Why does white bathroom grouting turn black? And what can be done to prevent it?
鈥� The black staining on the grout is the fungus . It thrives in warm, damp areas, and the grout surrounding bathroom tiles is an excellent habitat for it. Applying neat bleach and bicarbonate of soda, then scrubbing with a toothbrush, will remove the mould. Unfortunately, the fungal cells can penetrate mastic and leave a permanent black stain. If that happens, the mastic will have to be gouged out and replaced.
It is hard to prevent the fungus from appearing in the first place. The tiles need to be kept dry and the bathroom must have good aeration to reduce humidity levels. Regular bleaching of the tiles will also prevent any build-up of mould.
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Peter Scott, Hove, East Sussex, UK
Regular application of neat bleach seems to be the mainstay of readers鈥� grout-whitening methods. A couple of other tactics may be worth trying 鈥� Ed
鈥� Grout turns black when colonised by a fungus. The most common of the species that thrive on grout and bathroom sealants is Aspergillus niger. The microscopic spores are airborne and get everywhere, and the mould is very difficult to remove completely once established in a bathroom or shower cubicle. Bleach and strong detergents may kill the surface of the fungus but not remove the unsightly black staining. In a severe case, the only completely reliable way to remove the stains is to cut or scrape out the old grout and apply it afresh. The sealant will need to be replaced as well.
There are products on the market that claim to be mould and fungus-resistant, but I have yet to find one that lives up to this promise. Over time, any such resistance diminishes, and in a few years the mould takes hold.
The best strategy, once you have cleaned and regrouted the bathroom, is to prevent the spores germinating. Keep your bathroom or shower cubicle well ventilated. Install a good ceiling vent with an extractor fan that stays running for at least 10 minutes after you have turned off the light, or whichever device triggers the fan. After using the shower, take a dry cloth and thoroughly wipe down all surfaces, particularly the sealant joint at the base.
Once the bathroom is ventilated and dry, there is no home for the spores to settle in and cause you anguish.
Simon Young, Horwich, Lancashire, UK
鈥� The blackening of bathroom grouting is usually caused by fungal growth. It is there because the grout provides all it needs: a rough surface, humidity and food. It is easy to see how our bathrooms and showers provide the first two, but few people realise that traces of soap, shampoo and cleaning agents are a rich diet for fungi. I have found that I can substantially reduce the nuisance by frequent, careful washing of vulnerable surfaces with pure water.
鈥淭races of soap, shampoo and cleaning agents are a rich diet for the fungi that blacken grouting鈥