The short answer
To install solid oak parquet over a concrete slab in Australia, the slab must be flat (commonly within about 3mm under a 3m straightedge), clean, sound and dry enough for the chosen adhesive; the blocks are then glued directly to the slab, usually with a moisture barrier or a moisture-barrier adhesive. The adhesive manufacturer's limits and instructions govern (Bowens).
This guide outlines common Australian practice for 18mm solid European oak parquet such as Timbo's herringbone and chevron. It is not a substitute for the adhesive, barrier and finish manufacturers' instructions or for relevant standards – where they differ from this guide, they apply.
Why slab preparation matters so much
Most failures of glued timber floors – cupping, lifting, hollow-sounding blocks and gaps – trace back to slab moisture, poor flatness or poor bond. Solid oak moves as it gains and loses moisture; a damp slab feeds moisture into the underside of the blocks, and an uneven slab leaves voids where the adhesive can't bond.
A useful mental model: the slab, the barrier, the adhesive and the timber are one system. Change one part and the others must still be compatible.
Step 1: Assess the slab
Check flatness, moisture, surface strength and contamination before ordering adhesive.
| Check | What to look for | Typical action |
|---|---|---|
| Flatness | Deviations under a 3m straightedge; commonly ~3mm maximum | Grind high spots; fill low spots with a compatible levelling compound |
| Moisture | Readings against the adhesive/barrier maker's test method and limit | Wait, dry, or use a suitable barrier system |
| Surface strength | Dusty, crumbly or weak surface (laitance) | Grind or prepare as the adhesive maker specifies |
| Contamination | Curing compounds, paint, old adhesive, oil, sealers | Mechanically remove |
| Cracks and joints | Moving cracks, control joints | Treat per adhesive maker; don't bridge structural movement joints |
| Services | In-slab heating, pipes, conduits | Map before grinding or fixing |
Flatness is checked with a straightedge in several directions across the room. Parquet blocks are short, so they follow small undulations in the slab that long boards might bridge – a flat slab is what makes the finished floor look flat.
Step 2: Test slab moisture properly
Test slab moisture with the method and limit the adhesive or moisture-barrier manufacturer specifies. Surface-dry concrete can still contain a lot of water deeper down, especially on new or ground-bearing slabs.
- New slabs take a long time to dry. In New Zealand, a 100mm slab can take four months or more (PlaceMakers), and drying is slower in cool, humid or unventilated conditions.
- Benchmarks: New Zealand BRANZ guidance uses 75% relative humidity at the slab surface for solid timber strip flooring (BRANZ BU644). In Australia, follow the adhesive or barrier maker's limit for its system.
- Record results – location, method, readings, date and conditions – in the job file.
See moisture content in timber flooring for the timber side of the equation, and our NZ slab guide for BRANZ detail.
Step 3: Choose the barrier and adhesive system
Use one manufacturer's compatible system: primer or barrier, adhesive and any levelling compound. Common options are:
- Moisture-barrier adhesive – a single adhesive formulated to bond the timber and act as a barrier, within stated slab moisture limits.
- Separate liquid-applied barrier (often an epoxy or similar) plus a compatible flooring adhesive – used where slab moisture is higher or the adhesive alone isn't rated for it.
Trowel notch, spread rate, open time, cure time and the maximum slab moisture are all product-specific. Read adhesives and moisture barriers before choosing.
Step 4: Acclimatise the parquet
Bring the timber close to the moisture content it will reach in the finished home – within about ±2% – before laying. Australian interiors typically sit at about 8–14% equilibrium moisture content depending on climate and season (WoodSolutions). Keep boxes sealed until the building is enclosed, wet trades are finished and conditions are close to normal living conditions, then measure the blocks. Details in acclimatising oak flooring.
Step 5: Set out and lay
Set out from a centre line along the main view of the room, then glue blocks outward from the centre.
- Snap the centre line and a perpendicular reference line; confirm square.
