Yes, you can absolutely install timber flooring on a concrete slab. For a successful installation, the concrete must be perfectly level, structurally sound, and critically, completely dry. The success or failure of your floor comes down to the concrete’s moisture content and choosing the correct installation method such as direct stick, floating, or laying over a plywood subfloor. If a concrete slab fails a moisture test or lacks a proper moisture barrier, the timber will absorb that moisture, leading to cupping, buckling, and expensive floor failures.
| Installation Method | Best Suited For | Slab Preparation Required | Relative Cost |
| Direct Stick (Glue Down) | Engineered timber, premium feel, underfloor heating | High (Perfectly flat & dry slab required) | Medium to High |
| Over Plywood | Solid timber on concrete, superior moisture protection | Medium (Ply acts as a buffer) | High (Requires extra materials & labour) |
| Floating Floor | Engineered timber, apartments with acoustic needs | Low to Medium (Underlay used) | Low |
| Over Battens | Matching existing floor heights, adding heavy insulation | Medium | High |
Can You Install Timber Flooring Directly on Concrete?
Yes. Laying a timber floor on concrete is one of the most common installation scenarios for modern homes and extensions in Melbourne. However, you cannot simply drop raw timber onto bare concrete without assessing the environment first.
Generally, there are three primary ways to achieve this:
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Direct Stick: Gluing the floorboards directly to the concrete surface using a specialised polymer adhesive.
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Over Plywood: Mechanically fixing or gluing a plywood layer to the slab (over a plastic vapour barrier), and then installing the timber over the ply.
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Floating Floor: Clicking or gluing the boards together over a foam acoustic/moisture underlay, without physically attaching them to the slab.
Solid vs Engineered Timber on Concrete
Choosing between solid timber and engineered timber drastically impacts how your floor will be installed over a concrete slab.
Engineered timber on concrete is the most popular choice for modern Melbourne homes. Because engineered boards are constructed with cross-directional layers of plywood or HDF beneath a real hardwood veneer, they are highly dimensionally stable. They resist the natural expansion and contraction caused by Melbourne’s fluctuating humidity. This stability makes engineered timber the perfect candidate for direct stick timber flooring or floating installations.
Solid timber on concrete, while offering incredible longevity and traditional appeal, is far more susceptible to moisture variations. Solid timber boards want to breathe, expand, and contract. Therefore, laying solid timber directly onto a concrete slab requires a flawless moisture barrier and premium adhesives. More often, installers prefer laying solid timber over a plywood subfloor to provide a secure nailing base and an extra buffer against slab moisture.
Solid vs Engineered Timber on Concrete: Comparison
| Feature | Solid Timber | Engineered Timber |
| Dimensional Stability | Low to Medium (expands/contracts more) | High (cross-laminated core resists movement) |
| Best Install Method on Slab | Over Plywood, Direct Stick (with extreme care) | Direct Stick, Floating |
| Moisture Sensitivity | Very High | Moderate |
| Refinishing | Can be sanded and polished multiple times | Can be sanded 1–3 times depending on veneer thickness |
| Cost | Generally Higher (Materials + Labour) | Moderate to High |
Installation Methods Compared
When evaluating how to install hardwood flooring on a concrete slab, your installer will recommend one of four methods based on your site conditions, budget, and chosen timber.
Direct Stick (Glue Down)
Direct stick timber flooring involves trowelling a full bed of flexible polyurethane or MS polymer adhesive directly onto the prepared concrete slab, then laying the boards into the glue.
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Best For: Engineered timber and premium residential builds.
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Pros: Creates a solid, premium feel underfoot with zero “hollow” acoustic bounce. It allows the floor to expand and contract naturally as a single unified layer.
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Cons: Demands meticulous slab preparation. The concrete must be exceptionally flat and completely free of contaminants. It is also harder and more expensive to remove in the future.
Over Plywood with a Polyethylene Vapour Barrier
This method involves laying a heavy-duty builder’s plastic (polyethylene vapour barrier) over the bare concrete. Sheets of plywood (typically 12mm or 15mm) are then fastened through the plastic and into the slab using masonry anchors or shot-fired pins. The timber floor is then glued and secret-nailed to the plywood.
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Best For: Traditional solid timber on concrete and uneven slabs.
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Pros: Outstanding moisture protection. The plywood provides a perfect, flat subfloor that mimics traditional timber joists.
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Cons: Raises the overall floor height by 25mm to 35mm (timber + ply), which may require adjusting doors and skirting boards. Higher material and labour costs.
Floating Floor
A floating timber floor on concrete is not physically attached to the slab. Instead, an underlay (incorporating a moisture barrier and acoustic foam) is rolled out. The engineered timber boards are then clicked or edge-glued together, resting on top of the underlay.
