Jointing Compound Stains

Green staining on jointing compound (and often on the sandstone itself) is usually caused by algae, moss, or lichen growth due to damp conditions. Here’s how you can remove it safely without damaging your paving or the jointing compound: --- 1. Gentle Cleaning (First Step) Use a stiff outdoor brush and warm soapy water (a mild detergent like washing-up liquid is fine). Scrub the affected areas, especially the joints, to lift algae. Rinse thoroughly with clean water. --- 2. Specialist Patio Cleaner (If Brushing Isn’t Enough) You can use a patio/algae remover such as Wet & Forget, Algon, or similar biocidal cleaners. These are designed to kill algae and slow down regrowth. Apply according to instructions — usually by spraying and leaving it to work over days/weeks. ⚠️ Avoid strong acid-based cleaners (like brick acid / hydrochloric acid) — they can damage both sandstone and jointing compounds. --- 3. Pressure Washing (With Care) A pressure washer can help, but use it carefully: Keep the nozzle on a fan setting, not a jet. Hold it at least 12–18 inches from the surface. Avoid blasting directly at the joints, as this can erode or dislodge the compound. --- 4. Preventing Regrowth Ensure the patio has good drainage and airflow. Regularly brush leaves, soil, and debris off the slabs. Reapply a biocidal cleaner once or twice a year. Consider sealing the sandstone and joints with a breathable paving sealer (but only once the surface is fully clean and dry). --- 👉 Would you like me to suggest safe DIY solutions (like diluted household products) or would you prefer I list the best off-the-shelf patio cleaners in the UK?