The Power Washer Trap
Spring arrives. Your Kandla Grey Sandstone patio is green with algae. You rent a heavy-duty industrial pressure washer. You blast the stone at close range. It looks clean!
The Damage: You have likely stripped the top 1mm of the stone surface (delamination). You have blasted the sand out of the pointing (mortar joints), creating gaps for weeds. And you have opened up the capillaries of the stone, meaning it will absorb dirt faster next time.
The "Soft Wash" Protocol
Professional landscapers don't use high pressure; they use chemistry.
1. Biocide Treatment: Apply a high-quality biocide (Benzalkonium Chloride) to the dry patio.
2. The Wait: Let it sit. The chemical kills the algae root system and breaks down the black lichen spots over 24 hours.
3. Low Pressure Rinse: Rinse with a garden hose or a pressure washer on a very low "fan" setting, holding the lance at least 30cm away.
This method preserves the structural integrity of the stone and the joints. It keeps your patio looking new for 20 years, not just 2 years.
