Why chemistry matters in exterior washing
Water alone is not an effective exterior cleaning agent for biological contamination. Algae, lichen and mould require appropriate chemical treatment to be killed, not just displaced. The choice of chemistry, what it contains, how it's diluted, how it's applied and how it's rinsed, determines both the effectiveness of the clean and the safety of the process for surfaces, people and the surrounding environment.
As a premium property owner, you have good reason to ask these questions before allowing any chemicals to be applied to your home. This guide gives you an honest overview of what professional exterior washing involves.
Common professional exterior washing chemistry
Sodium hypochlorite (diluted bleach solutions)
Effective biocide for algae, mould and mildew. Widely used in soft washing. At professional dilution rates (typically 0.5–3%), it is effective against biological growth and degrades rapidly once diluted and exposed to sunlight and air. Should not be used on sensitive metals or in concentrations that risk surface bleaching.
Sodium hydroxide (caustic soda), low-concentration solutions
Used in some surfactant-based cleaning solutions for heavy soiling. Requires care in application and thorough rinsing. Not appropriate for all surfaces.
Surfactants and wetting agents
Reduce surface tension to help cleaning solutions penetrate and coat surfaces evenly. Generally low-toxicity and biodegradable at professional concentrations.
Biocides and algaecides
Specialist formulations designed to kill algae, lichen and mould while providing residual protection against regrowth. Active ingredients vary by product; professional providers use formulations appropriate to the specific contamination type and surface.
Sodium percarbonate
An oxygen-based cleaner effective for certain organic stains. Breaks down to sodium carbonate and hydrogen peroxide in use, generally considered environmentally preferable to chlorine-based solutions for appropriate applications.
What a responsible provider should tell you
A professional exterior washing provider should be able to tell you clearly what chemistry they plan to use, why it's appropriate for your surfaces, and how they manage runoff and environmental protection during the job. If a provider is unable or unwilling to answer these questions, that is a significant red flag.
At Prevent Maintenance, we select products appropriate to each surface and situation, apply them at correct concentrations and manage runoff responsibly. We're transparent about what we use and why.
Your questions answered
Our Environmental Promise
Environmental responsibility is built into our operating standards. We use low-toxicity, biodegradable products where possible, manage runoff actively and protect surrounding environments during all exterior maintenance work.
Read Our Environmental Promise