Why Old Floorboards Need Attention Before Vinyl Goes Down

Vinyl is a wonderful choice for an older home. It is warm underfoot, simple to clean and tough enough to cope with muddy boots and busy kitchens. It is also, unfortunately, one of the most unforgiving floor coverings you can lay over original boards. Sheet vinyl and luxury vinyl tiles are thin and flexible, so they will mirror every dip, ridge and lifted nail head beneath them. Left uncorrected, those imperfections telegraph through the surface within weeks, and the covering will eventually split, curl at the edges or wear through in the hollows.

The good news is that the preparation is entirely achievable. Old floorboards simply need to be sound, flat and free from anything that protrudes. Once you have that, a thin plywood overlay or a smoothing compound gives the vinyl the stable, uniform surface it needs to perform for years.

Inspecting the Boards: Soundness, Movement and Protruding Nails

Before you buy a single bag of compound, spend an hour on your hands and knees. Press down on each board with the heel of your hand and listen. A board that flexes or clicks is moving, and movement is the enemy of a vinyl installation.

• Loose boards: re-fix them with countersunk wood screws rather than nails. Screws hold far better and can be tightened later if needed.
• Protruding nails: punch every visible nail head below the surface with a nail set, then drive a screw alongside it. A single proud nail can puncture sheet vinyl or lift a tile.
• Split, rotten or damaged boards: cut out the affected section and replace it with timber of a similar thickness. Do not be tempted to fill large voids with compound alone.
• Squeaks and gaps: a light sprinkle of talcum powder worked into the gaps between boards can quieten minor squeaks.
• Existing adhesive or paint: scrape off lumps of old glue, paint drips and hardened filler, as these create high spots.

If the boards are badly cupped, twisted or simply too far gone, it is usually quicker and cheaper to overboard than to attempt a rescue.

How Flat Is Flat Enough?

Flatness matters far more than levelness. Your floor does not need to be perfectly horizontal, but it does need to be free of sudden changes in height. As a practical rule, aim for no deviation greater than 2mm over any 2m straight edge, and nothing sharper than a gentle slope at the joints. Anything steeper will show through the vinyl as a visible line or cause the covering to bridge and eventually crack.

Check with a long straight edge or a spirit level laid in several directions across the room. Mark every hollow and hump with chalk so you can deal with them methodically rather than chasing problems as you lay the vinyl.

Plywood Overlays: The Dependable Option

For most old floorboards, a plywood overlay is the most reliable route. It bridges gaps, spreads load and creates a smooth, dimensionally stable surface that adhesive can grip properly. Use exterior-grade plywood at least 5.5mm thick for sheet vinyl, or 6mm and above where the boards are uneven or the room sees heavy traffic.

Fit the sheets with the grain running across the floorboards, staggered so that no four corners meet in a cross. Leave a small expansion gap of around 2–3mm between sheets and a 5mm gap at the perimeter, then fix with screws at roughly 150mm centres along the edges and 200mm across the centre, sinking every head flush or just below the surface. Always screw into the joists where you can, and stagger the joints away from the underlying board joints. Once fixed, fill the screw heads and sheet joints with a fine filler and sand smooth.

Smoothing Compounds and Filling Gaps

Where the boards are reasonably sound and you would rather not raise the floor height, a smoothing compound can do the job. First fill any wide gaps between boards with a flexible filler or strips of timber, because compound will simply drain through them. Prime the surface with the recommended primer — usually two coats on bare timber — and let it dry fully.

Mix the compound to a smooth, lump-free consistency and pour it in sections, spreading with a steel trowel or squeegee. Work in bands rather than dollops, and keep the thickness within the manufacturer's limits, typically up to 3–5mm per application. Feather the edges so they blend into the surrounding boards. Once cured, sand any ridges and vacuum thoroughly. A dusty floor will not accept adhesive.

Getting the Conditions Right Before You Start

Preparation is not finished until the room is ready. Acclimatise the vinyl in the room for at least 24 hours, ideally 48, at a steady temperature between 18°C and 24°C. Timber and vinyl both move with moisture and heat, so let them settle together.

Check the subfloor moisture content if you are working at ground level, and fit a suitable damp-proof membrane if readings are high. Vacuum the prepared surface twice, then prime it if the adhesive requires it. Only then should you start laying.

Take your time over these steps. A day spent screwing down boards and smoothing joints is a small investment compared with lifting a failed floor and starting again — and it is the difference between a vinyl floor that looks tired in a year and one that still looks sharp a decade from now.