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Best For: Budget-conscious projects, apartments requiring acoustic ratings, and DIY installations.
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Pros: Fast installation, lower labour costs, and very forgiving of minor slab imperfections.
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Cons: Can produce a slightly hollow sound when walked upon. Limited to engineered or laminate products; you cannot float a solid timber floor.
Over Battens
Timber battens are fixed to the concrete slab, and the floorboards are nailed to the battens.
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Best For: Correcting severe height discrepancies or when heavy sub-floor insulation/cabling is required.
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Pros: Allows space for services and heavy insulation beneath the floor.
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Cons: Rarely used in standard modern builds due to the massive floor height increase (often 50mm+).
Concrete Slab Moisture Testing
The single most common cause of timber floor failure in Melbourne is concrete moisture. Concrete is porous and acts like a rigid sponge. Even if a slab looks and feels dry to the touch, it can hold massive amounts of water internally.
Before any timber flooring installation Melbourne professionals undertake, thorough concrete moisture testing is mandatory.
The industry standard, guided by the Australasian Timber Flooring Association (ATFA) and major manufacturers, dictates that for a direct stick application, the concrete moisture content must not exceed 5.5% when tested with an approved concrete moisture meter. Some premium manufacturers, like Woodcut, specify a strict 6% maximum on a moisture encounter meter, alongside an in-slab Relative Humidity (RH) reading of no more than 80%.
The In-Slab RH Test (Hygrometer):
While surface moisture meters are helpful, the most accurate method is an in-slab RH test. This involves drilling small holes into the concrete, inserting a hygrometer probe, and sealing it to measure the moisture vapor inside the slab itself. A professional installer will take at least 3 to 4 readings per distinct living area to ensure consistency.
Cure Time:
A common misconception is that a slab is dry once it is hard. In reality, a new concrete slab requires approximately 1 month of drying time per 25mm of thickness. Most flooring manufacturers stipulate that a new slab must be at least 60 days old before even attempting a moisture test.
Why Melbourne Slabs Vary:
Melbourne’s unique geography and property styles create specific moisture challenges:
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Reactive Clay Soils: Melbourne’s northern and western suburbs are notorious for reactive clay soils that retain ground moisture, increasing the risk of hydrostatic pressure pushing water up through older ground-floor slabs.
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Older Homes without DPC: Many older homes lack a modern Damp Proof Course (DPC) beneath the slab.
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New Apartments: Rapid construction schedules often mean apartment slabs haven’t fully cured before fit-out, trapping moisture in the concrete.
Moisture Barriers
If a concrete slab tests above the safe moisture limits (but below extreme fail levels), or if the installer is taking preventative measures against seasonal ground moisture, a moisture barrier is required.
Types of Moisture Barriers:
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Liquid Membranes (Polyurethane or Epoxy): These are roll-on coatings applied directly to the concrete. They penetrate the porous surface and cure into a hard, waterproof seal. They are standard practice for direct stick timber flooring on concrete.
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Polyethylene Plastic Sheet (Builder’s Plastic): Typically a 200um plastic sheet overlapped and taped at the seams. This is used exclusively for floating floors and plywood subfloor systems.
A crucial warning: A moisture barrier timber flooring system manages standard vapor transmission. It does not fix a wet slab. If your slab has an active water leak, poor external drainage, or severe rising damp, no roll-on barrier will stop the eventual hydrostatic pressure from lifting your floor.
Slab Preparation and Levelness
A timber floor is only as flat as the concrete beneath it.
Flatness Tolerance:
Industry standards require the concrete to be flat to within 3 mm over a 3 m straight edge. If the concrete dips or peaks beyond this tolerance, the timber boards will bounce, squeak, or fail to adhere.
Preparation Steps:
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Grinding High Spots: Concrete grinders fitted with diamond blades are used to shave down peaks and ridges in the slab.
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Self-Levelling Compound: Low spots, trenches, or aggressively sloped areas are filled with a cementitious self-levelling compound timber floor prep product. This liquid is poured onto the low spots and cures to a perfectly flat finish.
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Removing Contaminants: Adhesives cannot bond to paint, plaster overspray, old vinyl glue, wax, or oil. The slab must be mechanically ground back to bare, porous concrete before any glue or moisture barrier is applied.
Acclimatisation, Adhesive and Expansion Gaps
Once the slab is flat and dry, the timber itself must be prepared for the environment.
Acclimatisation:
Never install timber straight off the delivery truck. The boards must be stored inside the installation environment for several days to acclimatise to the room’s normal temperature and humidity levels. If installed completely cold or damp, the boards will drastically change size once the home’s heating or cooling is turned on.
