Minor Observation

I walked barefoot to the mailbox this afternoon. It is three houses down. After the first house I noticed the texture of the sidewalk changed, much sharper, like walking on fine gravel or coarse sandpaper. Then I noticed the color was different, much whiter that the usual gray. Someone got out their pressure washer and washed away all the mold and lichen. You can see the difference between the white sidewalk in the foreground and the gray sidewalk on the other side of the mailbox. On the way back I noticed that the driveways (that had not been pressure washed) were not as dark as the sidewalks, but they were not perceptibly coarser. The automobile tires must be scrubbing the mold and lichen off the concrete. Actually, probably just the mold. I don't think the lichen gets a chance to get started on the driveways.

So the question is, did the power washing just remove the lichen and mold, or did it also remove a thin layer of concrete, which left the points of gravel sticking up? As sharp as it was, I am thinking the later.

Update February 2017 replaced missing picture.