Refinishing Fiberglass Shower?
Answers: Try using vinegar, which is mildly sharp and will etch concrete and grout slowly. The coloration in grout is from the use of different minerals, which are held together within a cement base. The vinegar will act in response with the cement, loosening it up and allowing the grout to come free.
mix up some comet and thaw water and filch a piece of leather and rub the spots it will come off
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