Hotel Lobby Sofas Failing at Six Months: Foam, Frame and Specification

Foam. 24 kg/m3 cut polyether is domestic-grade. For severe contract use, the core should be 35-40 kg/m3 high-resilience moulded foam with a 25% IFD around 130-160 N and a support factor (65% IFD divided by 25% IFD) of at least 2.3. The support factor is the number that matters for a 130 kg user: it describes how quickly the foam stiffens as it compresses. Low-density cut foam has a low support factor, so it bottoms out early, the load goes straight into the suspension, and the foam takes a permanent set - which is the 25-30 mm flattening measured.

Thickness and crown. 120 mm is adequate in principle, but a flat-cut block with no crown and only 100 g wadding gives no shape recovery and no tension in the cover. The 'drum' at the front edge is the foam crushing at the point where the thigh loads it and the cover has nothing to pull against.

Suspension. Elastic webbing at 60 mm spacing over a 550 mm deep seat gives about nine straps, each carrying the share of the load with no interlinking. Under a 130 kg point load the straps extend, the foam follows them down, and the seat takes a set. Contract work normally uses serpentine springs clipped to a rigid frame and tied, or a rubber-webbing grid at 50 mm or less with a woven platform, and the foam supported on a stiff deck.

The staple margin. Staples 20 mm from the rail edge will pull out under that load, which is exactly what makes the covers slack and creased. The margin should be 30-40 mm into sound, dry timber, with the webbing folded back and double-stapled.

Conclusion. The sofa is not defective; it is a domestic specification in a contract environment. No repair will fix that - the core and suspension have to be replaced, not re-tensioned.

Diagnosis. A butt joint held by two screws and a nailed plywood block carries almost no bending moment. The screws act as dowels in end grain - the weakest possible purchase - and the block, glued with PVA to end grain, has little strength from the start. The crack in the rear corner block and the creak at the arm/leg joint are the same mechanism: repeated racking under shifting body weight works the joint open, the nails loosen, and the creak is movement at a fastener that is no longer clamped.

Moisture content. Beech at 12% MC is too wet for a heated interior. In a lobby at 20-22 C the equilibrium will settle around 6-8%, so the frame shrinks after assembly. Joints that were tight at 12% open, and the 12 mm ply corner block - which shrinks across its thickness far more than the beech rails - splits or shears its glue line. Specify 8-10% MC at assembly, measured on a sample from each batch, and condition the cut components in the assembly area before gluing.

Re-specified corner.

• Mortise-and-tenon, haunch or through as the design allows, with tenon width about one third of the rail width and a minimum 25 mm depth; or, if the rail section is too small, three dowels of 10 mm at 30 mm centres with the outer dowels staggered.
• Corner blocks are a reinforcement, not the joint: glue and screw them, do not nail them, and use a block that will not shrink differentially - solid beech or a hardwood block rather than 12 mm ply.
• Adhesive: a D3 or D4 PVA for interior and any humid risk, or a two-pack PU where gap filling and moisture resistance are needed. PVA alone on end grain is not enough, and the wood must be cramped to a genuine glue line.
• Add a corner gusset or a screwed steel angle on the rear corners if the frame geometry cannot take a proper tenon.

Verification. Build one prototype to the revised specification and have it tested to EN 16139 using the EN 1728 test methods, with stability to EN 1022, before touching the remaining eleven.

What can be salvaged. The frames and covers are recoverable in principle, but the covers have taken a set over failed cores and will not fit properly over new, fuller cushions. Expect to replace cores and covers on all twelve, and to repair the frames.

Remediation sequence.

1. Strip each sofa: covers off, webbing out, corner blocks removed.
2. Repair frames: open the cracked corners, clean out old adhesive, reglue with a proper tenon or dowel plus glued-and-screwed solid corner blocks, and check every other joint while it is accessible. Clamp and leave for a full cure, not overnight-and-hope.
3. Replace suspension: serpentine springs on a clipped and tied frame, or a tighter webbing grid with a stiff platform under the foam.
4. New cores: 35-40 kg/m3 HR foam, 120-130 mm with a crown, wrapped and bonded to a polyester or fibre pad; add a slip cloth.
5. Re-cover to the same pattern with adequate seam allowance and a lining, then inspect under raking light.

Programme and disruption. Allow about 2-3 working days per sofa with two upholsterers, so roughly 5-6 weeks if done in the workshop - less if done on site in a vacant floor with the sofas rotated two at a time. On-site work avoids removal and transport damage and keeps the lobby in service.

Commercial judgement. The specification was domestic and the client's brief was contract; that is the workshop's error and the remediation should be borne without argument - it is cheaper than a rejection claim plus the reputational cost with a hotel group. But it should be settled as a negotiated package, not an open-ended obligation: a written agreement covering scope, a defined completion date, and a credit in place of further liability. Then build the next batch properly and use this job as the reference for the specification sheet - foam grade, MC, joint detail and test standard on one page, attached to every quote.