We washed some round rocks. Washed rock is exactly how it sounds - aggregate and sedimentary material that has been cleaned free from clay, dirt, and other natural debris. While it may not be 100% free from any debris, it is essential for its functionality as a back fill material or as inexpensive decorative spread! The Facts Basic and essential. This Washed Round Rock 40 mm is a basic aggregate that can act as a functional back fill for certain hardscapes such as retaining walls as it allows water to trickle down to permeable fabrics or sleeves. In addition to its functional purpose, it can be used as a decorative rock for landscapes and gardens, however as the washed rock are natural sedimentary materials, the sizing and coloring will be inconsistent throughout. What about Weeds? Relation between Weeds and Washed Rocks. Drawing from our experiences, if you are using the Washed Round Rock as a decorative spread, we would recommend installing a landscaping fabric (5 oz.) underneath. By installing a thicker fabric, it will assist with the following: Separation of topsoil or base material for easy cleaning. Defense against, not the elimination of weeds. The removal of weeds will be easier as the roots of grown weeds will not be able to take heavy root into the soil with the fabric being present.