I think you’re lucky to have a stone mason agree to replace it. Often that is a fight in itself. Sounds like a reputable tradesman who is willing to replace it and then use a HEPA vacuum which is the recommended method. But only you can make the decision.

Do you think the removal would generate a lot of dust? The bench is about 3m long and has one waterfall side. Very concerned about toxicity. I live in an apartment.

The amount that you will be exposed to is minute and negligible if your concern is silicosis. This nasty disease is due to prolonged exposure and massive amounts of dust. I work with silica and I would not worry in the least. I think it’s great that the stonemason is willing to rectify.

Thank you.

Hi, I am not sure I understand your reference as to the gap of little over half a millimeter " 0.6mm" and where the gap is IE between wall and splashback or between your top's joints? Do you have a photo of this and can you please check if this 0.6 mm is millimeter or centimeter?

The bench that abutts the wall really should have a splashback too, so as to protect the wall from dirt and water and making it easy to clean. An 8mm to 10mm thick splashback here would be pretty standard and would not look out of place.

Thank you. At one side of the bench the gap is 0.4mm and on the other side it is 10mm, i.e. a difference of 0.6mm. I think I have found a solution to install a tile splashback of approx 10mm along the wall. I really want to avoid any stone cutting in my home.