Vinyl Sheet Flooring: Cushion vs Felt-Back, Seam Welding, Adhesive Types and Subfloor Requirements

Quick Answer: Vinyl sheet (PVC sheet flooring) comes in two main types: cushion-back (foamed PVC layer for comfort and sound insulation) and felt-back (fibreglass/felt stabiliser for dimensional stability). Both require a smooth, dry subfloor to ±3mm under 3m. Seams must be heat-welded in commercial environments and in wet areas. Adhesive type depends on the specific product: full-bond, perimeter bond, or loose-lay.

Summary

Vinyl sheet is the most cost-effective and most practical floor covering for kitchens, bathrooms, utility rooms and commercial areas. Its continuous surface is inherently waterproof when properly sealed at edges and seams — unlike LVT or tiles where grout joints can trap moisture.

The flooring industry distinction between cushion-back and felt-back is important: cushion-back vinyl uses a blown PVC foam layer for softness underfoot and is typically used in domestic settings; felt-back vinyl has a fibre reinforcement that makes it more dimensionally stable, better suited to full-bonded installations and commercial use.

The biggest installation errors with vinyl sheet are: tolerating subfloor imperfections (embossing shows through thin sheet within weeks), over-applying or under-applying adhesive, and failing to weld seams in wet areas (allowing water ingress under the sheet causing adhesive failure and mould).

Key Facts

• Embossing — Surface imperfections in the subfloor telegraph through vinyl sheet — particularly with thin gauges (2mm) and under heavy traffic. The BS 8203 tolerance of ±3mm under 3m is the acceptable limit; tighter tolerance required for thinner products.
• Sheet widths — Standard: 2m, 3m and 4m wide rolls. Plan room to minimise seams (or eliminate entirely with a single width).
• Cushion-back — Cannot be fully bonded (adhesive traps moisture under foam, causing foam breakdown). Use perimeter bond only.
• Felt-back — Can be full-bond, perimeter-bond, or loose-lay depending on product TDS. Full bond preferred in commercial.
• Adhesive coverage — Over-application of adhesive causes air bubbles and ridges as it cures. Follow coverage rates precisely.
• Heat-weld seams — Mandatory for vinyl in wet areas and most commercial specifications (Altro, Polyflor specify weld). Use 4mm welding cord matching sheet colour; weld with hot-air gun at 350–400°C.
• Drying time before walking — Typically 24–48 hours for adhesive to set. Earlier trafficking risks ridging.
• Subfloor moisture — Test to ≤75% RH or ≤0.5% CC moisture before laying. Even in bathrooms, the subfloor moisture affects adhesive integrity.
• Cuts at threshold — Use a threshold bar to protect the edge and prevent lifting. Choose threshold depth to match sheet thickness.
• Trowel notch size — Typically B1 (1mm square notch) for vinyl sheet. Not a V-notch. Check adhesive TDS.

Quick Reference Table

Detailed Guidance

Choosing Between Cushion-Back and Felt-Back

Use cushion-back when:

• Comfort underfoot is important (kitchen, living room)
• The floor will not be fully bonded (perimeter bond or free-lay)
• Budget is the primary concern (cushion-back is typically cheaper per m²)

Use felt-back when:

• Full adhesive bond is required (commercial, heavy contract use)
• Long runs need dimensional stability (felt-back shrinks less)
• Seam welding is mandatory (weld-ready products are almost all felt-back)
• The specification requires Altro, Polyflor or equivalent safety flooring

Subfloor Preparation

Vinyl sheet demands the most exacting subfloor of any floor covering — even a 1mm screw head shows as an embossed bump within months. Follow the same preparation steps as for LVT:

1. Cure existing subfloor — concrete must be minimum 28 days old; screed minimum 21 days.
2. Moisture test — Insitu hygrometer probes (72-hour soak) or calcium carbide test. Do not proceed if >75% RH.
3. Repair defects — Fill all holes, cracks, and indentations with featheredge filler compound. Grind down high spots.
4. Apply SLC — If subfloor varies by more than ±3mm under 3m, apply self-levelling compound.
5. Check flatness — 3m straightedge and 3mm feeler gauge. Check diagonally as well as square to walls.

