A hollow sound when you tap a floor tile — sometimes called a "drummy" tile in the trade — means the tile has debonded from the adhesive or substrate beneath it. In many cases this is a straightforward DIY fix, but it pays to understand the cause before you reach for the grout saw.
Why Do Tiles Go Hollow?
Tiles debond for several common reasons:
- Insufficient adhesive coverage during original installation (tile industry guidelines recommend at least 80% bed coverage, more in wet areas)
- Substrate movement — timber subfloors flex, causing the bond to crack over time
- Moisture getting under the tile through failed grout or a cracked tile
- Wrong adhesive used — for example, a wall adhesive used on a floor, or a standard adhesive used in a wet area
- Thermal expansion — common in areas with underfloor heating or large temperature swings
Tapping across the floor with your knuckle or the handle of a screwdriver will reveal the extent of the problem. A dull thud indicates debonding; a solid ring means the tile is still well bonded.
Assess the Damage First
Before doing anything, check:
- Is the tile cracked? A cracked tile will need replacing regardless.
- How many tiles are affected? A single hollow tile is a simple repair. A large area of hollow tiles may point to a systemic problem — substrate failure, ongoing moisture ingress, or a poorly prepared original installation.
- Is it in a wet area? Bathrooms and laundries are subject to the NZ Building Code clause E3 (Internal Moisture). Failed tiles in wet areas can allow water into the structure, so act promptly.
- Is the subfloor timber or concrete? Timber subfloors move more and may need a flexible adhesive or decoupling membrane.
Tools and Materials You'll Need
| Item | Where to find it |
|---|---|
| Grout saw or oscillating multi-tool | Bunnings or Mitre 10 |
| Cold chisel and hammer (or suction cup) | Hardware stores |
| Notched trowel (6 mm or 10 mm) | Hardware stores |
| Flexible floor tile adhesive | PlaceMakers, Bunnings, Mitre 10 |
| Matching grout | Hardware stores or tile specialists |
| Grout float and sponge | Hardware stores |
| Tile spacers | Hardware stores |
For adhesive, look for a polymer-modified, flexible tile adhesive suitable for floors — products from Ardex or Mapei are well regarded in the NZ trade. In wet areas, use a product rated for wet-area floor use and check the manufacturer's datasheet.
Step-by-Step: Re-Bedding a Hollow Tile
1. Remove the Grout
Using a grout saw or oscillating multi-tool, carefully cut out the grout around all four edges of the affected tile. Take your time — you don't want to chip adjacent tiles.
2. Lift the Tile
Slide a stiff putty knife or cold chisel under one corner and gently lever the tile up. If the tile is intact and you want to reuse it, work slowly. A suction cup can help you lift it cleanly once it's free.
3. Clean the Substrate
Scrape off all old adhesive from both the back of the tile and the floor. The substrate must be clean, flat, and dry before re-bedding. Any high spots should be ground back; low spots can be filled with a suitable floor levelling compound.
4. Apply Fresh Adhesive
Using a notched trowel, spread fresh adhesive onto the substrate (and back-butter the tile for better coverage). Press the tile firmly into place, twisting it slightly to collapse the ridges and maximise contact. Use tile spacers to maintain even grout joints.
5. Allow to Cure, Then Re-Grout
Leave the adhesive to cure fully — check the manufacturer's datasheet for the recommended time (typically 24 hours minimum, longer in cool or damp conditions). Then apply matching grout, working it into the joints with a grout float. Clean off excess with a damp sponge before it sets.
6. Seal if Required
In wet areas or where unglazed tiles are used, apply a suitable grout sealer once the grout has fully cured.
What If You Can't Lift the Tile Intact?
If the tile cracks during removal, you'll need a replacement. Take a piece of the broken tile to a tile specialist to try to match it — this can be tricky with older tiles. If an exact match isn't available, consider replacing a larger section or a feature row for a more intentional look.
Preventing the Problem in Future
- Use a flexible, polymer-modified adhesive on timber subfloors
- Ensure full adhesive coverage (back-butter tiles as well as spreading on the floor)
- Keep grout lines sealed, especially in wet areas, to prevent moisture ingress
- Allow adequate expansion joints around the perimeter of large tiled areas
BRANZ publishes good guidance on tile installation best practice for NZ conditions.
When to Call a Professional
Call a qualified tiler or handyman if:
- Multiple tiles across a large area are hollow — this suggests a substrate or installation problem that needs proper diagnosis
- The subfloor feels soft or spongy, which may indicate rot or structural damage (this could require a Licensed Building Practitioner)
- The hollow tiles are in a shower or wet area and you suspect water has been getting into the wall or floor structure — moisture damage can escalate quickly
- You're unsure about matching tiles or achieving a watertight finish in a wet area
A skilled local tiler or handyman can re-bed tiles efficiently and ensure the result is watertight and durable. You can find qualified tradespeople in your area on tradedirectory.co.nz.
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