Question: “My limestone kitchen counter has developed black speckled marks, especially around the sink. This leads me to believe it may be mildew from dampness. How can I remove these stains before sealing? Every blog says no acidic cleaners, but how about bleach?”

Answer: The blogs you have read are correct, Limestone is sensitive to acids so you keep them away from the counter-top. In fact the term acids also encompasses vinegar, wine, lemon/orange juice and various other household substances and foodstuffs, so you are going to have to be extremely careful with your counter-top – especially if you are intending to use it a lot for food preparation (make sure you take precautions like using chopping boards and don’t let any acidic liquid linger. Wipe it up as soon as you notice any splashes etc.

OK, what about bleach? Well, bleach is not an acid, in fact is it the absolute opposite – it’s an alkali (base), but a very strong one. Even though it is not an acid, as it is such a strong base, it can cause some problems of it’s own, particularly if a stone has prolonged or repeated exposure to it. If it does not affect the stone, it can affect any sealer that may be present. However, if you take some ordinary household bleach and dilute it down with some water, say 50:50 and apply a little to the affected area, then leave it for about 30 minutes. After this you should see a significant reduction in the black mildew (if that is what it is). If so, now you need to rinse with clean water and wipe it down. If there are some stubborn areas, you could boost the cleaning with the addition of a little Nanoscrub.

Once it is clean and dry, you could use also consider using Sealer’s Choice Gold to seal.