Pressure washing safety

Chemicals. Soft washing is a chemical process. Today's Homeowner's mixing guidance uses a quarter gallon of chlorine to a gallon of water (roughly 1:9) with a 25 to 30 minute dwell, or a quarter gallon of bleach to a gallon of water with a 15 to 30 minute dwell, and is blunt about the protective equipment needed because the chemicals can cause second- to third-degree burns. ARMA's roof method uses a 50:50 mix of laundry-strength liquid chlorine bleach and water and advises appropriate PPE plus precautions to protect landscaping.

Plants. Bleach solution running off a roof or wall lands on whatever is below it. Today's Homeowner's practical advice is to over-hydrate plants before cleaning so they absorb less of the solution. A professional crew should be pre-wetting, covering and rinsing plants as a matter of routine - ask what they do.

Heights. Most roof-cleaning injuries are falls, not chemical burns. Combine a wet surface, a bleach solution and a ladder and you have a genuinely dangerous job. Malarkey also notes that excessive walking on shingles dislodges granules and prematurely ages them - so even a successful DIY roof clean can cost you roof life.

The machine. A pressure washer stream can injure skin and drive contamination into a wound. Never point it at a person, never use it from an unstable ladder, and be cautious near electrical service entries, outdoor outlets, light fixtures and meters. Polymeric Exteriors guidance specifically cautions around windows, doors, electrical wiring and plumbing.

Cold weather. There's a safety and damage angle here. NPS guidance advises that water cleaning of masonry should never be done in cold weather or when frost is likely, because water in the masonry can freeze and cause spalling and cracking, and notes a masonry wall may take over a week to dry.