How to Fix a Hollow-Sounding Tile Without Retiling Everything

A hollow-sounding tile — that tell-tale "clunk" when you tap it — means the tile has debonded from the substrate beneath it. The good news is that in many cases you can fix one or two hollow tiles without ripping out the whole floor or wall. The approach depends on whether the tile is still intact, how many are affected, and what caused the problem in the first place.

Why Do Tiles Go Hollow?

Before you fix anything, it pays to understand the cause. Common reasons include:

• Insufficient adhesive coverage during original installation (NZS 3604 and good trade practice call for full-bed coverage, especially in wet areas)
• Movement in the substrate — particularly in timber-framed NZ homes where floors flex seasonally
• Moisture ingress behind wall tiles, which can break down adhesive bonds over time
• Using the wrong adhesive for the tile type or location (large-format tiles and natural stone need flexible adhesives)
• Thermal expansion in outdoor or unheated areas

Tapping around the affected tile will help you map out how many tiles are hollow. If it's just one or two isolated tiles, a targeted repair is very achievable. If large sections sound hollow, or if you notice cracking grout lines, lippage, or rising damp, the problem is likely structural and you should get a professional assessment.

Option 1 — Grout Injection (Least Invasive)

Grout or adhesive injection is the least disruptive method and works best when the tile is still firmly in place with no cracks, and there is a small void beneath it.

What you need

• A rotary tool or grout saw
• Low-viscosity epoxy injection adhesive (products from Sika or Ardex are well regarded in NZ)
• Injection syringe or nozzle
• Matching grout

Steps

1. Remove grout from one or two joints around the hollow tile using a grout saw or oscillating tool. Take care not to chip the tile edge.
2. Inject low-viscosity adhesive into the void through the open joint. Work slowly and allow the adhesive to flow under the tile. Some tilers drill a small hole through the grout joint rather than removing grout entirely.
3. Apply gentle pressure — place a weighted flat board over the tile while the adhesive cures. Follow the manufacturer's cure time (typically 24 hours).
4. Re-grout the joints with matching grout. Getting a colour match can be tricky on older tiles, so buy a small sample pot first.

This method won't work if the void is large, if the tile is cracked, or if there's active moisture behind the tile.

Option 2 — Remove, Re-Bond, and Replace

If the tile is cracked or the void is too large for injection, you'll need to carefully remove and re-lay the tile.

Removing the tile without breaking it

1. Score and remove all surrounding grout with a grout saw.
2. Use an oscillating multi-tool with a thin blade to cut through the adhesive bed around the perimeter.
3. Gently insert a wide, flat chisel and work around the tile — patience here saves the tile.
4. If the tile breaks, keep the pieces as a template to source a replacement.

Re-bonding

1. Scrape the substrate clean — remove all old adhesive so you have a flat, sound surface.
2. Choose the correct adhesive for your situation. For wet areas (bathrooms, showers), use a flexible, waterproof adhesive that meets the requirements of NZ Building Code clause E3. Products like those in the Ardex or Mapei (Mapei NZ) ranges are commonly used by NZ tilers.
3. Apply adhesive using the back-buttering method — spread adhesive on both the substrate and the back of the tile for full coverage.
4. Press firmly, check for level, and allow to cure before grouting.

Matching Grout and Tiles

One of the trickiest parts of a spot repair is matching existing grout colour and tile appearance. Take a photo and a small grout sample to your local tile supplier or a store like Bunnings or Mitre 10. If the tiles are discontinued, check salvage yards or online marketplaces — NZ Facebook groups for building materials can be surprisingly useful.

What About Wet Areas and Waterproofing?

If the hollow tile is in a shower, bathroom floor, or any wet area, be aware that removing tiles may compromise the waterproof membrane beneath. Under the NZ Building Code (clause E3), wet area waterproofing is critical. If you suspect the membrane is damaged, stop and call a licensed tiler or waterproofing specialist before proceeding. Repairing a failed membrane without re-tiling is rarely straightforward. You can find qualified local tilers on tradedirectory.co.nz.

When to Call a Professional

Call a qualified tiler if:

• More than a few tiles are hollow — this suggests a systemic adhesive or substrate failure
• The tiles are in a wet area and you suspect waterproofing damage
• You notice cracking, heaving, or movement in the tile surface
• The substrate is compressed fibre cement or a timber floor that may need reinforcing before re-tiling
• You're unsure of the cause — fixing the symptom without addressing the cause means the problem will return

A professional tiler can also advise whether a building consent is required. Most like-for-like tile repairs fall under Schedule 1 exemptions, but always confirm with your local council if you're unsure.

Sources & Further Reading

• MBIE Building Performance — NZ Building Code
• BRANZ — Tiling and Wet Area Guidance
• Ardex NZ — Tile Adhesives and Grouts
• Mapei NZ — Tile Installation Products
• Sika NZ — Construction Adhesives
• Tenancy Services — Healthy Homes Standards