated polyurethanes which are prepared either by (i) reacting isocyanate prepolymers based on long-chain polyethers with aminosilanes of the general chemical structural formula wherein R represents an organic residue having 1 to 12 carbon atoms, n represents an integer of 1 to 4 and X, Y, Z represent identical or different organic residues provided that at least one of the residues has an alkoxy group having 1 to 4 carbon atoms, preferably a methoxy or ethoxy group or by (ii) reacting long-chain polyether polyols, preferably polyether diols, with isocyanatosilanes of the general structural formula wherein n, X, Y and Z have the above-mentioned meaning; B) at least one basic filler, such as precipitated or ground chalks, metal oxides, metal sulfates, metal silicates, metal hydroxides, metal carbonates and metal hydrogen carbonates; C) at least one aminosilane of the general formula wherein R" represents a hydrogen atom or an organic residue, preferably an aliphatic hydrocarbon residue having up to 20 carbon atoms, a trialkoxysilylpropyl group or an aminoethylene group and n, respectively X, Y, Z have the above-mentioned meaning, preferably including mixtures and/or condensation products of aminosilane compounds; D) optionally further auxiliaries. A) silylated polyurethanes which are prepared either by (i) reacting isocyanate prepolymers based on long-chain polyethers with aminosilanes of the general chemical structural formula wherein R represents an organic residue having 1 to 12 carbon atoms, n represents an integer of 1 to 4 and X, Y, Z represent identical or different organic residues provided that at least one of the residues has an alkoxy group having 1 to 4 carbon atoms, preferably a methoxy or ethoxy group or by (ii) reacting long-chain polyether polyols, preferably polyether diols, with isocyanatosilanes of the general structural formula wherein n, X, Y and Z have the above-mentioned meaning; (i) reacting isocyanate prepolymers based on long-chain polyethers with aminosilanes of the general chemical structural formula wherein R represents an organic residue having 1 to 12 carbon atoms, n represents an integer of 1 to 4 and X, Y, Z represent identical or different organic residues provided that at least one of the residues has an alkoxy group having 1 to 4 carbon atoms, preferably a methoxy or ethoxy group or by (ii) reacting long-chain polyether polyols, preferably polyether diols, with isocyanatosilanes of the general structural formula wherein n, X, Y and Z have the above-mentioned meaning; B) at least one basic filler, such as precipitated or ground chalks, metal oxides, metal sulfates, metal silicates, metal hydroxides, metal carbonates and metal hydrogen carbonates; C) at least one aminosilane of the general formula wherein R" represents a hydrogen atom or an organic residue, preferably an aliphatic hydrocarbon residue having up to 20 carbon atoms, a trialkoxysilylpropyl group or an aminoethylene group and n, respectively X, Y, Z have the above-mentioned meaning, preferably including mixtures and/or condensation products of aminosilane compounds; D) optionally further auxiliaries.