How to Fix Grout Lines That Have Gone White and Chalky

White, chalky grout lines are a common frustration for NZ homeowners, and the good news is that in most cases you can fix them yourself with a bit of patience and the right products. The cause is usually efflorescence (mineral salts migrating to the surface) or grout that has been damaged by moisture, cleaning products, or poor original installation. Here's how to diagnose the problem and get your grout looking great again.

What Causes Grout to Go White and Chalky?

Before you reach for the grout pen or a bag of new grout, it pays to understand what's going on:

• Efflorescence – Soluble salts from the substrate, adhesive, or water travel through the grout and crystallise on the surface as a white, powdery deposit. This is especially common in wet areas like showers and laundries, and in NZ's more humid regions.
• Grout haze – Residual grout left on the tile surface during installation that wasn't cleaned off properly. It dries to a dull, chalky film.
• Moisture damage – Repeated wetting and drying can break down grout, causing it to lighten, crumble, or powder.
• Harsh cleaners – Acidic or bleach-based cleaners can strip colour and binders from grout over time.
• Poor original mix – Grout that was mixed with too much water or applied incorrectly will be weak and prone to chalking.

Step 1 – Clean and Assess the Grout

Start by giving the grout a thorough clean to see what you're actually dealing with.

1. Mix a solution of warm water and a pH-neutral tile cleaner (available at Bunnings or Mitre 10).
2. Scrub the grout lines with a stiff nylon brush — avoid metal brushes as they can scratch tiles.
3. Rinse well and allow to dry completely (at least 24 hours in a well-ventilated area).

If the white residue disappears after cleaning, it was likely grout haze or light efflorescence. If the grout still looks chalky, powdery, or is crumbling, you'll need to go further.

Step 2 – Treat Efflorescence

For stubborn efflorescence, you'll need a dedicated efflorescence remover or a diluted phosphoric acid-based cleaner. Always follow the manufacturer's instructions carefully and wear gloves and eye protection — these products can be harsh.

• Apply the cleaner to the affected grout lines.
• Allow it to dwell for the recommended time.
• Scrub and rinse thoroughly.
• Neutralise with clean water and allow to dry.

If efflorescence keeps returning, there may be an underlying moisture issue — such as a leak or inadequate waterproofing — that needs to be addressed first. In wet areas like showers, this is particularly important under the NZ Building Code clause E3 (Internal Moisture).

Step 3 – Regrout if the Grout is Damaged

If the grout is soft, crumbly, or deeply discoloured, cleaning alone won't fix it. You'll need to remove and replace the grout.

What you'll need:

• Oscillating multi-tool with a grout removal blade, or a manual grout rake
• Vacuum and damp cloth
• Pre-mixed or powder grout (match the original colour and type — sanded for joints over 3 mm, unsanded for narrower joints)
• Grout float
• Bucket, sponge, and clean water

How to regrout:

1. Remove old grout to a depth of at least 2–3 mm using your grout rake or multi-tool. Work carefully to avoid chipping tiles.
2. Vacuum out all dust and debris, then wipe joints with a damp cloth.
3. Mix your grout according to the manufacturer's instructions — don't add extra water.
4. Apply grout diagonally across the joints with a rubber grout float, pressing firmly to fill completely.
5. Clean off excess with a damp sponge in a circular motion, rinsing frequently. Don't use too much water.
6. Allow to cure — most grouts need at least 24–48 hours before getting wet. Check the product datasheet.

For wet areas (showers, around baths), consider using an epoxy grout or a polymer-modified grout for better moisture and stain resistance. Brands like Ardex and Mapei offer quality grout products widely available in NZ.

Step 4 – Seal the Grout

Once your new grout has fully cured (check the manufacturer's recommended time — often 7 days for sealers), apply a penetrating grout sealer. This helps repel moisture and staining, and makes future cleaning much easier. Reapply sealer every year or two in high-use wet areas.

Wet Area Waterproofing — Don't Skip This

If you're regrouting a shower or other wet area, check that the waterproof membrane behind the tiles is intact. In NZ, wet area waterproofing must comply with NZ Building Code clause E3. If you suspect the membrane is damaged or was never properly installed, this is a job for a licensed tiler or builder. BRANZ has good guidance on wet area construction standards.

When to Call a Professional

Consider calling a qualified tiler if:

• Efflorescence keeps returning despite treatment (possible leak or waterproofing failure)
• Tiles are loose, hollow-sounding, or cracking — this may indicate substrate movement
• The wet area waterproofing is compromised (this may require a building consent depending on the scope of work — always check with your local council)
• You're unsure of the tile or grout type and don't want to risk damage
• The area is large or the tiling is complex

A skilled local tiler can diagnose the root cause quickly and save you time and money in the long run. You can find qualified tilers in your area on tradedirectory.co.nz.

Sources & Further Reading

• MBIE Building Performance – NZ Building Code
• BRANZ – Building Research
• Ardex NZ – Tile & Stone Products
• Mapei NZ – Grout & Adhesive Products
• Bunnings NZ – Tiling Supplies
• Mitre 10 NZ – Tiling Supplies