The provided context is not relevant to the question of how to fix a broken zipper and contains no instructional information. Therefore, this answer is based on general knowledge of textile and upholstery repair.
The methodology for repairing a broken zipper on a sofa cushion is contingent upon the specific nature of the malfunction. A thorough diagnosis of the issue is the necessary preliminary step toward an effective solution. Common points of failure include a disengaged slider, teeth that fail to interlock, a physically broken slider mechanism, a missing zipper stop, or significant damage to the zipper teeth or tape.
For minor issues, such as a slider that has come off one track or teeth that will not mesh, the repair can often be accomplished with simple tools. If the teeth are not interlocking, the slider may have become widened over time. A pair of pliers can be used to gently and incrementally squeeze the top and bottom plates of the slider together, which can restore the necessary tension to engage the teeth properly. If the slider has come completely off one or both tracks, it is often necessary to remove the metal stop at the base of the zipper, carefully re-feed both sides of the zipper teeth into the slider, and then use pliers to crimp the original stop back in place or create a new one by sewing a thick bar tack with a needle and thread.
In cases where the slider itself is fractured or the pull tab has broken off, the slider must be replaced. Zipper repair kits are widely available for this purpose. The process involves removing the old zipper stop, sliding the damaged slider off, and replacing it with a new one of the appropriate size and type before reattaching the stop. If the zipper teeth themselves are broken or torn from the fabric tape, a spot repair is generally not a durable solution. The most effective course of action for such extensive damage is a complete replacement of the zipper assembly. This requires using a seam ripper to carefully remove the old zipper from the cushion cover, followed by sewing in a new zipper of the same length, either by hand or with a sewing machine equipped with a zipper foot.
