Upholstery and Interior Fittings
This domain tests frame construction, suspension, filling specification, fabric calculation and the fittings that make furniture work. Numerical questions usually involve foam volume or fabric quantity with pattern repeat.
Frames and suspension
- Frames in kiln-dried hardwood, usually beech, jointed with mortise and tenon, dowels or corner blocks glued and screwed.
- Webbing: jute or rubber, interwoven at right angles, tensioned so it deflects about 10–15%, stapled with three or four staples per end.
- Springs: coil springs tied eight-way, serpentine (S-shaped) springs clipped to the frame, pocketed coils for premium seating. Hessian over springs, then filling.
Fillings
- Polyurethane foam density: seats 30–35 kg/m3, backs 22–25 kg/m3, scatter cushions 20–25 kg/m3. Density controls durability; hardness (ILD) controls feel - they are different properties.
- Dacron wrap softens the feel; coir and horsehair are traditional, breathable fillings.
Covering
- Calico underlay, then top fabric. Seam allowance typically 15 mm; piping uses a 5 mm cord.
- Pattern repeat and railroading matter: velvet has a nap and must be cut in one direction; checks need matching at seams.
- Abrasion resistance: domestic upholstery usually 20,000 Martindale rubs, contract 40,000 or more.
- Staple in a straight line 10–15 mm from the edge, pulling fabric evenly, working from the centre outwards.
Fittings
- 35 mm cup hinges with overlay or inset mounting, 165° hinges for corner access; drawer runners side-mounted or undermount with soft close; shelf supports; sliding door gear.
- Fixings into panel edges: confirmat screws, cam and dowel, or dowels with glue.
Worked example
A seat cushion is 550 × 550 × 120 mm and uses 35 kg/m3 foam. Volume = 0.55 × 0.55 × 0.12 = 0.0363 m3, so mass = 0.0363 × 35 = 1.27 kg of foam per cushion.
Now four cushions, each cut at 650 × 650 mm, from 1400 mm wide fabric with a 320 mm straight-match repeat. The 650 mm cut rounds up to 960 mm (three repeats). Two 650 mm panels fit across the 1400 mm width, so four cushions need two rows: 2 × 960 = 1.92 m. Add 10% for matching and waste: order 2.2 m, not 4 m. Always check whether the fabric has an up direction before nesting two across.
Traps that cost marks
Ignoring pattern repeat and nap; underspecified foam density; over-stretched or slack webbing; staples not sunk; forgetting seam allowance; cutting two across when the pattern has a direction.
Show the arithmetic: volume × density for foam, cuts × repeat for fabric.