How to Install SPC Click Flooring on Different Subfloors

Acclimatisation and Site Conditions

SPC flooring is dimensionally stable compared with laminate or solid wood, but it is not immune to temperature. Bring cartons into the room 24-48 hours before installation, leave them flat, closed and stacked no more than four or five high, and keep the room at 18-28 degrees Celsius with 40-65 percent relative humidity. Do not store cartons on edge, do not leave them in a cold van overnight, and do not install into a room that is still drying out from plaster, screed or paint.

All wet trades should be complete, and the building should be weathertight. If the heating or air conditioning is not yet running, the floor will move once it is commissioned, which is why new-build programmes often install flooring after the first heating cycle rather than before it.

Subfloor Rules That Apply Everywhere

Three measurements decide whether the installation will succeed: flatness, moisture and soundness. Flatness should be within 2 mm under a 2 m straightedge, with no steps or ridges. Concrete should read under about 4.5 percent with a carbide moisture meter, or under 75-80 percent relative humidity, and should be at least 28 days old. Plywood and OSB should read under 12 percent. And nothing should be loose: no hollow plaster, no drummy tile, no flaking paint, no wax or oil.

Concrete Subfloors

Concrete is the most common and the least forgiving. Grind or patch high spots rather than trying to bridge them, because a 4 mm plank cannot hide a 3 mm ridge. Fill cracks and control joints, then apply a 2-3 mm self-levelling compound where the slab is genuinely uneven, and let it cure according to the manufacturer, typically 24-72 hours depending on thickness and product. Vacuum thoroughly, then lay a 0.2 mm polyethylene vapour barrier with 200 mm overlaps, taped at the seams, and turn it up the wall 30-50 mm so it sits behind the skirting.

Do not lay over green concrete, and do not assume a floor that looks dry is dry. A slab that has been covered by a screed or an old floor covering may still be releasing moisture for months. If the reading is marginal, specify a surface damp-proof membrane instead of a thin PE sheet.

Ceramic Tile Subfloors

Laying over tile is common in refurbishment and it works well, provided the tile is sound and the surface is made monolithic. Tap every tile: hollow ones must come out and be replaced with patching compound. Fill grout lines and any depressions so the surface is flat and continuous, degrease, and check lippage. A 4 mm SPC plank will telegraph a 2 mm lippage into the joint above it, which is why the fastest reliable route is usually a 2-3 mm skim coat over the whole floor.

A 1 mm difference between tile edges is generally workable with a 5 mm plank and an attached pad; beyond that, skim it. Also remember that the new floor is only as stable as the tile underneath, so a wall that is moving or a floor with drummy areas is not a candidate for covering up.

Plywood and OSB Subfloors

Timber subfloors are usually the easiest to make flat, but they have their own rules. Use a minimum of 15-18 mm plywood or OSB, screw it at 150-200 mm centres, stagger the joints and offset them from the joist lines below, and leave 2-3 mm gaps between sheets for movement. Do not use particle board or MDF, which swell and lose strength when they get damp.

Fix any squeaks or deflection before the flooring goes down; deflection should not exceed about 1/360 of the span. On an upper floor over a heated space, a vapour barrier is usually unnecessary, but on a ground floor over a crawl space or a slab, it is cheap insurance. If the plywood is dusty or sealed with a glossy finish, clean and lightly sand it so the plank joints can settle evenly.

Underlay and Vapour Barrier Rules

Most export SPC planks come with a pre-attached 1-1.5 mm IXPE or EVA acoustic pad, and the most common installation mistake in the trade is adding a second foam layer on top of it. Double underlay makes the click joints flex, and flexing joints open and squeak. If the plank has an attached pad, lay it directly on the prepared subfloor or on the vapour barrier, and nothing else.

Where an acoustic specification applies, typically an 18-21 dB impact reduction requirement, choose a plank with a thicker attached pad or use a specified 1-1.5 mm underlay rather than a soft 3 mm foam. A soft, thick underlay feels comfortable for a week and then causes joint failure for the next ten years.

Expansion Gaps and Layout

1. Measure the room and decide the plank direction, usually along the long axis of the room or toward the main light source.
2. Undercut door frames and architraves so planks slide underneath with a clean edge.
3. Install 5-8 mm spacers along every wall, column, pipe and fixed object.
4. In large areas, allow 10-12 mm and split any run longer or wider than about 10-15 m with a transition profile.
5. Use a T-moulding at doorways and where the floor meets another floor material or a fixed threshold.
6. Keep the floor floating: never screw, glue or nail planks down, and never trap the floor under kitchen islands, fitted wardrobes or cabinets fixed to the wall. Fit the floor first and cut around them, or install a movement joint.
7. Work in rows of three or four planks, staggering end joints by at least 200-300 mm, and avoid creating a staircase or cross-joint pattern.

Installation Sequence

1. Empty the room, remove the old floor covering if specified, and check the subfloor with a straightedge, a moisture meter and a tap test.
2. Prepare the subfloor: grind, patch, level, vacuum, and allow any compound to cure fully.
3. Lay the vapour barrier with taped overlaps, if required, and fit spacers along the starting wall.
4. Start in a corner with the tongue facing the wall, and click the first row together end to end.
5. Cut the last plank of each row, and use the offcut to start the next row if it is at least 200-300 mm long.
6. Click each new row into the previous one at a low angle, then press down until the joint closes with a soft click; use a tapping block with a pull bar near walls.
7. Check every few rows for square and for joint tightness, and check the expansion gap is still open.
8. Cut the final row to width, fit transition profiles at doorways, remove the spacers, and fit skirting or a beading that allows the floor to move.

Common Mistakes and How They Fail

• No expansion gap: the floor peaks or buckles against walls and door frames within weeks.
• Subfloor out of tolerance: click joints open, the floor sounds hollow and the locking lip can crack.
• Double underlay: joints flex underfoot and open permanently.
• Insufficient acclimatisation or installation in the cold: end joints gap as the planks shrink.
• Heavy point loads from appliances, piano legs or pallet trucks: permanent indentation.
• Laying over a wet slab: mould, warping and eventual failure of the click system.
• Wet mopping within the first 24 hours: water drives into the joints and weakens them.
• Kitchen units or wardrobes installed on top of the floating floor: the floor is pinned and cannot move.
• Door clearance under 8-10 mm: the plank drags on the door and the joint lifts.

Output, Wastage and Aftercare

Two installers typically lay 30-50 square metres per day in a clear rectangular room, and 15-25 square metres per day in a cut-up area with many doorways and columns. Allow 5-10 percent waste and keep one spare carton per 50-80 square metres on site for future repairs and colour matching.

After installation, keep the floor dry for 24 hours, clean with a damp mop and a pH-neutral cleaner, and never use a steam mop above about 60 degrees Celsius. Fit felt pads under furniture legs, use entrance mats at external doors, and re-check the expansion gaps after the first heating season, because that is when any trapped floor shows itself.

Where SPC Click Flooring Should Not Be Used

Avoid fully wet rooms with a floor drain, saunas and steam rooms, permanently damp basements without a damp-proof membrane, outdoor areas, and rooms that are regularly below about 5 degrees Celsius or above 40 degrees Celsius without climate control. In those conditions a floating floor will move beyond its design range and the joints will take the damage.

Almost every failed SPC floor can be traced to three checks that were skipped: flatness, moisture and expansion gaps. Do those three properly and the product rarely gives trouble.