LVT and Vinyl Flooring Installation: Adhesive vs Floating, DPM Requirements and Moisture Testing

Quick Answer: LVT (Luxury Vinyl Tile/Plank) can be installed loose-lay, floating (click system), or fully adhered depending on the product. On concrete subfloors, moisture must be tested — RH ≤75% for most standard adhesive products, ≤80% for specialist formulations. A DPM (damp-proof membrane) is required on all concrete subfloors unless moisture testing confirms compliance. Fully adhered LVT is the most dimensionally stable and is preferred in high-traffic commercial and areas with underfloor heating.

Summary

LVT and vinyl plank flooring has become one of the most popular flooring choices in UK domestic and commercial fit-outs. The appeal is clear: waterproof, hard-wearing, available in convincing wood and stone effects, and quick to install compared to tile or hardwood. However, poor subfloor preparation — particularly uncontrolled moisture — is the main cause of failures, especially adhesive bond failures and plank curling.

There are three main installation methods: fully adhered (glue-down), floating click-system, and loose-lay. Each has different subfloor requirements, and the method choice affects performance in areas with underfloor heating, in wet rooms, and in heavy commercial traffic situations.

This guide covers all three methods, subfloor preparation and moisture testing, DPM requirements, and common failure modes.

Key Facts

• LVT types — Glue-down (full adhesive), floating click (Uniclic, Clic-It, etc.), loose-lay (gravity held), peel-and-stick (not recommended for commercial use)
• RH threshold for adhesive LVT — relative humidity of subfloor moisture ≤75% for most standard adhesives; some specialist moisture-tolerant adhesives rated to 85–90% RH
• BS 8203:2017 — code of practice for installation of resilient floor coverings; key reference standard
• Calcium carbide (carbide bomb) test — invasive; most accurate moisture measurement; result in % moisture equivalent (ME%)
• Hygrometer (in-situ probe) — preferred method per BS 8203; 72 hours minimum equilibration; result as % RH
• Acceptable screed RH — ≤75% for standard installation per BS 8203; allow 1mm depth to dry per day as rule of thumb (varies with heating and airflow)
• Levelling compound — subfloor flatness: 3mm in 1.8m per BS 8203; use flow-screed or polymeric levelling compound; do not use gypsum (anhydrite) compounds under vinyl without specialist sealer
• Acclimation — most LVT requires acclimatisation at room temperature (18–27°C) for 24–48 hours before installation; check manufacturer's specification
• UFH compatibility — most LVT rated to max 27°C floor surface; floating LVT generally not recommended with UFH; fully adhered (glue-down) preferred
• Minimum subfloor temperature — most installations: minimum 15°C subfloor and air temperature during and 48 hours after installation
• DPM for concrete — required unless verified dry; 1000-gauge polyethylene DPM or liquid-applied epoxy DPM

Quick Reference Table

Detailed Guidance

Subfloor Preparation

Concrete Subfloor (Most Common)

1. Moisture testing — in-situ hygrometer probe (preferred) or carbide bomb test. Leave hygrometer for minimum 72 hours, sealed with insulating tape. Record % RH.

   • ≤75% RH: standard adhesive LVT can be installed
   • 75–80% RH: use moisture-tolerant adhesive; re-test to confirm

   • 80% RH: DPM required before LVT; re-test after DPM installation

   • 90% RH: likely active moisture ingress; investigate source before proceeding

2. DPM options (where required):

   • Polyethylene sheet DPM — 1000-gauge (250 micron); laid before levelling compound; lapped 200mm at joints, taped; turned up at walls 50mm
   • Liquid epoxy DPM — applied directly to concrete; tolerates up to 98% RH; bonds directly to concrete; levelling compound applied on top; 2-coat system typical; faster than waiting for slab to dry
   • Note: anhydrite (calcium sulphate) screeds can be treated with liquid DPM but check compatibility with the levelling compound

3. Levelling and flatness:

   • Fill hollows, remove high spots
   • Apply suitable levelling compound; match product to subfloor type (concrete, existing ceramic, timber)
   • Allow full cure time before installation (check compound datasheet — typically 30–60 minutes to foot traffic, 24 hours for LVT)
   • For thick build-ups (>10mm), use a two-pass system or specialist deep-pour compound

