Short answer: a quality hybrid plank will ride out small undulations in a subfloor — roughly 3 mm of variation over a 2 m span — but it won’t fix a slab that’s genuinely out of level. If you’ve got a hump, a dip, or a slope, the rigid SPC core will telegraph it through and the click joints will work themselves apart over time. This guide covers what hybrid can and can’t handle, what to do about the rest, and how to set the floor up so it stays tight years after the install.
Why hybrid handles minor unevenness at all
Hybrid planks are built around a rigid stone polymer composite (SPC) or wood polymer composite (WPC) core. That core gives the plank stiffness across its length, so the plank itself doesn’t flex into a low spot the way a thin laminate or sheet vinyl would. Most ranges also come with a pre-attached IXPE acoustic backing, which absorbs the very small surface variations you can’t see with the naked eye but feel underfoot.
That’s the upside. The downside is that the same rigidity means hybrid won’t bend gracefully across a real dip. If a 100 mm-wide low spot sits under a click joint, the joint has nothing to sit on, the plank rocks, and the lock eventually fails. For more on the joinery itself and why it matters here, see our explainer on 5G and 2G clicking systems.
The tolerance to aim for
Most hybrid manufacturers specify subfloor flatness within 3 mm over a 2 m straight edge. That’s the rule we work to on our installs. To check it yourself:
- Lay a 2 m aluminium straight edge or a long spirit level on the subfloor.
- Slide a 3 mm packer underneath at any point along the length.
- If the packer fits without lifting the straight edge anywhere else, the gap is over-tolerance and that area needs work.
- Walk the room in a grid pattern — corner to corner, then along each wall — not just down the middle.
Older Australian slabs, especially in homes built before the mid-1990s, often fail this check around the perimeter where the slab dips toward the edge form. Timber subfloors fail it where joists have moved or where a sheet seam has lifted.
When you need to fix the subfloor first
If the variation is more than 3 mm over 2 m, you’ve got a few options depending on what the subfloor is and what’s causing the problem.
Concrete slabs
Self-levelling compound is the standard fix. It’s a cement-based pourable product that finds its own level and sets hard within hours. For a typical Australian living area, expect to use 2-4 mm depth across the worst zones, primed first. High spots can be ground down with a concrete grinder rather than poured around. We’ve covered the broader picture of laying over slabs in our guide on whether you can lay vinyl on a concrete floor.
Timber subfloors
If the boards or sheets have moved, screw them back down to the joists first — nails alone won’t hold long-term under a click floor. Sand any lifted seams flat. For larger dips, a 6 mm plywood underlayment over the existing floor evens out the surface and gives the hybrid a consistent base. Don’t try to fix timber subfloor humps with self-leveller; the cement product moves with the timber and cracks.
Underlay won’t save you
A common mistake is layering a thicker foam underlay over an uneven slab, hoping it’ll cushion out the dips. It won’t. Foam compresses under load, the plank still rocks, and the warranty’s voided as soon as you put a non-spec underlay under hybrid. Hybrid planks with pre-attached IXPE shouldn’t have any additional underlay added at all. We’ve written a separate piece on whether you need underlay for vinyl flooring that’s worth reading before you order anything extra.
When hybrid is the wrong call
If your slab has a structural slope — say it falls 20 mm from one side of the room to the other — that’s not a flatness problem, it’s a level problem, and no floor finish will hide it. The fix is to grind, screed, or in extreme cases topping the slab. If you’ve got rising damp or a moisture issue under the slab, that needs to be sorted before any click floor goes down. Hybrid is waterproof from above, but moisture coming up from below will still de-bond the IXPE backing over time.
The bottom line
Hybrid is forgiving for minor undulation, not for genuine slope or large dips. Check the subfloor with a 2 m straight edge before you order anything, fix anything outside 3 mm tolerance, and don’t try to compensate with thicker underlay. Done properly, a hybrid floor on a prepared slab will stay tight for the life of the wear layer. If you’d like a hand sizing up the right product for your subfloor, our Sydney and Brisbane showrooms stock the full Aqua Stone range, and you can see how it sits against the rest of our line-up in the best hybrid flooring brands in Australia guide.
Ready to shop? Browse our full hybrid flooring range online, or drop into our Sydney or Brisbane showroom to see the range in person.
Frequently asked questions
It rides out small undulations, roughly 3mm of variation over a 2 metre span. It will not fix a hump, a dip or a genuine slope; the rigid core telegraphs those through and the joints eventually work apart.
Lay a 2 metre straight edge across the floor in several directions and try to slide a 3mm spacer underneath. If it fits anywhere, that spot needs levelling before the floor goes down.
Grind the high spots and fill the low spots with a self-levelling compound, then let it cure before laying. On a timber subfloor, sheeting with plywood is often quicker than chasing individual boards.