Landscape stones, which include items like pavers, decorative rock, and retaining wall blocks, bring structure and appeal to an outdoor area. Over time, exposure to weather, organic debris, and vehicle fluids can lead to the accumulation of dirt and deep stains. Maintaining these surfaces is important for the stone’s longevity, as certain growths and chemicals can cause surface deterioration. Since the composition and porosity of stones vary widely, successfully cleaning them requires targeted methods for different types of buildup.
Initial Preparation and Basic Cleaning
Before applying any specialized cleaning agents, thorough preparation is necessary to remove loose debris and surface dirt. Start by sweeping the entire area with a stiff-bristled broom to clear away leaves, loose soil, and grit. Gather personal protective equipment, such as safety glasses and gloves, for the cleaning steps that follow.
Rinsing the stones with a standard garden hose helps loosen ingrained dirt. For general grime, mix warm water with a mild, non-acidic detergent, like dish soap, and apply this solution with a stiff nylon-bristle brush. Scrubbing in small sections lifts the everyday soiling before a final, thorough rinse is performed to prevent soap residue from attracting new dirt. A pressure washer can be an effective tool for large areas, but it must be used cautiously, set to a low pressure (below 1,500 PSI) and equipped with a fan nozzle to avoid etching the stone surface or blasting out the joint sand between pavers.
Removing Biological Growth
Organic growths like moss, algae, and mold are very common, especially in shaded or damp locations. For a gentle approach, a solution of one part white vinegar mixed with one part water can be applied to the affected area. Vinegar’s mild acetic acid content disrupts the cell structure of the growth, and the solution should be allowed to sit for about 15 minutes before scrubbing.
For more persistent biological stains, a diluted solution of household bleach is highly effective at killing and brightening the affected surface. A mixture of approximately one part bleach to ten parts water is typical for this application. Once applied, the solution should be left for a short period, generally no more than 10 to 15 minutes, to allow the hypochlorite to act upon the organisms. Protect surrounding vegetation by thoroughly wetting them down or temporarily covering them, and then rinse the stone surface completely after treatment to remove all residue.
Treating Specific Stains
Certain non-organic stains require specific chemical reactions for successful removal. Efflorescence, which appears as a white, powdery residue, consists of soluble salts that migrate to the surface as water evaporates from the stone. This mineral deposit can be removed using a commercial efflorescence cleaner or a highly diluted muriatic acid solution, typically 1:12 to 1:21 parts acid to water. Extreme care must be taken with muriatic acid, including pre-wetting the stone, wearing full safety gear, and neutralizing the area immediately afterward with a baking soda and water solution to halt the acid’s reaction.
Rust stains, often originating from metal furniture or fertilizer granules, require a dedicated acid-free rust remover to lift the iron oxide without damaging the stone. These products chemically convert the rust into a soluble form that can be rinsed away, often requiring a dwell time of 5 to 15 minutes. Oil and grease stains, such as those from grills or vehicles, are best tackled initially by using absorbent materials like cat litter or sawdust to soak up the excess liquid. Remaining stains can then be treated with a degreaser or a poultice, which is a paste of a solvent and an absorbent powder that draws the stain out of the stone’s pores as it dries.
Sealing and Preventing Future Buildup
Once the stones are clean and completely dry, applying a protective sealant is a worthwhile step to limit future buildup. Sealing reduces the stone’s porosity, which in turn limits the absorption of water and inhibits the growth of moss and algae. The two primary types are penetrating sealants, which soak into the stone and create an invisible barrier, and topical sealants, which form a protective film on the surface, sometimes adding a glossy or “wet-look” finish.
The selection of a sealant should be based on the stone type and the desired aesthetic. The application requires the stones to be fully dry, often for 24 to 48 hours, and typically involves applying the product in thin, even coats with a roller or sprayer. Regular preventative measures, such as sweeping the stones to remove organic debris and ensuring good drainage, will significantly extend the time between deep cleanings.