Try a stiff brush and some alkaline cleaner.
HI,we are finishing up a terrazzo floor project in which we polished the floors ad baseboards. we are having a really tough time getting some white spots out of some corners and seams. I am going to try some impregnating color enhancing sealer. Am concerned about using any acid cleaner but the neutral cleaner is not budging all of it. some of it is powder form the polish, but there are areas where we just couldn't get into the corners with anything very small. Would appreciate any ideas. Some not very good pictures below.
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