Stone walls may seem impenetrable, but there are ways to destroy stone. Improper chemical application can damage stone irreversibly. Therefore, it is important to know just how to clean the stone walls of your home or garden. As a general rule, the most effective cleaner of stone is plain water, applied in an effective way. For stubborn stains, you can use mild cleaners. The most important thing to remember is to avoid highly acidic or chemical cleaners, as these can soak into the stone and damage it permanently.
Soak the wall with a garden hose. If possible, use a heavy spray nozzle on your hose. The pressure will remove a lot of surface dirt and grime alone.
Mix warm water and dish detergent in a bucket until the mixture forms suds.
Soak the bristles of your scrub brush in the soapy water. Scrub at the wall to remove dirt, grime and other stains. Repeat as necessary to remove stains and dirt from the stone wall.
Rinse the wall thoroughly with the hose again to remove loosened dirt and residual soap.
Fill the power washer with plain water. Do not add chemical cleaner unless you have consulted the manufacturer to determine what is safe for use on the wall.
Stand at least 120 cm (4 feet) from the stone wall and start the pressure washer. Adjust the level of pressure and your standing distance as necessary to reach the wall and remove the dirt.
Move the pressure stream evenly and continuously across the wall, starting at the top and working your way down.
Step back 30 to 60 cm (1 to 2 feet) after the initial cleaning and begin again at the top. This second cleaning will allow you to remove loosened debris from the wall.
Rinse any spills on the wall immediately to avoid staining. Perform regular cleaning of the wall every two to three weeks to avoid permanent staining and the need for large-scale cleanings. When power washing, move the stream of water in close, circular motions around tough stains for more effective removal. If you have particularly tough stains that are not removed with basic washing, consult the stone's manufacturer for tips about products that are safe for use on the stone.
Power washers are extremely powerful tools. To avoid injury or damage to your stone wall, do not attempt to use a power washer unless you have previous experience. Consult an expert or stick with your garden hose if you are unsure about the use of a power washer.