In the method for sealing of replacement windows, a sealing tape with a first layer of flexible foam and a second layer of stiff material, which are bonded to each other, is used. The sealing tape is inserted with the second layer facing forward into a channel-shaped recess in the masonry, which is bounded by a bottom and two side walls and comprises an open access section, wherein the first layer of the sealing tape is at least partially compressed when in the inserted state. The second layer of the sealing tape is clamped against the side walls of the recess at a predetermined distance from the open access section. After the window frame has been placed opposite the open access section of the recess, the first layer of the sealing tape expands until it rests against the window frame.