- Dry-lay a few rows to confirm row width and how the pattern meets walls and doorways.
- Spread adhesive with the specified trowel over an area you can cover within the adhesive's open time.
- Lay the first rows precisely, interlocking left- and right-hand blocks; tap joints tight.
- Check that blocks are fully bedded – lift one occasionally to inspect adhesive transfer.
- Clean adhesive off the face immediately with the cleaner the adhesive maker recommends.
- Cut in at the perimeter or to a border, leaving the expansion allowance the installation guidance requires – see expansion gaps for solid parquet.
For herringbone setout and waste, see the herringbone layout and waste guide.
Step 6: Cure, sand and finish
Let the adhesive cure as specified, then sand and finish raw blocks. Don't load, sand or roll heavy equipment over the floor until the adhesive data sheet allows it. Whether a Timbo batch is supplied raw or pre-finished: ask Timbo. Finishing options are covered in oil vs polyurethane.
Who is responsible for what
A glued timber floor on a slab involves several parties – agreeing who does what before the job starts avoids disputes later.
| Party | Typical responsibility |
|---|---|
| Builder / owner | Programme slab drying time; enclose and condition the building; finish wet trades; provide services drawings |
| Flooring installer | Test slab and timber moisture; check flatness; prepare the slab; select and apply a compatible adhesive system; record results |
| Adhesive / barrier manufacturer | Publish moisture limits, test methods, trowel, open and cure times; technical support |
| Finish manufacturer | Publish sanding, coating and cure instructions |
| Supplier (e.g. Timbo) | Supply the specified product; answer product questions; handle defect claims under the partner terms |
Write the agreed responsibilities, test results and products used into the job file. For homeowners, the Timbo partner who quotes the job is the person to ask how each of these steps will be handled.
Common mistakes on slabs
| Mistake | Result |
|---|---|
| Laying on a new slab without testing | Cupping, lifting or bond failure |
| Mixing products from different adhesive systems | Poor adhesion; possible loss of manufacturer support |
| Skipping grinding on a slab with curing compound | Adhesive bonds to the compound, not the slab |
| Opening boxes in a damp, unfinished building | Blocks swell, then shrink after handover |
| Tight perimeter with no expansion allowance | Blocks push against walls and lift |
Sources
- Bowens – Hardwood timber flooring
- BRANZ BU644 – Solid timber strip flooring on a concrete slab
- PlaceMakers – Live and let dry
- WoodSolutions – Moisture guide
Frequently asked questions
Can solid parquet be floated over a slab instead of glued?
Solid parquet blocks are generally glued down. Small blocks rely on the adhesive bond to the subfloor to stay flat and tight; floating systems are designed for click-together engineered or laminate boards, not solid parquet.
Who decides whether a slab is dry enough for parquet?
The test results do, measured against the adhesive or moisture-barrier manufacturer's method and maximum reading for its product – those limits govern. The installer normally tests before laying. In New Zealand, BRANZ guidance uses 75% relative humidity at the slab surface as a benchmark.
What if my slab isn't flat enough?
High spots are ground down and low spots filled with a levelling compound compatible with the adhesive system. Australian practice commonly aims for about 3mm under a 3m straightedge; check the adhesive maker's requirements too.
Can parquet go over old tiles or vinyl on a slab?
Sometimes, but it's a job-by-job decision. The old covering must be sound, well bonded and compatible with the adhesive, and the extra height must work at doors. Most installers prefer to remove old coverings and prepare the bare slab. The adhesive maker has the final say.
Do I need a moisture barrier on a new slab?
It is common practice in Australia to use a moisture barrier or a moisture-barrier adhesive under glued timber floors on slabs, especially ground-floor slabs. Whether one is required, and which, depends on the slab test results and the adhesive manufacturer's system.
How long after laying parquet can it be sanded?
Only once the adhesive has cured enough for sanding. Cure time depends on the adhesive, temperature and humidity, so follow the adhesive manufacturer's data sheet.