October 25, 2026
Most floors can go over a concrete slab, as long as the slab is dry enough, flat enough and prepared to the installation guide for the floor you choose. Moisture is the big one. Concrete holds water, and too much of it can break down adhesives and cause mould under a floating floor. Here is what to know about flooring over concrete in ground-floor homes and apartments.
Concrete is mixed with water and takes a long time to dry. A new slab can hold moisture for months, and a ground-floor slab can draw moisture up from the ground if the membrane under it is damaged or missing. Moisture rising into a new floor can:
The Royal hybrid and AquaCore guides also say concrete should be cured and at least 60 days old before the floor goes down.
Our installation guides refer to AS 1884, and slab moisture is usually tested as a relative humidity (RH) reading taken in the concrete. Each installation guide sets its own limit. The guides for Royal 6.5mm Premium hybrid, Royal Procore Laminate and our Royal vinyl planks set 75% RH, and so does the Royal 15/4MM Oak guide for glue-down installation.
We test concrete and timber subfloors for moisture free at the measure. If a reading is high, the answer may be more drying time, a moisture barrier or a barrier coating under a glue-down floor. The Royal vinyl plank guide asks for moisture results to be recorded and kept, and the glue-down timber guides need photos of the test and the barrier for any warranty claim.
| Floor | How it goes down | What the guide asks for on concrete |
|---|---|---|
| Hybrid | Floating | 200 micron moisture barrier on all subfloors; underlay is attached to the Royal hybrid boards |
| Laminate | Floating | Underlay with at least a 200 micron moisture barrier, joins taped |
| Engineered timber, floating | Floating | A moisture barrier always, built into the underlay or laid separately, joins taped |
| Engineered timber, glued | Glued where the range allows | A moisture barrier coating before the adhesive |
| Glue-down vinyl | Glued | A smooth, dry slab; a damp proof layer if moisture is high |
| Carpet | Gripper strips and underlay | A dry slab still matters |
Always follow the guide for your range, as the product warranty can depend on it.
Flatness matters more than level. Humps, dips and ridges make floating boards flex and creak and show through thin vinyl. Installers check flatness with a long straight edge. The Royal hybrid guide sets a general limit of 2mm over 1 metre or 4mm over 2 metres, and the Royal vinyl plank guide also checks smoothness with a 150mm straight edge. High spots are ground back and low spots filled with levelling compound, which must be fully dry before the floor goes down. We tell you at the measure if your slab needs levelling.
Hybrid floats over a slab on a moisture barrier. Royal 6.5mm Premium has a 0.5mm wear layer on a waterproof core, Royal Hybrid Pro 9mm has a 0.7mm wear layer on a waterproof core in 1680 x 228mm boards, and Karndean Korlok is a 6.5mm rigid-core plank with 5G click locking. Browse our hybrid flooring or read our hybrid flooring installation guide.
Royal Procore Laminate has extra-long 2265 x 192mm boards with an AC4 surface and over 72 hours of water resistance. RoyalStep Laminate 12mm is our highest-rated laminate at AC5. Our Royal laminates are water resistant, not waterproof. See our laminate flooring.
Royal 15/4MM Oak has a 4mm French Oak top layer and is tongue and groove for floating or trowel-glued installation. Royal AquaCore Oak has a genuine 3mm Oak surface on a water-resistant core with a click-lock system and a 30 year structural warranty. Read our floating timber guide or browse timber flooring.
Royal 3mm Vinyl Plank glues down and is only 3mm thick, so it suits renovations where floor height matters. Karndean LooseLay Longboard is a loose lay plank held by its weight and grip, which can be lifted and replaced, and LooseLay Originals carry a lifetime residential warranty. Karndean’s guide calls for a tackifier in some conditions. See our vinyl flooring.
Carpet goes over a slab on underlay, held by gripper strips at the edges, and the slab still needs to be dry. Living in Queensland’s humidity? Our guide to the best flooring for Queensland homes covers what suits the climate.
Want to know what suits your slab? Book a free measure and quote.
In an apartment, strata rules come first. Many schemes need approval before a hard floor replaces carpet and set acoustic requirements for footstep noise. Royal 6.5mm Premium is rated 6 star acoustic, so it suits apartments. The result in your building also depends on the slab, the ceiling below, the underlay and the installation, and some strata schemes ask for a test report. Check your by-laws, get approval in writing and bring the requirements to us. Our guide to the best flooring for apartments has more.
If your slab has underfloor heating, check the installation guide for the range before you choose. Each guide sets its own conditions for heating, and some floors do not suit some systems. We can go through the guide with you.
Older slabs may still have vinyl, lino or tiles stuck to them, or black adhesive left behind. In homes built or renovated before 1990, these may contain asbestos. Do not sand, scrape or lift them until they have been tested. Once cleared, old adhesive must come off before a glue-down floor goes down.
We test your slab for moisture, check flatness, measure door and threshold heights, and talk through strata rules if you live in an apartment. You get a written quote within two working days of the measure. Royal Floors gives a 2 year installation warranty, and product warranties come from the manufacturer.
For floating floors, yes. The Royal hybrid guide requires a 200 micron moisture barrier on all subfloors, the Royal Procore and RoyalStep laminate guides call for underlay with a moisture barrier, and floating engineered timber always goes on one. Glue-down floors use a barrier coating or damp proof layer where the guide calls for it.
Our installation guides refer to AS 1884, and slab moisture is usually tested as a relative humidity (RH) reading. Many of our installation guides set a limit of 75% RH. We test concrete and timber subfloors for moisture free at the measure.
Not straight away. The Royal hybrid and AquaCore guides say concrete should be cured and at least 60 days old, and the slab must test dry enough for the floor you choose.
Where the range allows it. Royal 15/4MM Oak is tongue and groove for floating or trowel-glued installation. Its guide recommends a moisture barrier coating before the adhesive in every glue-down installation.
It depends on your strata rules. Royal 6.5mm Premium is rated 6 star acoustic, so it suits apartments, but the result also depends on your building’s slab and ceiling. Some strata schemes ask for a test report, so check your by-laws first.
Visit Royal Floors in Penrith, Campbelltown, Hornsby or Logan, or we can bring samples to your home. Book a free measure and quote, including a free moisture test, or call 1300 980 501.
Four showrooms across Sydney & Brisbane
