April 21, 2022We recently were asked how to remove 3 year-old cement stains from sandstone walls without changing the color of the sandstone. Although this is not a question we get frequently, we thought it was a good one.
First things first. Is the cement chunky?If the cement was splattered (rather than smeared, for example) and looks as though it is sitting on top of the stone, you will want to carefully chip off as much of the chunky bits as possible first. Remember to use safety equipment, such as safety glasses, during this process. No one wants cement in their eyes.
Cleaning with muriatic acidMuriatic acid (also called hydrochloride acid), diluted with water could be used to remove the cement, but since sandstone is often held together with calcite or dolomitic cement, which are broken down by acids, muriatic acid may do more harm than good. Before using any kind of acidic cleaner, it is important to test how your sandstone will react.
To test how your stone will reactDilute one part muriatic acid with six parts water and place a drop in an inconspicuous location. If the drop of diluted acid fizzes, that means the acid is breaking down calcium carbonate within the stone. Do not use an acidic cleaner.
Working with a professionalCleaning with acid can be daunting, and we highly recommend you leave this tricky cleanup job to an experienced, trained stone restoration professional rather than doing it yourself or hiring a handyman who doesn't understand the properties and characteristics of natural stone. We are always happy to answer your questions or provide an estimate.