Vinyl Plank and LVT Flooring: Substrate Prep, Expansion Gaps and Fitting Methods

Quick Answer: Modern vinyl plank flooring (LVT, SPC and rigid-core click) requires a substrate flat to within 3mm under a 2m straightedge, fully dry (≤75% RH per BS 8203), and acclimatised on site for at least 48 hours. Glue-down LVT needs a 5mm minimum perimeter expansion gap; click-fit and SPC need 8–10mm. The most common cause of post-installation failure is omitted or inadequate moisture testing on screed and concrete substrates — always hygrometer-test before fitting.

Summary

Vinyl plank is the fastest-growing flooring category in UK domestic refurbishments. It looks like timber, costs around half as much as engineered hardwood, handles bathrooms and kitchens that timber cannot, and most products carry a 15–25 year residential warranty. The category covers several construction types — flexible LVT, rigid-core SPC, hybrid WPC and click-engineered vinyl — and the installation method changes with each.

The market split between glue-down LVT and click-fit rigid core has shifted toward click in domestic settings (faster install, no adhesive smell, removable for repair) and stayed with glue-down in commercial and high-traffic settings (better dimensional stability, no expansion gap requirement, longer life under heavy castor wheels). Choosing the wrong type for the application is one common failure mode; the bigger one is ignoring the substrate flatness and moisture requirements.

This article covers the substrate preparation, moisture testing, layout and installation method for both glue-down and click systems, plus the expansion gap and edge detail rules. For the related article on full LVT installation see the LVT installation overview and on screed substrates the screed types and drying article.

Key Facts

Quick Reference Table

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Plank Type Thickness Method Best For Lifespan
Flexible LVT (glue-down) 2.0–3.0mm Full-spread adhesive Commercial, high-traffic, wet rooms 15–20 years
Flexible LVT (loose-lay heavy) 4.5–5.0mm Friction-fit, perimeter glue Office, retail 15–20 years
Click LVT (rigid HDF core) 5–7mm Click-fit floating Domestic dry rooms 15–25 years
SPC (stone polymer) 4–8mm Click-fit floating Domestic kitchens, bathrooms, all rooms 20–25 years
WPC (wood polymer) 6–8mm Click-fit floating Domestic mid/upper floors, bedrooms 15–20 years
Substrate Prep Required Moisture Test
Sand/cement screed Smoothing compound if not SR2; DPM if no integral Hygrometer ≤75% RH (BS 8203)
Anhydrite (calcium sulphate) screed Sand surface laitance, prime, smoothing compound Hygrometer ≤75% RH; carbide bomb ≤0.5% CM
Concrete DPM, smoothing compound, prime Hygrometer ≤75% RH
Plywood / OSB Joints filled and sanded; minimum 6mm Moisture content ≤14%
Existing tile/stone Smoothing compound at depth to fill grout lines; check for hollow tiles Visual + cover existing DPM if present
Existing timber floorboards Overlay with 6mm plywood; not direct Visual inspection for movement
Existing vinyl/lino Lift unless certified bonded; if leaving, check no asbestos Visual

Detailed Guidance

Substrate Preparation — Where Most Vinyl Floors Fail

The single biggest cause of vinyl plank failure is laying onto a substrate that is not flat or not dry enough. Both faults show up months later — flatness defects telegraph through as visible humps and seam failures; moisture defects cause cupping, edge lifting, adhesive failure and sometimes mould.

Flatness:

Modern click-fit rigid-core vinyl tolerates more substrate variation than glue-down LVT, but only just. The standard test is a 2m straightedge laid in any direction across the floor. Under a 2m straightedge:

Out-of-flat substrate either gets levelled with cementitious smoothing compound (over concrete or screed) or, for small dips, plywood overlay. Don't try to "make it work" with thicker underlay or extra adhesive — both will fail.

See the floor levelling compounds article for product selection and depth limits.

