There Is No 'Perfect' Karndean Installation
If you're a contractor or specifier looking for a single, universal answer on how to fit Karndean LVT, I'm going to disappoint you. The honest truth—the one that keeps my job interesting—is that the right installation method depends almost entirely on your subfloor.
I review roughly 200 unique installs annually for our distributor network. In Q1 2024 alone, I rejected 12% of first deliveries because the specified fitting method didn't match the documented subfloor conditions. That's not failure on the installer's part; it's often a mismatch in the planning phase.
Let's break it down into the three most common subfloor scenarios I see. If you're dealing with something outside these, your experience might differ. But for 80% of commercial and high-end residential projects, this framework applies.
Scenario A: Concrete Subfloor (New Build or Major Renovation)
This is the most straightforward case, but it's also where I see the most seemingly trivial mistakes. For concrete, I almost always recommend a glue-down system like Karndean Korlok or a standard glue-down LVT, depending on your moisture risk.
What most people do right: They check for moisture. They use a moisture meter. Good.
What most people miss: The concrete's smoothness. I've seen installs where the slab was within industry standard for flatness—say, 1/8" over 10 feet—but the LVT's locking system clicked and popped because of microscopic ridges. The issue wasn't the floor; it was the surface profile. We rejected a batch of 800 sq ft of Karndean Van Gogh last year because the concrete was smooth to the touch but had a 60-grit sandpaper texture that prevented full adhesive bond. The cost to grind and re-level was roughly $1.50/sq ft—an expense the client hadn't budgeted.
My advice: Test the concrete surface with a straightedge, and a fingernail. If your nail catches on a ridge, you need a skim coat. Also, don't assume a moisture vapor emission rate (MVER) test from six months ago is still valid. Retest. I learned this the hard way in 2022 when a storage facility's slab had shifted moisture levels after a wet winter.
Scenario B: Multi-layer Subfloor (Plywood Over Existing Concrete or Old Timber)
This is the situation that gives me the most pause. You're often dealing with an older building where someone has installed a plywood layer over concrete to create a level surface, or you're over an old timber floor.
Here, I lean toward a loose lay system like Karndean Looselay. Why? Because you're introducing an expansion and contraction risk. A glue-down system on a plywood subfloor in a climate-controlled space is fine, but if the space has seasonal humidity swings, the plywood will move. Loose lay LVT can float and accommodate that movement without buckling or gapping.
The counterintuitive part: Most installers assume a click-lock system works best over plywood because it feels more 'locked in.' In my experience, click-lock over a multi-layer subfloor creates stress at the joints if the plywood panels shift unevenly. I've seen a 1,200 sq ft commercial office space where the click-lock planks started separating at the seams within 6 months. The cause? The underlying OSB panels had a 2mm vertical movement due to minor swelling.
What I check for: I run a simple deflection test—stand on the subfloor, jump gently (yes, actually jump). If I feel any 'give' or hear a creak, I automatically default to loose lay. Not ideal for everyone, but it's the most forgiving method for inconsistent substrate movement.
Scenario C: Heated Subfloor or Floating Over Existing Tile
This is the niche scenario I get asked about most often. You have a subfloor with underfloor heating, or you're installing directly over an existing ceramic tile floor that's in good condition.
For heated floors: Forget glue-down. The heat cycles will cause the adhesive to soften and the LVT to shift. Use a click-lock rigid core system like Karndean Rigid Core. The rigid core handles the temperature range (typically 80-105°F in the slab) significantly better than flexible LVT, which can curl or soften.
For existing tile: I've only worked with this on about 40 projects, so take this with a grain of salt. But my recommendation is to use a full-spread adhesive on the tile surface after thoroughly cleaning and applying a primer. Do not try to install LVT over tile with a loose lay system—the grout lines will telegraph through the planks within a year. You'll see the pattern. I saw it on a restaurant project where the owner insisted on saving time by skipping the primer. The grout line made a 1/32" elevation change that was visible in every seam.
How to Determine Which Scenario You're In (Before You Start)
The mistake I see most frequently is installers deciding on the product and system before they've fully characterized the subfloor. Here's a simple checklist I give our distributors:
- Moisture test: If MVER > 5 lbs/1000 sq ft/24hr, use a vapor barrier with glue-down or choose a loose lay system rated for high moisture.
- Flatness check: Use a 6-foot straightedge. If you find more than a 1/8" gap, you need leveling compound, regardless of the system.
- Movement test: Jump test. If the floor 'gives,' switch to loose lay or rigid core click.
- Temperature source: If there's underfloor heating, the product spec must state it's compatible. Most Karndean rigid core and some glue-down products are fine up to 80°F surface temp.
This was accurate as of Q1 2025. The flooring industry—especially adhesive technology—changes fast. Verify current product specs before committing, especially for specialized projects like heated floors or unusual subfloor materials.
