A pressure washer makes quick work of dirt, algae, and grime on driveways, decks, and siding — but used wrong it gouges wood, cracks siding, and injures people. Matching pressure and technique to the surface is key.
Match pressure to the surface
Hard surfaces like concrete take high pressure; wood, siding, and delicate surfaces need much lower pressure and a wider-fan nozzle held farther back. Start gentle and test a small area — you can always increase pressure, but you can't undo gouges.
Technique
Keep the nozzle moving in even, overlapping passes, hold it at a slight angle (not straight on) to lift dirt, and never aim at people, pets, windows, or electrical. On siding, spray slightly downward so water doesn't drive up behind the laps.
What to avoid
Don't pressure-wash asphalt shingles (it strips granules), old or soft wood, painted surfaces you want to keep, or anything that could drive water inside. For mould and algae, a cleaning solution with low pressure often works better than blasting.