We have black mould on our bathroom grouting. The grout itself is stable and not crumbling. Before I start a potentially messy and awkward project, can anyone tell me if this is a sign there are serious hidden problems (i.e. damp going on behind the tiles) or is it something that should be treated for aesthetic reasons? I am thinking of treating it with bleach and if unsuccessful, will re-grout.
In most cases this is just an asthetic thing - due to the levels of moisture and temperature change in a bathroom, this can produce the idea conditions for the mould to grow. Unless any areas of the grout have been compromised e.g. split, cracked etc.... then it should remain water tight.
Signs of something more sinister going on normally come in the form of orangy, yellowy, brownish stains on the grout, and not the typical black mould buildup. If you have odd coloured stains then this may be the sign of someting else.
There are quite a few different recipes online for home made grout cleaners - bleach with bicarbonate of soda and peroxide can sometimes work, but there are many others so may be worth Googling and experimenting
Other than that there are purpose made grout cleaners and colouring kits available on the market with a lot of mixed reviews of how successful they actually are, but as you say, the other choice is to regrout.
In order to prevent mould growth in the future, when bathing or showering, try to leave a window open slightly and also have an extractor fan on if you have one (if not, certainly worth getting one installed)
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