Concrete block retaining walls look great and add a lot of appeal to your landscape. But over time they can become dull and dirty, as organic materials become lodged in the crevices. If you are noticing that dirt, mildew or some other unwanted substance has taken over your once beautiful wall, then it’s time to get out the garden hose and give the wall a good cleaning.
You may be tempted to pull out the big guns and attack the problem with a power washer. However, a spray attachment to your garden hose and a little dish soap will usually do the trick. In most cases this will clean the wall and make it look new again. If there are stubborn stains that resist the garden hose approach, you may need to power wash. When using a power washer, make sure to use the broadest, lowest-pressure nozzle that will clean the surface. A nozzle that is too narrow may cut into the block, causing irreparable damage. Also, hold the wand at the correct distance to deliver the necessary pressure without damaging the block.
While dish soap will clean most walls, sometimes stronger cleaning detergents may needed where stains are not water soluble, or are caused by air pollutants. There are many products available, and local wall suppliers can recommend a detergent that is safe for concrete products. (Find one near you) Read the labels and be sure to protect any plants that you don't want damaged.