Moisture:

BS 8203:2017 requires moisture testing on every concrete or screed substrate before installing any resilient floor covering, including vinyl. The accepted method is a digital hygrometer in a sealed insulated hood (Wagner, Tramex or equivalent), left in place for the manufacturer's specified equilibration time (typically 4–72 hours). The reading must be ≤75% RH.

For anhydrite (calcium sulphate) screeds, the carbide bomb (CM test) is also acceptable: ≤0.5% CM.

Skip the test and you are gambling with the installation. New screeds dry at roughly 1mm per day for sand/cement (so 75mm screed = 75 days to dry), and slower for liquid screeds in poorly ventilated rooms. Moisture-related failures are not covered by manufacturer warranties and the cost of strip-and-relay falls back on the installer.

Acclimatisation — 48 Hours, Flat, In the Room

Vinyl plank arrives off the lorry at whatever temperature it has been stored at — often 5–10°C in winter or 25°C+ in summer. Installing immediately means the planks expand or contract after install, opening seams or buckling.

Standard practice for all vinyl plank types:

Air conditioning, dehumidifiers and open windows can all undermine acclimatisation. Aim for stable, normal-occupancy conditions.

Layout and Setting Out

Vinyl plank looks best laid in the dominant light direction (planks running away from the main window). Practical setting-out steps:

  1. Identify the longest wall that the planks will run parallel to.
  2. Find the room centre line and check that the planks fit equally on both sides — calculate the strip width needed at the start and end. If the end strip would be less than half a plank width, shift the centre line so both ends finish at sensible widths.
  3. Check for wall straightness — if walls are out of square (older properties commonly have walls 10–25mm out over a 4m run), scribe the first row to follow the wall rather than running planks at an angle.
  4. Stagger the joints — minimum 200mm offset between end joints in adjacent rows; 300mm preferred. Avoid step patterns (where every third row aligns) and H-patterns.
  5. Mix planks from at least three packs as you fit — colour and grain printing varies between batches; mixing prevents visible bands.

Installing Click LVT, SPC and WPC

  1. Underlay (if required) — roll out perpendicular to plank direction; tape seams with manufacturer-specified tape. Do not use carpet foam underlay.
  2. First row — place planks tongue-side to the wall, with 8–10mm spacers maintaining the expansion gap. End-joint by tilting the next plank into the previous one's short edge and clicking down.
  3. Subsequent rows — start with the offcut from the previous row (provided it is 200mm+); tilt the long edge into the previous row, slide along until the short joint engages, then click down.
  4. Tapping block — use a manufacturer-supplied or polymer tapping block and rubber mallet. Never strike the plank edge directly with metal — it damages the click profile and ruins the seam.
  5. Around obstacles — cut planks with a sharp utility knife (score-and-snap on flexible LVT) or jigsaw on rigid SPC. Heat the underside with a hot air gun for tight curves.
  6. Last row — measure and cut to maintain the perimeter expansion gap; pull into place with a pull bar at the wall.
  7. Skirting and beading — fix to the wall (not to the floor); cover the expansion gap. Do not silicone the floor edge to the skirting — that defeats the floating-floor function.

Installing Glue-Down LVT

  1. Prime substrate if specified by adhesive manufacturer — improves bond and seals porous substrates.
  2. Set out as above; mark a working line.
  3. Mix and apply adhesive with the specified notched trowel (typically A2 1.5mm for permanent acrylic on smooth substrate). Spread to manageable area — typically 3–5m² per working batch depending on adhesive open time.
  4. Open time — pressure-sensitive acrylics need 15–30 minutes flash-off (transparent finger test) before laying tiles.
  5. Lay tiles into the adhesive with a sliding action, butting tightly to previous tile. Roll with a 50–70kg three-section roller in two directions immediately after laying — once with the planks, once across.
  6. Working time — most pressure-sensitive adhesives have 60–90 minute working time; do not lay into adhesive that has skinned.
  7. Cure — allow 24 hours minimum before traffic, 48–72 hours before heavy furniture or rolling loads.

