How to Prep a Subfloor for LVT — Don't Skip This Bit, Mate
How to Prep a Subfloor for LVT — Don't Skip This Bit, Mate
If there's one thing I've seen wreck an otherwise decent LVT installation, it's a subfloor nobody bothered to prepare properly. I've been fitting floors in Essex since 1982 and I can tell you: nine times out of ten, a floor that fails within the first year failed because of what was — or wasn't — done underneath it.
LVT (luxury vinyl tile or plank) is brilliant stuff. Warm underfoot, incredibly tough, and it looks genuinely good. But it's brutally unforgiving of lumps, hollows, damp and movement. A 3mm dip you'd never notice walking across in socks becomes a creak, a gap or a buckled plank six months in. And then you're paying twice.
Here's what I do on every job. Take notes.
Step 1: Clear the Room and Assess What You've Got
Before anything else, get the room cleared — all furniture, all appliances, all excuses. Then get on your hands and knees and look across the floor at a low angle. You're checking for high spots, low spots, flex, creaking boards, and anything that moves when you press it.
If you've got a timber subfloor (suspended floor with joists):
- Walk every inch. Any bounce, flex or squeak means a board or joist needs attention before you lay anything.
- Nail or screw down any boards that move. I use screws — they pull tight and stay tight, unlike nails that gradually work loose.
- Fill gaps between boards with a flexible filler.
- If boards are cupped, warped or badly uneven, lay 6mm or 9mm WBP (exterior-grade) plywood over the top. Don't cheap out on the ply — interior-grade softens with any moisture and you'll feel it through the floor.
If you've got a concrete or screed subfloor:
- Tap across the surface with your knuckle and listen. A hollow sound means the screed has delaminated underneath — loose areas need cutting out and refilling before you do anything else.
- Check for any soft or powdery patches and treat them accordingly.
Step 2: Deal With Moisture — Seriously, Don't Skip This
This is the one homeowners always want to rush. I understand — you've waited weeks for the floor, you want it done. But LVT, even though it's waterproof on the surface, does not enjoy sitting on a damp subfloor. Moisture in screed or concrete can cause adhesive failure, bubbling and mould growth where you can't see it until it's too late.
The plastic sheet test: Tape a piece of polythene (about 300mm × 300mm — roughly a foot square) to the floor with duct tape on all four edges. Leave it for 24 to 48 hours. If there's condensation on the underside when you peel it back, you've got a moisture problem that needs addressing first.
Most screed should have a moisture reading below 75% relative humidity. If yours is higher, you'll need either to wait longer or apply a moisture-suppressing primer or membrane before laying.
New screed rule of thumb: allow at least one day of drying time per millimetre of depth. A 50mm (2-inch) screed needs at least seven weeks before you fit flooring over it. Rush this and you will regret it — and I'll be back charging you to relay everything.
Step 3: Get the Floor Flat
LVT manufacturers typically specify a maximum variation of 3mm over a 1.8m (6ft) span. Some premium ranges are stricter. If your floor is outside this tolerance, the LVT will mirror every bump and hollow — and it gets worse over time, not better.
Use a self-levelling compound (SLC) to fill hollows and smooth dips. A quality SLC from a trade supplier, properly mixed, flows into low spots, can be feathered to almost nothing, and is walk-on in 30 to 60 minutes. Don't use ordinary filler — it's not designed for this.
For high spots on screed, grind them down. On timber, plane or sand flat first, then feather over anything remaining with SLC.
Get yourself a 2m (6ft 6in) straight edge — a good aluminium spirit level does the job. Run it across the floor in multiple directions and mark any problem areas with chalk before you start filling.
Step 4: Prime the Surface
Once the SLC has fully cured (check the product datasheet — don't guess), apply a floor primer. This seals the surface, dramatically improves adhesion, and stops the compound powdering off under the LVT. One coat, let it go tack-dry, and you're ready.
For floating (click-lock) LVT, you can often go straight over a well-prepped floor without adhesive — many ranges will specify this. For glue-down LVT, the primer is not optional; the adhesive needs a solid, sealed surface to key into properly.
Step 5: Let the LVT Acclimatise
Leave the boxes of LVT in the room for at least 24 to 48 hours before you start fitting. This matters most in winter, when LVT comes straight from a cold van into a warm room and can expand after laying. Give it time to reach room temperature first.
The Bottom Line
Every corner you cut on subfloor prep shows up later — in your floor, and in your bank account when you're paying to have it redone. A properly prepped floor takes longer and costs a bit more in materials. But it's the difference between a floor that looks brilliant after five years and one that's lifting at the edges before the year is out.
If you're planning an LVT installation in Essex and you're not sure what state your subfloor is in, WhatsApp me before you order a single plank. Five minutes now saves a proper headache later.
For an idea of how much flooring you'll need before we even get to the subfloor question, the flooring calculator at HowMuchDoINeed.co is worth a look — and their room measuring guide will help you get the numbers right before you call anyone.
I cover LVT and subfloor work across Essex, including Chelmsford, Basildon, Billericay and the surrounding villages.
Frequently asked questions
How flat does a subfloor need to be for LVT?
Most LVT manufacturers specify a maximum variation of 3mm over a 1.8m (6ft) span. Go outside that and the LVT will telegraph every lump and hollow, and it only gets more noticeable over time. Use a self-levelling compound to fill any dips and grind down any high spots.
Can I lay LVT on an uneven floor?
Not if you want it to last. LVT is rigid enough to mirror every bump underneath it and flexible enough to rock over hollows. Both lead to cracking, lifting or visible dips. Sort the subfloor first — it's not optional.
How long do I need to wait after screeding before laying LVT?
As a rule of thumb, allow at least one day of drying time per millimetre of screed depth. A 50mm screed needs at least seven weeks. Fit over it too soon and moisture will cause adhesive failure or bubbling — often where you can't see it until the damage is done.
Do I need to prime before laying LVT?
Yes, especially for glue-down LVT. Priming seals the surface, improves adhesion and stops any self-levelling compound powdering off under the floor. For floating click-lock LVT it's less critical but still good practice on porous or dusty surfaces.
Can I lay LVT directly on a timber subfloor?
Yes, but only once the boards are screwed tight, all movement has been eliminated, and the surface is flat. If there's any flex or unevenness, lay 6mm or 9mm WBP plywood over the top first. Skipping this step is the most common cause of LVT failure on timber floors.
Want a hand with your floors?
Message Graham on WhatsApp with a few details about your rooms and what you’re after.