Adhesives:
For direct stick installations, highly flexible MS polymer or polyurethane adhesives are standard. These glues cure to a tough, rubbery consistency, allowing the timber to expand and contract microscopically without snapping the glue bond. The adhesive must be applied with a 6 mm V-notch trowel to ensure full coverage and proper ridge height.
Expansion Gaps:
Wood expands across its width when humidity rises. If the floor is locked tight against a wall, it has nowhere to go but up (buckling). ATFA standards dictate a minimum expansion gap of 10 mm to 12 mm around the entire perimeter of the floor, as well as against all fixed vertical obstacles (kitchen cabinets, pipes). Always follow the manufacturer’s specific guidelines, as some wider boards require even larger gaps. These gaps are later covered by skirting boards or scotia trims.
Underfloor Heating and Apartments
Installing a timber floor over concrete with in-slab heating requires specific considerations. Engineered timber is vastly superior for this application. A direct stick engineered floor is highly recommended over hydronic in-slab heating, as the direct glue bond transfers heat efficiently without trapping an insulating layer of air (which can happen with floating floors).
For those living in multi-story buildings, acoustic regulations come into play. To meet strata Body Corporate requirements, you will likely need to install an acoustic underlay. You can read more about acoustic requirements and building codes in our dedicated timber flooring apartment guide.
Timber Floor on Concrete Cost in Melbourne
When budgeting for your project, separate the cost of the timber from the cost of the installation and slab preparation.
For a standard direct stick installation in Melbourne, labour alone typically ranges from $55 to $60 per square metre. However, this is just the baseline for laying the floor.
Your final installation cost will be influenced by several factors:
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Moisture Barriers: Applying a roll-on epoxy or PU moisture barrier usually adds $15 to $25 per square metre.
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Slab Levelling: Concrete grinding and pouring self-levelling compound are usually charged at an hourly or daily rate, plus materials. Never skip this step to save money; it will ruin the floor.
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Installation Method: Floating a floor is cheaper than gluing it. Laying plywood first is the most expensive route.
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Patterns: Laying timber in a herringbone or chevron pattern requires intense precision and double the labour time, adding a significant surcharge.
Always request a comprehensive site inspection to get an accurate quote, rather than relying on a fixed “per square metre” guess over the phone. (For more details, see our installation cost guide).
Common Problems: Cupping, Buckling, Popping
If slab preparation and moisture testing are skipped, the results are visually devastating and costly to repair. According to building science research (such as BRANZ BU644), timber constantly seeks equilibrium with its environment.
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Cupping: The edges of the board rise higher than the centre. This happens when the bottom of the board absorbs moisture from a damp concrete slab, causing the underside to expand faster than the top.
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Buckling / Tenting: The floor literally lifts off the concrete in a tent shape. This is caused by severe moisture expansion combined with a lack of perimeter expansion gaps. The wood expands, hits the walls, and pushes upward.
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Popping / Hollow Spots: When walking across the floor, you hear a sticky popping sound or a hollow clack. This indicates the slab was not level, or inadequate glue was used, meaning the timber has not bonded to the concrete.
Expert Installation Starts from the Ground Up
Installing a stunning timber floor on a concrete slab requires more than just high-quality boards; it demands scientific moisture testing, meticulous concrete preparation, and expert craftsmanship. If you are renovating a ground-floor home, building a new extension, or updating a Melbourne apartment, Boss Timber Flooring is here to ensure your investment is installed to last a lifetime.
Contact Boss Timber Flooring today for an expert site inspection and a transparent, comprehensive quote tailored to your specific slab conditions.
FAQ
Can you lay timber floors directly on concrete?
Yes, you can lay timber directly on concrete using the direct stick (glue-down) method. The concrete must be structurally sound, perfectly flat (3mm tolerance over 3m), and test below 5.5% moisture content. Engineered timber is highly recommended for direct concrete installation.
Do I need a moisture barrier for timber flooring on concrete?
Yes, in most cases. Concrete is porous and absorbs ground moisture. Applying a liquid polyurethane moisture barrier (for glue-down) or a plastic sheet (for floating floors) protects the timber from sub-slab moisture, preventing cupping and buckling.
Is it better to float or glue down timber on concrete?
Gluing down (direct stick) offers a premium, solid feel underfoot without the hollow sound associated with floating floors. However, floating is cheaper, faster, and better suited for apartments where specific acoustic underlays are required by building management.
How dry must a concrete slab be for timber flooring?
Industry standards typically require a concrete slab to have a moisture content of 5.5% or lower when tested with a surface moisture meter. For in-slab relative humidity (RH) testing, it should generally not exceed 80%.
Can solid timber go on a concrete slab?
Yes, but it requires extreme caution. Solid timber is highly susceptible to moisture changes. It is usually recommended to install a heavy-duty moisture barrier, fix a plywood subfloor to the concrete, and then nail and glue the solid timber to the plywood.
