Crumbled or missing grout between floor tiles is a very common problem in NZ homes, and the good news is that regrouting is a straightforward DIY job in most cases. As long as the tiles themselves are still firmly bonded to the substrate and there are no signs of water damage or movement underneath, you can regrout the affected joints yourself over a weekend.
Why Does Grout Crumble?
Grout can deteriorate for several reasons:
- Age and wear – standard cement-based grout has a finite lifespan, especially in high-traffic areas.
- Incorrect mixing or application – grout that was too wet when applied or not properly cured will be weak.
- Movement in the substrate – slight flexing in timber floors can crack and dislodge grout over time.
- Moisture ingress – particularly in bathrooms and kitchens, water can undermine grout if the waterproofing membrane beneath has failed.
- Wrong grout type – using wall grout on floors, or unsanded grout in wide joints, leads to premature failure.
Before you start repairs, check whether the tiles themselves are loose or hollow-sounding when tapped. If they are, the problem is deeper than the grout and you should consult a qualified tiler.
Tools and Materials You'll Need
- Grout rake or oscillating multi-tool with a grout-removal blade
- Stiff brush and vacuum
- Bucket and mixing paddle (or a margin trowel for small batches)
- Grout float (rubber-faced)
- Sponge and clean water
- Safety glasses and dust mask
- Appropriate grout (see below)
- Grout sealer (for cement-based grout)
Choosing the Right Grout
Matching the correct grout type to your situation is critical:
| Grout Type | Best For | Joint Width |
|---|---|---|
| Unsanded cement grout | Wall tiles, narrow joints | Under 3 mm |
| Sanded cement grout | Floor tiles, wider joints | 3 mm – 12 mm |
| Epoxy grout | Wet areas, commercial, stain-prone | Any width |
| Premixed acrylic grout | Light-duty repairs | Narrow joints only |
For most NZ floor tile repairs, a sanded cement-based grout is the standard choice. Epoxy grout is more durable and water-resistant — ideal for shower floors or areas prone to staining — but it is harder to work with and sets quickly, so beginners should practise first.
You can find a good range of grouts at Bunnings, Mitre 10, and PlaceMakers. Specialist tile adhesive and grout brands such as Ardex and Mapei are widely available through tile shops and trade suppliers and are well regarded by NZ tilers.
Step-by-Step Regrouting Process
1. Remove the Old Grout
Using a grout rake or an oscillating multi-tool fitted with a grout blade, carefully rake out the crumbled and loose grout to a depth of at least 5–6 mm. Take care not to chip the tile edges. Wear safety glasses — grout dust and fragments can fly. Vacuum out the joints thoroughly, then brush away any remaining dust.
2. Clean the Joints
Wipe the joints with a damp sponge to remove fine dust. Allow to dry completely before grouting — damp joints can weaken the new grout.
3. Mix the Grout
Follow the manufacturer's instructions precisely. Mix to a smooth, peanut-butter-like consistency with no lumps. Avoid adding extra water — this is one of the most common mistakes and leads to weak, crumbly grout (the same problem you're fixing!).
4. Apply the Grout
Using a rubber grout float held at roughly 45 degrees, press the grout firmly into the joints, working diagonally across the tile faces to pack the joints fully. Work in manageable sections of about 1–2 square metres at a time.
5. Clean Off the Excess
Once the grout has started to firm up (check the manufacturer's open time — usually 15–30 minutes), use a damp sponge wrung out well to wipe diagonally across the tiles, removing surface grout without pulling it from the joints. Rinse the sponge frequently. Repeat until the tile faces are clean.
6. Final Polish and Cure
Once the grout has hazed over (usually within an hour), buff the tiles with a dry cloth. Keep foot traffic off the floor for at least 24 hours, and avoid wetting the area for 48–72 hours, or as directed on the packaging.
7. Seal the Grout
Once fully cured (typically 7 days for cement-based grout), apply a penetrating grout sealer to protect against moisture and staining. This is especially important in NZ bathrooms and kitchens. Reapply sealer every 1–2 years depending on wear.
Movement Joints and Silicone
If grout keeps cracking in the same spot — particularly at corners, along skirting boards, or where tiles meet a different surface — this is likely a movement joint that should be filled with flexible silicone sealant, not rigid grout. Sika and other brands make tile-grade silicone in a range of colours. Using grout in a movement joint will just result in the same cracking recurring.
Wet Area and Waterproofing Considerations
In bathrooms and other wet areas, the NZ Building Code (specifically Clause E3 – Internal Moisture) requires adequate waterproofing beneath tiled surfaces. If you notice crumbling grout accompanied by soft or hollow tiles, discolouration, or musty smells, the waterproofing membrane may have been compromised. In this case, regrouting alone won't solve the problem — the tiles may need to come up and the membrane repaired or replaced. Check MBIE Building Performance for guidance on wet area requirements.
When to Call a Professional
Consider calling a qualified tiler if:
- Multiple tiles are loose, hollow, or cracked
- You suspect the waterproofing membrane has failed
- The subfloor feels soft or shows signs of water damage
- The grout keeps failing in the same area (possible structural movement)
- You're dealing with large areas or a complex pattern
- You want a colour-matched or epoxy grout finish and lack experience
A skilled tiler will diagnose the root cause rather than just patch the surface. You can find experienced local tilers on tradedirectory.co.nz.
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