That hollow, clunky sound underfoot when you walk across a floating floor is one of the most common complaints from NZ homeowners. The good news is that it's usually fixable — and in many cases, you can tackle it yourself. Understanding why it happens is the first step to sorting it out.
Why Does a Floating Floor Sound Hollow?
A floating floor — whether it's laminate, engineered timber, or luxury vinyl plank (LVP) — isn't glued or nailed to the subfloor. Instead, it sits on top, held together by click-lock or tongue-and-groove joints. This design means any gap between the flooring and the subfloor creates an air pocket, and air pockets amplify sound. The main culprits are:
- An uneven subfloor — high or low spots cause the planks to flex and drum
- Insufficient or missing underlay — underlay cushions the floor and absorbs sound
- Moisture-related movement — swelling or cupping from humidity can lift planks
- Inadequate expansion gaps — if the floor has no room to breathe, it can buckle in the middle
- Debris under the floor — grit or offcuts left during installation create hard points
Check the Subfloor First
Before pulling anything up, do a quick assessment. Walk the floor slowly and mark hollow spots with painter's tape. Then check whether the hollow areas correspond to:
- Joins between sheets of particleboard or plywood — these can dip over time
- Areas near exterior walls — more prone to moisture movement in NZ's variable climate
- High-traffic paths — repeated flex wears down underlay faster
If you can access the subfloor from below (e.g., a suspended timber floor with a crawl space), shine a torch up and look for gaps, sagging noggings, or signs of moisture damage.
Fixing a Hollow Floor: Your DIY Options
Option 1: Inject Construction Adhesive
For small, localised hollow spots — especially on a concrete slab subfloor — you can inject low-expansion construction adhesive through the floor without lifting it. Here's how:
- Locate the hollow spot precisely by tapping.
- Drill a small hole (typically 3–4 mm) through the plank at the join or in a low-visibility spot.
- Insert the nozzle of a flexible-tip adhesive syringe and inject a small amount of adhesive.
- Weigh the area down with heavy books or a concrete block for the cure time specified on the product.
- Fill the drill hole with a colour-matched wood filler.
This works best on laminate and engineered timber floors. It's a common trade trick and can be very effective when the hollow area is small.
Option 2: Lift and Re-lay the Affected Section
If the hollow area is large, or if the underlay is clearly worn out or missing, you may need to lift the planks back to that section and start again. Floating floors are designed to be disassembled, so this is more achievable than it sounds:
- Remove the skirting boards or scotia along the nearest wall.
- Carefully unclick the planks row by row until you reach the problem area.
- Inspect and repair the subfloor — fill low spots with a floor-levelling compound (products from Ardex or Mapei are widely used in NZ).
- Replace damaged or compressed underlay with a quality acoustic underlay.
- Re-lay the planks, ensuring correct expansion gaps (typically 10–12 mm from walls).
Option 3: Improve the Underlay
If you're re-laying anyway, upgrading your underlay makes a significant difference. Look for underlay with a good Impact Sound Insulation (IIC) rating. Options available at Bunnings and Mitre 10 include foam, cork, and combination foam/foil products. Cork underlay is particularly good for acoustic performance and is a popular choice in NZ homes.
Addressing Moisture — A Key NZ Consideration
New Zealand's climate — especially in regions like Auckland, Northland, and the West Coast — means moisture is often a hidden villain. Before re-laying, check:
- Concrete slabs: Test for moisture vapour transmission. Most floating floor manufacturers require a moisture barrier if readings are above their specified threshold.
- Timber subfloors: Look for any signs of rot, mould, or excessive movement. BRANZ has excellent guidance on subfloor moisture management.
- Healthy Homes compliance: If you're a landlord, note that the Healthy Homes Standards require adequate underfloor insulation and ground moisture barriers in rental properties.
Preventing the Problem Next Time
| Prevention Step | Why It Matters |
|---|---|
| Flatten the subfloor to within 3 mm over 1.8 m | Eliminates flex points and air pockets |
| Use quality acoustic underlay | Reduces hollow sound and impact noise |
| Leave correct expansion gaps | Prevents buckling that lifts planks |
| Acclimatise flooring before install | Reduces post-install movement |
| Install a moisture barrier on concrete | Stops vapour causing swelling |
When to Call a Professional
Some hollow floor situations go beyond a straightforward DIY fix. Call a qualified flooring installer if:
- The hollow area covers a large portion of the floor
- You suspect significant subfloor damage, rot, or structural movement
- The floor has buckled or planks have separated at the joins
- Moisture is clearly the cause and you're unsure of the source
- The floor is under warranty — DIY repairs may void manufacturer cover
A professional flooring installer can assess the subfloor properly, use commercial-grade levelling compounds, and re-lay the floor to manufacturer specifications. You can find qualified local flooring installers on tradedirectory.co.nz.
Note: Floating floor installation and repair is not restricted work under NZ law, so homeowners can legally do it themselves. However, if your investigation uncovers plumbing leaks or electrical cables near the subfloor, stop work and contact a licensed plumber (PGDB) or electrician (EWRB) before continuing.