Concrete patio slabs still look like this after thoroughly power washing. Would a liquid patio cleaner help, or do I just need a more powerful power washer? (mine is only 1800w/135bar) :
Millstone Stepping Stone - Minster Paving
How To Clean Paving Slabs? – A Complete Guide | Quick Cleaning Services
Power Washing Paving Slabs in Great Oakley - Patio Stone Cleaning and Maintenance