Who this guide is for
- Homeowners with grout that has darkened, stained or gone patchy
- People preparing to brief a tiler or a professional about possible moisture
- Anyone whose grout discoloration returns after cleaning
- Owners wanting a clear record before an assessment
Surface soiling versus deeper discoloration
Note whether the discoloration wipes away with light cleaning or returns and spreads. Grout that darkens in a pattern, especially low in a shower or along a wet edge, is worth recording carefully.
Describe colour and spread rather than deciding whether it is dirt, mould or moisture; a professional weighs that.
- Even soiling across high-touch areas
- Patchy darkening that returns after cleaning
- Black or green specks in damp corners
- Discoloration spreading along a wet edge
Where the discoloration sits
Map which joints are affected — shower base, around the bath, behind a tap, kitchen splashback, or floor. Wet zones and poorly ventilated corners are common spots.
Note whether nearby sealant is also discoloured or failing, as that often accompanies grout problems.
Moisture and ventilation clues
Record whether the room is slow to dry after use, whether condensation forms, and whether there is a musty smell. These are observations that help a professional judge whether moisture is feeding the discoloration.
Note if the affected area stays damp long after a shower or wash.
Photographing without treating
Photograph the affected joints in good light, close and wide, and keep dated images to show whether it spreads. Avoid bleaching or scrubbing hard before assessment, which can mask the pattern.
Note the room and which joints are worst.
- Close and wide shots in good light
- Date images to track spread
- Avoid bleaching before assessment
Briefing a professional
Bring your photos, the joint map, and your ventilation notes before contacting a tiler or, if growth is suspected, an appropriate professional.
Let them establish whether it is soiling, sealant failure or moisture; your record focuses their look.
Documentation checklist
- 1Note whether the discoloration wipes away or returns and spreads
- 2Record the colour and pattern of the staining
- 3Map which joints are affected and in which room
- 4Note whether nearby sealant is also discoloured or failing
- 5Record whether the area stays damp or the room is slow to dry
- 6Note any musty smell or condensation
- 7Photograph close and wide in good light, dated
- 8Avoid bleaching or hard scrubbing before assessment
Common mistakes to avoid
- Bleaching the grout before recording the pattern, which masks the cause
- Assuming all dark grout is mould, or that it is only dirt
- Regrouting over a damp joint without addressing the moisture
- Ignoring failing sealant alongside the grout
- Treating suspected mould yourself rather than having it assessed
When to involve a professional
- A tiler can assess grout and sealant condition, and where mould or moisture is suspected an appropriate professional should assess it
- Do not treat suspected mould growth yourself; persistent or spreading growth is a job for a qualified professional
- If the area stays damp, a ventilation or moisture professional may be relevant
- What is involved varies by location and cause, and requirements differ by project
Frequently asked questions
Questions readers ask about this topic
Is dark grout always mould?
Not always — it can be surface soiling, ingrained dirt, or moisture. Discoloration that returns after cleaning, spreads, or appears as specks in damp corners is worth recording for a professional rather than assuming the cause.
Should I bleach it before taking photos?
Bleaching first can mask the very pattern a professional needs to see. It is more useful to photograph the discoloration as found, note whether it returns after cleaning, and leave treatment to an appropriate professional.
Could discoloured grout mean a moisture problem?
Persistent discoloration in wet, poorly ventilated areas can indicate moisture sitting in the joints. Note whether the area stays damp and whether there is a musty smell, and raise it with a professional.
Can I just regrout over it?
Regrouting over a damp or mould-affected joint without addressing the moisture often sees the problem return. Document the pattern and let a professional establish the cause before any regrouting.
Keep reading