Sometimes a couch will look perfectly normal, or only slightly saggy, but when you sit down it sucks you in. Sagging upholstery is usually a result of broken springs inside of a couch or chair. You can temporarily boost up the seat by sticking a big board under the cushions, but it will not be very comfortable and can even cause more damage to the furniture. To repair sagging upholstery without causing more damage to your furniture, follow the step-by-step directions below.
Turn the sofa or chair upside down, and use the staple/tack puller to remove the cloth bottom cover. This will give you a clear view of the underside of the springs. Locate the broken spring or springs.
Using the staple/tack puller, remove the tacks holding the zigzag spring clips on both ends of the damaged spring. The spring will lift out when the clips are gone.
Fasten one end of the zigzag spring in the clip, making sure the clip wraps around the length of the flat end of the zigzag. One edge of the clip will have tack holes and the other will have a partially open coiled edge to hold the spring. Using the pliers, pinch the coiled edge of the clip to hold the spring tightly. Do not hook the clip on the curved edges of the zigzag spring because it will not hold very long. Place a clip on each end of the spring.
Position one clip, either one, over the holes where the original clip was located in the furniture's frame. Insert a tack in each hole, and tap it with the tack hammer until it is halfway in. Make sure the clip is straight, and use the tack hammer to gently pound the tacks in the rest of the way.
Push the other end of the zigzag spring into the frame of the furniture. The spring should curve away from your hands and toward the cushion. Position the second clip over the original holes on the opposite side of the frame, and use the tack hammer to pound in the tacks.
Position a piece of upholstery twine six inches from each end of the zigzag spring, where it attaches to the frame. Slide the twine ends under the closest spring and tie the twine pieces tightly, because it will keep the springs from sliding apart.
Replace the cloth bottom cover and tack it back in place with tacks and the tack hammer. Turn the furniture back over.
Zigzag spring is normally sold in rolls containing far more spring than a do-it-yourself-er is likely to ever need. Visit an upholstery shop to purchase short sections of zigzag spring. Measure the original springs before ordering the new zigzag springs from an upholsterer, because the springs are made of hardened steel that require special cutters. Sofas, even though longer than a chair, will have similar innerspring needs because frames are normally divided into cushion-wide sections.
Wear eye protection and gloves when doing upholstery work to protect yourself from sharp rusty items, tools, and springs.