Timber Subfloor

• Minimum 18mm structural grade plywood over joists; 12mm overboard if existing floor already 18mm+
• Check for movement — bounce test; any spring or flex will cause joint lines to crack in click LVT
• Fix loose floorboards or ply: screw at 200–300mm centres
• Flatness: 3mm in 1.8m (same as concrete)
• Moisture: timber should be ≤12% MC (MC% not RH); check with moisture meter
• Apply DPM on timber suspended floors only if recommended by LVT manufacturer for the specific product

Fully Adhered LVT Installation

1. Select adhesive — pressure-sensitive (dry-to-touch before laying), hard-set (weld bond), or moisture-tolerant type; check product compatibility with the specific LVT
2. Apply adhesive with notched trowel (trowel notch size specified by adhesive manufacturer; typically V-notch 1.5 × 1.5 × 1.5mm for 2mm LVT)
3. Flash off time — wait for adhesive to reach specified tack (check with finger — should string slightly but not transfer fully); critical for bond quality
4. Lay planks/tiles starting from a chalk line central to the room
5. Roll with 68kg steel roller within 30 minutes of laying; ensures full bond
6. Seam sealing (for sheet vinyl) — seam sealer applied with special applicator bottle; creates monolithic waterproof surface

Click/Floating LVT

• No adhesive; planks click together via tongue-and-groove or Uniclic system
• Expansion gap: minimum 8–10mm at all walls and fixed objects; covers with skirting or Scotia moulding
• Row width: minimum 80–100mm at walls (avoid very thin cuts at edges — adjust starting row)
• Direction: typically run planks parallel to the longest wall or to the main light source
• Transition strips at doorways, carpet edges, and changes in floor level (maximum 3mm step)
• Not suitable as a 'floating' installation if there is any risk of water ingress from below — a floating floor in a wet room can lift if water penetrates

UFH Compatibility

LVT over underfloor heating requires:

• Fully adhered installation (click/floating systems are not recommended by most manufacturers)
• Maximum floor surface temperature: 27°C (check product datasheet — some specialist products rated higher)
• UFH commissioning before LVT installation: screed must be fully dried and UFH cycled up and down before floor covering is laid
• Use a flexible, thermally-conductive adhesive (check adhesive thermal resistance — should be ≤0.10 m²K/W)
• Never switch UFH from cold to maximum suddenly after laying — ramp up temperature gradually (3°C per day maximum)

Frequently Asked Questions

My client's LVT is curling up at the edges — what went wrong?

Curling is almost always a moisture problem. Either the subfloor moisture was not tested and was too high at time of installation, the adhesive was not the right type for the moisture conditions, or moisture has since entered from below (failed DPM) or from the side (leak, plumbing failure). Diagnose: lift a curl and feel the back — if the adhesive is dissolved or wet-sticky rather than dry and bonded, moisture is the cause. If the bond is otherwise intact, thermal cycling from poorly controlled UFH is the other main cause.

Can I install LVT directly over existing ceramic tiles?

Yes, if the tiles are firmly bonded, flat to 3mm in 1.8m, and the grout joints are no deeper than 1.5–2mm. Fill deep grout joints with a grout float and levelling compound before laying. The additional floor height (LVT + compound) must be accounted for at door thresholds and transitions. Do not lay over cracked or hollow-sounding tiles — these must be removed.

What primer do I need before applying levelling compound?

Most levelling compounds require a primer to prevent the liquid compound from being absorbed too quickly by the subfloor. Use the levelling compound manufacturer's recommended primer:

• Concrete and cement screed: diluted PVA-type or specific penetrating primer
• Anhydrite (calcium sulphate) screed: specific anhydrite primer; seals the surface to prevent adhesion failure
• Plywood: diluted PVA or specific timber primer; all knots must be filled

Never prime and lay immediately — allow primer to fully dry (typically 30–90 minutes).

Regulations & Standards

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

• BS 5325:2015 — Installation of textile floor coverings (not directly applicable but referenced for subfloor prep standards)

• BS EN 14041:2004 — Resilient floor coverings: essential characteristics (product standard for LVT)

• Altro Floors — Technical Guide — commercial LVT installation guidance; moisture testing

• LVT365 — Installation Best Practice Guide — detailed UK guide for contractors

• Karndean — Technical Installation Guide — major LVT brand; free specification guides

• screed types — screed selection and drying times before flooring installation

• levelling compounds — feather-edge and deep-fill levelling for subfloor prep

• underfloor heating tiles — UFH commissioning requirements before flooring

• carpet fitting — alternative soft flooring and subfloor requirements