Subfloor preparation is arguably the most critical phase of any flooring installation. A well-prepared subfloor ensures your hybrid flooring installs smoothly, performs optimally, and lasts for its full expected lifespan. Conversely, inadequate preparation leads to problems ranging from annoying squeaks and uneven surfaces to premature wear and void warranties. This guide covers preparation requirements for the most common subfloor types found in Australian homes.
Understanding Subfloor Requirements
Regardless of subfloor type, three fundamental requirements must be met before installing hybrid flooring: the surface must be level, clean, and dry. Failing to meet any of these requirements can cause immediate installation problems or long-term performance issues.
Levelness Standards
The industry standard for subfloor flatness specifies a maximum deviation of 3mm over any 3-metre span. This tolerance accounts for the rigidity of hybrid flooring planks and the capabilities of click-lock joining systems. Deviations beyond this threshold can prevent planks from clicking together properly, create visible high or low spots, and cause planks to rock underfoot.
Testing Levelness
Use a 2-metre straightedge or level, moving it across the floor in multiple directions. Slide a 3mm spacer under the straightedge at any point, if the spacer slides freely underneath, that area needs attention.
Cleanliness Standards
The subfloor must be free of all debris, dust, paint drips, adhesive residue, and any other material that could create bumps under the underlay. Even small particles can telegraph through thin underlay and create noticeable imperfections in the finished floor. Additionally, debris can interfere with the click-lock mechanism during installation.
Moisture Requirements
Excessive subfloor moisture is one of the most common causes of flooring failure. While hybrid flooring cores are waterproof, moisture trapped beneath the floor can create mould, degrade adhesives, and cause long-term problems. Different subfloor types have different moisture testing requirements and acceptable limits.
Preparing Concrete Subfloors
Concrete is one of the most common subfloors in Australian homes, particularly in newer construction and ground-floor applications. Concrete preparation requires attention to curing, levelness, and moisture content.
New Concrete Requirements
New concrete must be fully cured before flooring installation. The general rule is one month of curing time per 25mm of slab thickness, though this varies with environmental conditions. A 100mm slab typically requires at least four months to cure adequately. Installing flooring over insufficiently cured concrete traps moisture, leading to potential mould growth and adhesive failure.
Moisture Testing
All concrete subfloors should be tested for moisture before installation, even in older homes. The simplest test method involves taping a 1-metre square of plastic sheeting to the floor for 24-48 hours. If condensation appears on the underside of the plastic or the concrete appears darker, moisture levels are too high.
For more accurate results, use a pin-type moisture meter (readings should be below 4%) or have a professional conduct a calcium chloride test (acceptable levels below 3 pounds per 1,000 square feet per 24 hours). If moisture levels exceed acceptable limits, install an appropriate vapour barrier before proceeding.
Levelling Concrete
Address low spots with self-levelling compound, available at most hardware stores. Clean and prime the area first, then pour the compound according to manufacturer instructions. It seeks its own level and cures within 24-48 hours. For high spots, use a concrete grinder to remove material until level with surrounding areas.
Important
Never install hybrid flooring directly over painted concrete without proper testing. Old paint may not provide adequate adhesion for underlays, and some paints act as vapour barriers trapping moisture beneath.
Preparing Timber Subfloors
Timber subfloors are common in older Australian homes and upper levels of multi-storey construction. Preparation focuses on structural stability and surface condition.
Assessing Structural Condition
Walk the entire subfloor, noting any areas with excessive bounce, squeaks, or soft spots. Squeaky boards typically indicate loose fixings, while soft spots may suggest damaged or deteriorated timber. All structural issues must be addressed before installation.
Secure loose boards with additional screws, using screws long enough to penetrate at least 25mm into the underlying joists. For persistent squeaks, apply construction adhesive between boards and joists where accessible from below.
Surface Preparation
Timber subfloors must be flat as well as structurally sound. Check for cupped or crowned boards, protruding nail heads, and significant gaps between boards. Belt sand excessively cupped or uneven areas. Punch down any raised nail or screw heads below the surface level. Fill large gaps with flexible timber filler to prevent underlay from sagging into voids.
Moisture Considerations
While timber subfloors don't require the same moisture testing as concrete, ensure adequate ventilation beneath floor-level timber subfloors. Check that subfloor vents are clear and functional. In humid climates or for floors over poorly ventilated crawl spaces, consider installing a moisture barrier.
Installing Over Existing Flooring
Hybrid flooring can often be installed over existing hard flooring, saving the cost and effort of removal. However, specific preparation is required for different existing floor types.
Over Tiles
Tiles provide an excellent base for hybrid flooring installation, provided they're firmly adhered and level. Check for any loose or hollow-sounding tiles by tapping, and secure or remove any that aren't solidly bonded. Fill grout lines if they exceed 3mm depth with appropriate filler to prevent underlay compression over time.
Over Vinyl
Sheet vinyl or vinyl tiles can remain in place if they're well-adhered and in good condition. Remove any lifting edges and fill any damage. For cushioned vinyl with significant padding, consider removal as the compression under hybrid flooring can cause issues with the click-lock system.
Over Carpet
Never install hybrid flooring over existing carpet. Carpet must be completely removed, including all underlay and any remaining adhesive or staples. Vacuum thoroughly after removal to eliminate all dust and debris.
Installing Underlay and Vapour Barriers
If your hybrid flooring doesn't include attached underlay, selecting and installing appropriate underlay is part of subfloor preparation.
Underlay Types
Standard foam underlay (2-3mm) provides basic cushioning and minor sound absorption. Acoustic underlay (3-5mm) significantly reduces impact sound transmission, ideal for upper floors. Cork underlay offers excellent thermal and acoustic properties but at higher cost.
Installation Process
Roll out underlay perpendicular to the direction your planks will run. Butt edges together without overlapping, and tape all seams with underlay tape. On concrete requiring a vapour barrier, either install the barrier first and underlay second, or choose underlay with an integrated vapour barrier.
For comprehensive installation guidance, see our DIY installation tips guide. If you're installing in wet areas, review our specific guidance on wet area installation.