For timber subfloors:

• Screw all boards at 150mm centres
• Apply 6mm ply overlay screwed at 100–150mm centres
• Fill screw heads and joint lines with flexible filler; sand flat when dry
• Check flatness again before laying

Adhesive Selection

Application:

1. Roll out sheet; mark cut lines; cut undersized (10mm from each wall initially).
2. Fold back half the sheet. Apply adhesive to floor with correct notch trowel (B1 for most vinyl sheet).
3. Allow adhesive to reach open time (tacky but not wet — varies: 5–30 minutes depending on product and temperature).
4. Lay sheet back into adhesive; press from centre outward with a roller (100kg minimum roller for full bond).
5. Repeat for second half.
6. Trim accurately to walls with a straight edge and trimming knife.

Seam Welding

Seam welding creates a completely waterproof and hygienic joint — essential in wet areas and specified in most commercial standards.

Cold weld (chemical fusion):

• Apply cold welding solution with applicator nozzle directly into the seam
• Creates chemical bond between sheet edges
• Faster than hot weld; not as permanent; not suitable for commercial wet areas

Hot weld (heat welding):

1. Allow adhesive to cure completely (minimum 24 hours after laying)
2. Cut a 4mm groove exactly along the seam joint using a seam-routing tool (V-groove router or U-groove router)
3. Cut welding cord to same length as seam plus 50mm extra
4. Set hot-air gun to 350–400°C
5. Feed welding cord through the gun nozzle into the groove; apply constant heat and pressure
6. Allow to cool completely (do not disturb)
7. Trim proud weld flush with sharp trimming knife at two passes: first when still slightly warm, then when completely cold

Edge Sealing and Finishing

Coved skirting (integral cove):

• Used in commercial, medical, and food preparation environments
• 50–75mm radius cove creates a seamless junction at floor/wall
• Formed with heat from a hot-air gun; secured with contact adhesive

Standard domestic finish:

• Trim sheet to leave 2–3mm gap at skirting
• Seal gap with matching silicone or acrylic sealant

Thresholds:

• Use Z-bar (step-down) or T-bar (level) threshold to protect edge against traffic and moisture ingress

Frequently Asked Questions

Can I lay new vinyl sheet over old?

Yes, if the old sheet is fully bonded, flat, and not contaminated. Remove any lifting or bubbled sections. Use a self-levelling compound over the join lines and any ridges. The combined thickness must still meet the manufacturer's maximum thickness over the subfloor. Do not lay over existing welded-seam sheet (the ridges will emboss through).

How do I prevent vinyl sheet from wrinkling?

Wrinkling is caused by: excessive moisture under the sheet, inadequate adhesive spread, not rolling the sheet after laying, or thermal expansion without adequate bonding at perimeter. Ensure: the subfloor is dry, use correct adhesive coverage, roll immediately after laying, and perimeter-bond within 300mm of all walls.

Can I lay vinyl sheet in conservatories?

Vinyl sheet is not recommended for conservatories with high temperature variation — repeated thermal cycling causes dimensional change, adhesive failure, and lifting. LVT or ceramic tiles are more stable. If vinyl sheet is specified, use a full-bond felt-back with a temperature-stable adhesive.

Regulations & Standards

• BS 8203:2017 — Code of practice for installation of resilient floor coverings

• COSHH Regulations 2002 — Adhesive fumes during application; provide ventilation

• Construction Products Regulation (CPR) — Sheet vinyl must carry CE marking with declared slip resistance

• BS EN ISO 10874:2012 — Resilient, textile and laminate floor coverings: classification

• Contract Flooring Association — Vinyl sheet installation guide

• Polyflor Technical Services

• Altro — Technical installation information

• F. Ball & Co — Adhesive selection guide

• subfloor preparation — Subfloor preparation fundamentals

• floor levelling — Self-levelling compound for smooth substrate

• lvt installation — LVT as an alternative to sheet vinyl

• wetroom construction — Sealing and waterproofing for wet rooms