Stain file № 6727 · Outdoor · Hard surfaces
How to get mildew out of grout
Assess contamination and moisture; remove growth and dry safely. Never vinegar or mixing bleach. A tough one on grout: expect more than one round.
- Editorial difficulty
- Tough
- Estimated hands-on
- 12 min
- It sets
- as it grows
- Kit
- 0 items
01 The short answer
To get mildew out of grout, work in this order: (1) assess contamination and moisture; (2) remove growth and dry safely. Rinse and dry.
This has a higher editorial difficulty rating. Consider professional cleaning rather than stronger or repeated home treatments.
02 Never do this
- Vinegar. Acid slowly dissolves cement grout, so lines sink and crumble over time.
- Mixing bleach with other cleaners. Bleach with vinegar, ammonia or acidic cleaners releases toxic gas.
03 Before you start
- Use white cloths or paper towels only: coloured ones can transfer their own dye into grout.
- Identify the grout and any adjacent stone; use only compatible products. Acid and abrasives can damage grout or tile.
- Pretest every permitted treatment on an inconspicuous area, including trims, and let it dry. Stop for colour transfer, lightening, rings, stiffness or distortion. A successful spot test does not guarantee the whole item is safe.
04 The method
Assess contamination and moisture
Fix the moisture source and keep other people away from the affected material. Follow public-health mould-cleanup guidance, including suitable gloves, eye protection and respiratory protection. Do not disturb growth with an ordinary vacuum or dry-brush it indoors. Large areas, vulnerable occupants or contaminated padding need professional advice.
Why it works: Mould cleanup requires removal and moisture control, not simply lightening the visible stain.
5 min hands-on
Remove growth and dry safely
For a small area on a suitable hard surface, follow EPA cleanup guidance and the surface maker instructions. Clean with a compatible detergent, remove residue and dry fully. Do not assume that vinegar or an oxygen-bleach stain product disinfects, and never mix cleaners.
Why it works: Routine mould cleanup focuses on removing contamination and correcting moisture; a biocide is not always needed.
5 min hands-on
Rinse and seal
Rinse and dry. Once fully dry, a grout sealer keeps the next spill on the surface.
Why it works: Sealed grout gives you time to wipe up before a stain soaks in.
2 min hands-on
05 Dried, set, or back again?
This has a higher editorial difficulty rating. Consider professional cleaning rather than stronger or repeated home treatments.
Assess the mark only once the item has dried according to its care instructions. If it remains, do not keep repeating or strengthening treatment; obtain advice for the exact material and product.
06 What mildew is made of
- Living mould
- Pigment particles
Mildew can involve fungal growth and staining. Correct the moisture problem, remove contamination and dry the material; killing mould alone does not remove it, and an oxidiser is not always needed or suitable. Porous materials may need professional assessment or disposal.
Mildew can contain pigment particles that do not dissolve readily in water. Many must be lifted with an appropriate cleaner rather than relying on bleach. Avoid grinding particles into the material; pigment chemistry and product formulas vary.
- Mildew is mould growing on the fabric itself. The black or grey dots are living fungal growth and its pigment, and the fibre underneath may already be weakened.
- Brush spores off outdoors first; shaking mildewed fabric indoors spreads them.
07 The material: tile grout
No soaking, so each treatment is applied, given a few minutes, and blotted away.
It tolerates hot water (up to about 60 °C (140 °F)) for the final wash, but only after any protein has been rinsed out cold.
- Cement grout is porous and alkaline; acids such as vinegar slowly dissolve it, which is why acid cleaning makes grout lines sink and crumble over the years.
- Oxygen bleach paste whitens grout without the fumes of chlorine, and works on most coloured grouts too.
The tile grout file rates every common cleaner for it.
08 Next time
Never leave damp laundry or towels in a pile or in the machine, dry everything fully before storing, and ventilate bathrooms.
09 Questions
Can I use hot water on mildew on grout?
Warm water helps here once the first steps are done; stay within the care label (up to 60 °C (140 °F)) and check the stain has gone before any dryer.
Does vinegar help with mildew on grout?
Keep vinegar away from grout. Acid slowly dissolves cement grout and its sealer; use oxygen bleach paste instead.
Can I use bleach on mildew?
Only on white, bleach-safe cotton and only as a last step, diluted per the label.
Will mildew come out of grout completely?
This has a higher editorial difficulty rating. Consider professional cleaning rather than stronger or repeated home treatments.
When should I call a professional?
Cracked or crumbling grout, which needs regrouting, not cleaning.