What the green, black and gray growth on your walls and roof really is, how sodium hypochlorite and other solutions kill it and what to do about your plants.
Mold, mildew and algae are living growth that thrives on Florida walls, roofs and decks. Water pressure alone removes the surface but not the roots, so it comes back fast. Professionals use a diluted sodium hypochlorite (bleach-based) solution with a surfactant applied at low pressure, then rinse and protect plants. You should not run straight bleach through a standard pressure washer pump, and you should never mix bleach with ammonia or acids. Oxygen-based cleaners are a gentler alternative.
Killing the growth at the root is the difference between a wash that lasts a few weeks and one that lasts a year or more.The gray-green film on the shady side of a Florida house is not dust. It is a living colony of algae, mildew and sometimes mold, and it is thriving on your paint, stucco and roof. If you have ever blasted it away with water and watched it reappear a month later, you already know why.
This guide explains the difference between algae, mold and mildew, why sodium hypochlorite is the industry standard for killing them, whether you can use bleach in a pressure washer, and what alternatives exist. For a full-house washing method, see how to pressure wash a house, and for the professional option, our residential team.
| Growth | What it looks like | Where it thrives |
|---|---|---|
| Algae | Green or dark green film | Shaded walls, roofs, damp concrete |
| Mildew | Gray or black powdery patches | Humid, shaded surfaces and painted walls |
| Mold | Black, green or dark spots, fuzzy | Damp areas, gutters, eaves |
| Lichen and moss | Crusty patches or green cushions | Roofs, old stone, shaded ground |
Florida is close to a perfect habitat for all of them: warm, wet, humid and full of shade. Pollen and organic dust supply the food. That is why frequency matters, and why our guide on how often to pressure wash your house exists.
Sodium hypochlorite is the active ingredient in chlorine bleach. Professional soft-wash mixes use it at a controlled dilution with a surfactant that helps it cling to the surface. It oxidizes the growth, kills spores and roots, and rinses away. On roofs and stucco, it is the reason a soft wash outlasts a pressure wash.
This is one of the most-searched questions on the topic, and the answer is: not through the pump. Most consumer pumps are not rated for sodium hypochlorite, and it can damage seals and hoses. Some machines have a downstream injector that mixes the solution after the pump, and dedicated soft-wash systems are built for it. If you are using a garden pump sprayer, apply the solution at low pressure, let it dwell and then rinse.
Sodium percarbonate lifts organic stains and is gentler on plants. Works best on wood and composite.
Used on roofs and siding as a slower-acting killer with less odor.
Mild and slow; suitable for light growth but not for heavy infestations.
Formulated for outdoor use with a specific dwell time and dilution.
Removes surface growth only; the roots survive and it regrows quickly.
Sodium hypochlorite is safe around landscaping when it is used at the right dilution and plants are rinsed. Professionals wet everything before and after, control runoff and sometimes cover delicate plants. The main danger to plants is letting solution pool at the roots or dry on leaves. Keep pets indoors until the area is rinsed. See our safety guide for more.
Heavy black mold, roof growth, large stucco walls and anything that needs a ladder are better left to a crew. A professional has the equipment for controlled application, the right dilution for each surface and the plant-protection routine. See our soft washing vs pressure washing guide, and request a free quote when you are ready.
Growth on your home is a living problem, and it takes a killing solution, not just a stronger jet. With the right mix, a careful rinse and a bit of prevention, your walls and roof can stay clean for far longer.
We restore driveways, roofs, patios, pool decks and commercial properties across South Florida from our base in Sunrise, FL. Free, no-obligation quotes: call (954) 405-6642 or request a quote online.
Send us your address and a few photos. We will come back with a clear, no-obligation price.
Request a Free QuoteCall (954) 405-6642WhatsApp UsServing Sunrise, Plantation, Pompano Beach, Fort Lauderdale, Deerfield Beach and nearby cities.Send us your address and a couple of photos. We will match the solution to your surface and give you a clear price in writing, free and with no obligation.
