What Is That Black Stain On Your Concrete? Lichen!
This is an update for a post from earlier this month about a failing epoxy garage floor. We went back to tackle a nasty lichen stain in front of the garage.
If you've ever wondered what that black stain is on your driveway or patio, it is most likely a lichen stain. Lichen is an algae-like organism that thrives in moisture and shade, and once it takes hold in porous concrete, it will stay there until it is removed by force!
This was the situation for this driveway. The garage faces North with a small overhang. The overhand is just enough to shade this area most of the time. Combine the shade with an overflowing gutter, and you get the perfect place for Lichen growth.
Of course, this was nothing a thorough steam cleaning couldn't handle!
If you tackle a lichen stain on your own, you will need some serious chemicals and time. However, we use 200° water flowing at 5 gallons per minute at 1,500 psi, so we took care of it in about 15 minutes.
FYI, 1,500 psi doesn't sound like much pressure, but this concrete was seen better days, so any more than that can damage what little finish it has left.
Fortunately, heat and volume do all the heavy lifting when Pressure Washing concrete!
