The major portion of the raw edge (and adjacent areas) of the pouring spout of a plastic coated gable-top container is wet prior to heat sealing of the gable top and then the gable top is heat sealed to effect a liquidtight container closure. The wetting material, all or most of which should be a volatile liquid, coats the raw edge and penetrates the fibers of the coated stock. A wetting agent and/or a thickening agent is used to achieve wetting and to provide a coating of the wetting material on the raw edge and adjacent areas. The heat sealing step is performed promptly to avoid substantial loss of wetting material from the raw edge. The apparatus contacts the raw edge with a liquid-carrying member, e.g., a suitable sponge, which transfers the wetting material to the raw edge without dripping of wetting material into the container.