How do I prepare a subfloor for LVT?

Laminate bridges a small hollow because the boards are rigid. LVT is 2 to 5mm of flexible vinyl that takes the exact shape of whatever it sits on, including a single screw head or a board joint.

What you'll need

• 6mm plywood or hardboard, if overlaying
• Divergent-head flooring screws or ring-shank nails
• Levelling compound and primer
• A long straight edge
• A scraper and a vacuum

Step by step

1. Understand the standard.Most LVT manufacturers want the subfloor flat within about 3mm over 2 metres and, crucially, smooth — no ridges, screw heads, nail heads or board edges standing proud.
2. Identify what you have.Floorboards, chipboard, concrete or an existing floor covering. Each has a different route to an acceptable base and they are not interchangeable.
3. Test for damp first.Do the polythene test on any solid floor before spending money on preparation. Damp comes up through everything you lay on top of it.
4. Over floorboards, overlay.Individual boards move, have gaps, and rarely sit in one plane. 6mm plywood screwed at 150mm centres, or hardboard nailed at 100mm centres, gives a continuous flat base.
5. Stagger and countersink.Stagger the ply joints so they do not coincide with board joints, and set every screw head below the surface. A proud screw head shows through LVT within weeks.
6. Over chipboard, check the sheets are sound.Screw down any loose sheets, replace any that are swollen at the joints, and sand or fill the joint lines. Chipboard often needs no overlay if it is flat and dry.
7. Over concrete, scrape and fill.Remove every lump of plaster and adhesive, fill hollows, and apply a self-levelling compound over the whole floor if it is generally uneven.
8. Prime before levelling compound.The primer controls the suction of the slab. Compound poured onto unprimed concrete dries too fast, pinholes, and can debond.
9. Sand the compound if it has ridges.Levelling compound is not automatically perfect. A quick pass with a sanding block over any trowel lines is worth the ten minutes.
10. Vacuum obsessively.Every grain of grit under a glued LVT shows as a bump forever. Vacuum, then vacuum again after the last preparation step.
11. Acclimatise the tiles.Most LVT needs 24 to 48 hours in the room at the temperature it will be used at, flat rather than stacked on edge, before fitting.
12. Check the underfloor heating schedule.If there is heating in the floor, it must be commissioned, run up and then turned down to the fitting temperature specified. Getting this wrong is a common cause of failure.

Tips

• Hardboard should be laid rough side up for a glued floor and conditioned by damping the rough face and stacking it in the room for 48 hours before laying, or it will dome.
• Run a straight edge over the whole floor before you start and mark every high and low spot with chalk. It takes twenty minutes and directs all the effort where it is needed.
• Click LVT is more forgiving than glue-down, but not much. The flatness requirement is the same; the smoothness requirement is slightly relaxed.

Common mistakes

• Laying LVT straight onto floorboards — Individual boards cup, move independently and have gaps at every joint. LVT is thin enough to take the shape of all of it, so within months you can see every board line and every gap telegraphing through the surface.
• Leaving screw or nail heads proud — A 1mm proud head under a 2mm vinyl tile creates a visible pimple that the foot traffic then wears through. Every fixing has to be below the surface, and this is the most common inspection failure.

If it doesn't work

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