Green and black streaks on a wall, slippery moss on a walkway, dark patches spreading across roof tile. Algae, mold and moss grow wherever porous surfaces stay damp and shaded. They look neglected, they make walkways slippery, and over time they hold moisture in the surface and speed up wear.
Most sites deal with it the same way: pressure-wash it off, then watch it come back a few months later. The fix is not just cleaning harder. It is cleaning, then protecting the surface so growth cannot take hold again.
Why it keeps coming back
Concrete, brick, stone and roof tile are full of tiny pores. Water sits in them, and spores settle in that water. Washing removes what you can see, but the surface is just as porous and damp as before, so growth returns as soon as conditions suit it. North-facing walls, shaded paths and areas near sprinklers or drains are usually the worst.
1. Clean it back to the bare surface
Remove all existing algae, mold, dust and dirt. Pressure-wash if needed, then let the surface dry fully. Any growth left behind will carry on underneath a coating, so take the time to get it clean.
2. Test and protect the surroundings
Mask off nearby areas with painter’s tape and test a small, hidden spot first. Take care around ponds and sensitive plants.
3. Apply a protective coat
Algae Guard is a bio-based, water-based coating with zero VOCs (no harmful fumes) that helps stop algae, mold and moss coming back. It is clear, water repellent and antibacterial, and it keeps the natural look of the surface.
- Shake the container for several minutes, and again every 15 to 20 minutes while you work.
- Spray with a trigger, pump or airless sprayer. A roller works too, but spraying is recommended.
- Apply a generous, saturating coat in a circular pattern.
- After 2 to 5 minutes, apply a second coat while the first is still tacky. On walls, start at the top and work down.
It is touch dry in minutes and fully cured in 12 hours. Apply outdoors between 45°F and 105°F, at 90% humidity or less.
Where it works, and where it does not
Algae Guard suits cement, concrete, stone, grout, masonry block, brick pavers, walkways, driveways, roof tile, composite and slate shingles, wood fencing and some vinyl siding. Do not use it on polished limestone or marble, because it can dull the finish. It is not for ponds or pools.
Keeping it clean
- Hose off outdoor surfaces from time to time. No harsh chemicals needed.
- Expect 6 months to 2 years of protection under normal conditions.
- To reapply, repeat the same steps. There is no need to strip the first coat.
- For brick, block and stone walls that also need waterproofing, Natural Seal is a breathable water repellent with anti-algae protection built in.
Not sure which product fits your surface? Send us a photo and the area, and we will recommend the right product and how many pails you need.
