Bleach and cleaning chemicals in pressure washing: what homeowners should know
Updated · KeystoneProGuide editorial team
Are pressure washing chemicals safe?
They can be used safely, but none of the sources treats them as harmless. Low-pressure cleaning, which the bodies behind roofs, siding and decks all prefer to high pressure, works by letting a solution do the job, so the chemistry deserves as much attention as the pressure. The cautions below come from the U.S. Environmental Protection Agency (EPA), the U.S. Forest Service's Forest Products Laboratory, the National Park Service and the trade associations for shingles and vinyl siding.
What is the biggest danger with bleach?
Mixing it. The EPA says never to mix chlorine bleach solution with other cleaning solutions or detergents that contain ammonia, because toxic fumes could be produced. A Forest Products Laboratory chemist gave the same warning for deck cleaning: when bleach is used with detergent, use a powdered one, since liquid detergents, particularly those with ammonia, can form noxious vapors with chlorine bleach.
The EPA adds practical precautions for anyone working with a biocide such as chlorine bleach: ventilate the area and exhaust the air outdoors, and wear gloves made of natural rubber, neoprene, nitrile, polyurethane or PVC. The shingle makers' trade association, ARMA, asks for eye protection and rubber gloves when its bleach solution is used on a roof.
Can bleach damage the house?
It can damage some surfaces, by the sources' own accounts.
- Wood decks. The Forest Products Laboratory chemist said laundry bleach tends to cause excessive pulping of the wood surface, particularly on cedar, and that some cleaners are strong enough to pulp a deck. He suggested starting gently, with a cleaner based on sodium percarbonate, or a 4:1 water and household bleach solution with a little powdered detergent.
- Vinyl siding. The siding industry's association, PEPA, lists undiluted chlorine bleach among products that can damage the surface, along with cleaners containing organic solvents, liquid grease remover, nail polish remover and furniture polish. For larger areas of mildew it suggests 30% vinegar and 70% water.
- Shingle roofs. ARMA describes a household bleach and water solution as the one method it accepts, says mixing directions vary by shingle maker, and says other chemicals should not be used without the manufacturer's approval.
- Stone. The National Park Service says alkaline cleaners are generally not recommended for sensitive stone such as limestone or marble, and that where one is used on masonry it should be rinsed from the bottom up and neutralized afterward.
What about plants and the rest of the property?
ARMA says its roof solution should be applied carefully to avoid damage to other parts of the building and the surrounding landscape. PEPA warns that insecticides and herbicides can stain siding, and says to cover brick or stone accents so runoff from washing siding does not reach them. None of the sources read for this guide gives a method for protecting plants, so ask the company what it does.
Is bleach the right answer to mold?
Not as a routine. The EPA says the use of a biocide such as chlorine bleach is not recommended as a routine practice during mold cleanup, though professional judgment may call for it in some cases, and that a background level of mold spores will remain after any cleanup. It says those spores will not grow once the moisture problem is solved. That guidance is written for indoor cleanup; it is cited here for its point about moisture.
When is a cleaner a pesticide?
When it is sold to kill or control a pest. The EPA says a product is likely to be a pesticide if its labeling or advertising claims to prevent, kill, destroy, mitigate, remove or repel a pest, and its list of pesticide types includes algicides, which kill algae, and fungicides, which kill fungi including mildews and molds. Except in limited cases, pesticides must be registered with the EPA before they can be sold.
That matters for who may apply them. Pennsylvania's Department of Agriculture says a commercial applicator license is needed to use pesticides on the property of another, working for a company with a pesticide business license. Its page does not say whether that covers products used to wash houses. If a company's product label talks about killing mold, mildew, algae or moss, ask which license the company holds.
What should you ask about chemicals?
- What products will you use on each surface, and may I see the labels and safety data sheets? The National Park Service tells users to read both and never to use a product off label.
- Is anything you use sold to kill mold, mildew, algae or moss, and do you hold a pesticide applicator license?
- Do you ever mix bleach with other cleaners?
- How will you protect plants, stone, windows and the siding?
- Where will the rinse water go?
On the last point, where pressure washing water goes explains the storm sewer rules. Soft washing vs pressure washing covers the trade-off between chemistry and pressure, and cleaning an asphalt shingle roof gives ARMA's method in full. Companies offering the service are on the pressure washing directory page.
Sources
- A Brief Guide to Mold, Moisture and Your Home, U.S. Environmental Protection Agency
- Springtime Means Deck Maintenance for Many Homeowners, USDA Forest Service, Forest Products Laboratory (news release via Newswise)
- Algae Discoloration of Roofs, Asphalt Roofing Manufacturers Association (ARMA)
- How to Clean Vinyl Siding, Polymeric Exterior Products Association (PEPA)
- Preservation Matters: Maintenance - Graffiti Removal from Historic Features, National Park Service
- What is a Pesticide?, U.S. Environmental Protection Agency
- Types of Pesticide Ingredients, U.S. Environmental Protection Agency
- Pesticide Applicators, Registered Technicians, and Certification Exams, Pennsylvania Department of Agriculture