The consumer usually never sees the construction features of an upholstered piece, but they are important. The overall quality of the materials and construction techniques used dictate the comfort level of an upholstered piece and its ability to satisfy the consumer over the long term. A basic upholstered piece is composed of a frame, springs, foam, decking, cushioning, padding, and a cover.
The frame gives structural support and determines the basic shape of any piece of upholstered furniture. If a frame is unstable, an upholstered piece will not be durable, no matter how fine or costly its design, padding, cushioning, or cover. Quality frames are generally made of solid wood, but plywood, engineered wood products, a variety of polymers and metals are also used.
Hardwood frames are usually constructed from kiln dried mixed hardwoods. White ash is a superior frame making wood. White oak, red oak, and American elm are good, and hard maple and birch are acceptable. Softwoods make poor frames.
Kiln drying reduces the moisture content of the lumber, a process which inhibits checking, splitting, and strengthens the finished product.
Engineered wood products may look not strong, but can be stronger than hardwood because the layers add to the strength. They are sometimes used at critical stress areas when maximum strength is needed.
Wooden frame joints are often double doweled, which means that round wooden pegs are fitted into holes in two adjacent frame sections and glued. Epoxy coated staples and gang nails are also commonly used. The gang nail is a metal plate with saw teeth, which immobilizes the joint when it is pressed into the wood with a hydraulic press. Major joints need the additional support of corner blocks, which should be glued and screwed into place.
Since lumber costs increase rapidly with increasing board thickness, some manufacturers may hold down frame coasts by skimping at the precise point where ample strength is most important. The engineering principal involved is that strength varies directly with rail width and with the cube of thickness. If we assume that a certain 1″x 1″ beam will sustain a load of 100 pounds, then a beam 1″ thick and 2″ wide will sustain 200 pounds. An old rule of thumb suggests that rails of 3″ or more in width should be 1-1/8th” thick, while rails less than 3″ wide should exceed 1-1/8″ thickness.
Springs or webbing are attached to the frame to give the seat a desired amount of elasticity. The most commonly used springs for furniture are coil springs, sinuous (sag-less) springs, and the Flexsteel ribcage spring system.
Upholstery with coil springs originated in France during the reign of Louis XV, replacing the method of stuffing hair or feathers over webbed frame covers. Coil spring upholstery did not however come into widespread use until the mid-1800’s when innovations such as the spring edge and springs in upholstered backs were popularized.
The bottoms of coil springs are normally clipped to the webbing base on which they sit. These springs are then compressed and tied with twine to the frame and each other. Eight-way hand tie (ties with eight knots) has been the industry standard and is a retail and consumer buzz word. Springs are tied to give them an initial tension sufficient to ensure an effect of order and neatness. They are also tied to hold them in the perpendicular position essential to proper spring action and to prevent shifting of the top of one spring in relation to the others. Tied springs also help to distribute the weight rather than placing it all on one or few springs and it bridges the open spaces inside of and around the top coils to provide support for filling materials.
Coil spring construction produces a firm, uniform seat, however, other methods which combine different kinds of springs, only webbing, flexible fabric, or soft cushioning materials and foams can produce high quality upholstered products.
A common spring construction method, which produces a comfortable soft upholstered front edge, is a spring edge. With the spring edge, the tops of the springs are positioned well above the top rail of the frame to form a firm but flexible floating edge.
Sagless springs, webbing, flexible foundation fabric, a drop-in unit, a simple wood platform of other types of spring units can be used instead of the more labor intensive hand tied coil spring constructions. Sagless springs are attached to the frame with steel clips or tacks. Helical springs are then used to connect them. The degree of comfort derived from this method depends on the resiliency of the spring.
Webbing, which traditionally consisted of linen or jute band assembly, has now been largely replaced by synthetic webbing materials. Webbing and solid panels can also be used as the deck for top cushions instead of springs.
Another type of spring system is the Flexsteel blue ribcage spring system. In the late 1800íthe founders of Flexsteel purchased Swiss watch spring steel to create a new spring system. This steel is used in the spring movement of watches and clocks because of its continuous flexibility and strength. The steel gets stronger the more times it is flexed. This allows the Flexsteel ribcage spring system to give everlasting comfort, durability, and reliability for as long as you own your sofa.
In conventional (coil spring) constructions, layers of padding are added on top of the springs or webbing to complete the deck (the area under the seat cushions). In quality upholstery applications, the deck should be well padded, with no bumps or lumps. The padding should extend to the front edge of the deck, completely covering the spring edge or frame.
Loose or attached cushions sit on top of the deck. The majority of cushions are made up of polyurethane foam. A ìrshal unit,îade up of coil springs, which are sewn in pockets and then attached. Down or synthetic down-like materials may be used instead of foam in some upholstery applications.
Polyurethane foam seat cushions which contain high-density foam (2.0 pounds per cubic foot polymer density or greater) are desirable. They offer better support and durability than lower density foams. Back cushions do not need foam that is as dense, but shredded foam which is cheaper to use, may eventually shift, compact and settle, getting lumpy and uneven looking.
Cushions are normally wrapped or capped (crowned) with polyester, low-density foam or other soft material for added surface plushness. This wrapping should give the cushion a softly rounded look. It also helps prevent the fabric from rubbing against the dense foam core and fills cushion corners.
Q: What is pilling, and what are the effects regarding my fabric?
A: Pilling is characteristic of many upholstered fabrics and results from excess fiber coming off the surface of the material. This release of excess fiber results in small balls or “pills” forming on the surface of the material. This condition is not warranted by the fabric mills because it is not a defect. It is simply excess material being released. This is similar to the fuzzing experienced with new carpet or the pilling of a new sweater. The concern of some consumers has been that the fabric is disintegrating and will ultimately leave a bald area on the cover. That is not the case. As with carpets and sweaters, the pilling will persist until the excess fiber is gone, and then it will cease. The best treatment while this is happening is to simply shave the fabric with a battery operated furniture or sweater shaver to remove the pills and restore the look of the cover surface. This may need to be done 3-4 times, but the pilling on the surface will begin to diminish and ultimately stop.