Whether you have just finished building a stone wall, or you simply were left with some residual concrete after removing a slab that was built on stone, you can try to remove it on your own. The difficulty of the task depends on how much residue remains on your stone structure and whether you work on a wall or a floor made of stone.
Strike at the larger bits of concrete with a putty knife lightly at a perpendicular angle. Do not get carried away with the beating, as this might damage the stone underneath.
Beat away on the concrete you just struck using a rubber mallet and a chisel positioned at a 60-degree angle from the wall. Use light tapping as opposed to full-blown forceful hammering. When the concrete begins to chip away, repeat the process on another patch of concrete.
Put a sanding pad on an orbital buffer and turn the device on. Move the buffer along the concrete bits in a circular motion. Do not allow the buffer to touch the stone. Sand down the concrete until only a thin stain of it is left.
Clean out all of the dust from the surface with a brush.
Ventilate the room by opening the windows before continuing any further. Put on some safety gloves and goggles.
Pour 1 qt. of muriatic acid into 2 1/2 gallons of water. This diluting ratio prevents damage to the stone.
Dip a naturally bristled paintbrush into the solution you just created and paint it on the concrete you want to remove. Do not paint further than the concrete. Leave this solution alone for about 15 minutes.
Brush the concrete with a scrubbing brush and spray it off with water. Get plenty of water on the stone to prevent the muriatic acid from settling on it and staining it.