If you own a home near Lake Murray, you have probably noticed green or black growth on the siding, the dock path or the deck. It is not because the home is neglected. It is because the lake area gives algae and mildew almost everything they want. This guide explains what you are seeing, why lake homes are hit harder, and how to clean it and slow it down.
What is that green and black stuff?
The stains people call “mold” are often a mix of things:
- Algae: green or black streaks, often on shaded siding and on roofs. This is the most common one.
- Mildew: gray or black spots and a powdery film, often on damp, shaded siding, trim and soffits.
- Moss: thicker, fuzzy growth, usually on roofs and shaded concrete.
- Lichen: crusty patches that cling tightly to surfaces.
They all need the same basics: moisture, shade, something to grow on and time.
Why Lake Murray homes get it worse
More moisture in the air. Being close to the water means humidity is higher more of the year, and surfaces dry more slowly after dew or rain.
Shade from mature trees. Lake lots often have large pines and hardwoods in Chapin, Irmo, Ballentine and Lexington. They drop needles, leaves and pollen, and they keep walls and roofs in shade where moisture lingers.
Low or sheltered spots. Walls near hedges, under decks or close to the ground get little sun or airflow.
Dock paths and lawn edges. Concrete near the water stays damp and grows algae quickly. These surfaces also get slippery. See our dock and lakefront cleaning and driveway and concrete cleaning pages.
Pollen and debris. In spring, pollen settles on everything. Mixed with moisture, it gives algae a place to start. See prepping your exterior for spring pollen.
Where to look first
Growth shows up in these spots before anywhere else:
- The north side of the house
- Siding close to the ground and behind shrubs
- Porch ceilings, soffits and the underside of decks
- Shaded roof slopes
- Concrete steps, walkways and dock paths
- Wood decks, railings, benches and fences
Why it matters
Mostly it looks bad, and that alone is a reason to clean it. But there are practical reasons too:
- Slippery surfaces. Algae on walkways, steps, docks and decks is a slip hazard, especially when wet.
- Moisture held against surfaces. On a roof, growth can hold moisture against shingles. On siding, it keeps surfaces damp.
- Curb appeal and resale. Stained siding and roofs make a home look older and less cared for. See cleaning your exterior before selling.
What helps slow it down
You cannot stop algae in this climate, but you can slow it.
Let in sun and air. Trim back branches and shrubs that crowd the house or hang over the roof. Drier surfaces grow less.
Keep gutters flowing. Clogged gutters send water over the edge and down the siding. See gutter clean-out.
Check sprinklers. Spray that hits siding every day keeps it wet. Aim heads at the lawn.
Clear debris. Sweep needles and leaves off roofs, decks and walkways from the ground when you can do it safely.
Clean on a schedule. Cleaning before growth is heavy is easier than cleaning after it has set in. See how often to wash your house in SC.
Why scrubbing and pressure are not the answer
It is tempting to attack algae with a stiff brush or a pressure washer. On siding and roofs, both can do harm: scrubbing can scratch, and pressure can drive water behind panels or strip shingle granules. And because algae is living, force alone can leave some behind, so it returns.
A soft wash applies a cleaning solution at low pressure to treat the growth, then rinses it away. Our post on soft washing versus pressure washing explains the difference, and our house washing page covers the process.
Decks, docks and brick
Different lake surfaces need different care:
- Wood decks and docks hold moisture, go slick and gray, and can be damaged by too much pressure. See deck cleaning.
- Concrete walkways and boathouse patios need a cleaning solution plus the right rinse. See dock and lakefront cleaning.
- Brick and chimneys darken with mildew and algae and need a gentle approach. See brick and chimney cleaning.
If you have a lakeside deck or dock, tell us the material when you request a quote, since the right approach depends on it.
What results to expect
Most algae and mildew stains clean up well. A few caveats:
- Heavy, long-standing growth may take more than one visit.
- Some staining, such as deep discoloration, may lighten without disappearing.
- Growth will come back over time, faster in shade and damp spots. Regular cleaning keeps it manageable.
We tell you what we expect before we start.
Questions we hear from lake-area homeowners
Is the black stuff on my roof dangerous? Usually it is algae, which is mostly a cosmetic and moisture issue rather than a health concern. If you are worried about mold inside the home, talk to a qualified specialist, since exterior cleaning does not address indoor air or moisture problems.
Why does one side of my house get it and not the other? Sun and airflow. The side that stays shaded and damp grows algae first, which is why the north side is usually the first to go green.
Will cleaning hurt my lawn or the lake? We rinse and protect plants and take care with runoff, especially near the water. Tell us if your property sits right on the shoreline so we can plan around it.
Can I stop it from coming back? Not entirely, but sun, airflow, clear gutters and regular cleaning all slow it down.
Get a clean, safe lake home
If your siding, roof, dock path or deck has gone green, we can help. Request a free quote or call (803) 528-1996. We are based in Lexington and Red Bank and serve Irmo, Chapin, Ballentine, Gilbert, Columbia and the area around Lake Murray. We respond within 24 hours.