Underfloor Heating Compatibility

Most modern vinyl plank is rated for use over wet underfloor heating provided:

Glue-down LVT generally tolerates higher temperatures than click systems because the adhesive bonds to the heated screed, eliminating the expansion-gap issue.

For electric heating mats under vinyl, only use systems specifically rated for vinyl over them — generic underfloor mat systems can localise hot spots that exceed the vinyl's temperature rating.

Wet Areas — Bathrooms and Kitchens

SPC and waterproof-rated LVT can be used in bathrooms but the perimeter detail must address water ingress:

For tile/grout-equivalent finishes in bathrooms see the wet room construction article.

Common Defects and Their Causes

Defect Likely Cause
Edges curling up Substrate moisture above 75% RH; missing DPM
Seams opening over time Insufficient expansion gap; perimeter sealed/pinned
Visible undulation at substrate transitions Substrate not levelled to SR2; smoothing compound omitted
Click joints separating Floor pinned at perimeter or to fixed objects (toilet, kitchen unit)
Adhesive showing at seams Over-application of adhesive; failed to use specified notched trowel
Plank cracking under castor wheels Wrong product (click LVT, not glue-down); inadequate substrate support
Discolouration / yellowing UV exposure; rubber underlay leaching plasticiser; cleaning chemicals

For diagnostic decision tree on existing vinyl floor failures see the vinyl floor diagnostic (in queue).

Frequently Asked Questions

Can I install vinyl plank over existing tiles?

Yes, if the tiles are well-bonded, level (no hollow tiles, no lippage between tiles greater than 1mm), and the grout lines are filled with smoothing compound to give an SR2 surface. Tap each tile with a metal hammer handle — hollow sounds mean failed bond and the tile must come up. The smoothing compound depth needed is typically 3–5mm to fill grout lines to a flat finish. Don't lay vinyl directly onto tile without filling the grout lines — they telegraph through within months.

Do I need an underlay under SPC?

SPC products often have an attached IXPE or cork underlay on the back — in which case no separate underlay is needed (and adding one will void warranty by exceeding the manufacturer's compressibility spec). For SPC without attached underlay, use a 1.5–2mm dedicated SPC/click vinyl underlay — never traditional carpet foam or 5mm+ premium underlays designed for laminate. The compressibility tolerance of click systems is much tighter than laminate.

How do I cut vinyl plank cleanly?

Flexible LVT scores cleanly with a sharp utility knife — score the surface with a metal straightedge, snap upward over an edge, then cut the backing. SPC and rigid LVT need a fine-tooth jigsaw, mitre saw or dedicated vinyl plank shear. For cuts around toilets, pipes and complex shapes, make a paper template first, transfer to the plank, and cut with a jigsaw. Heat the underside with a hot air gun for tight curves on flexible LVT. Always cut with the decorative side up to keep the visible edge clean.

Will vinyl plank devalue my house compared to engineered hardwood?

Premium SPC and click LVT in current realistic wood reproductions are now broadly accepted in mid-market UK property valuations, particularly in kitchens and bathrooms where solid timber is not appropriate. Surveyors and estate agents increasingly distinguish "quality vinyl" from "cheap laminate". For period properties, listed buildings and prime-end housing, traditional materials still command a price premium. For typical UK family housing, well-fitted SPC in a quality finish does not reduce value — and may add appeal in family homes where durability and water-resistance matter.

Can I lay vinyl plank in a conservatory?

Manufacturer-specific, but most click LVT and SPC are not warranted for conservatories because of the temperature swing — conservatory floor temperatures can drop to 5°C in winter and exceed 30°C in summer, exceeding the dimensional stability range of most click products. Solutions: glue-down LVT (better tolerance because adhesive constrains movement); or specifically conservatory-rated SPC products from manufacturers like Karndean Knight Tile or Amtico Spacia ranges. Always check the manufacturer's stated installation temperature range against your conservatory's actual swing.

Regulations & Standards