Q. I have a 23-year-old concrete deck around my in-ground pool. After power washing it (just water) for 13 years, I noticed that the finish was mottled. Then I began using a 3-to-1 water-bleach mixture with a deck brush and elbow grease. The deck became clean, and so did the mottled sections. Then one spring I noticed real pockmarks in one section of the concrete, spalling of the mottled sections, like little craters. No winter chemicals ever touch the deck. The mottling doesn’t appear to have gotten worse, but the mottled sections do seem to absorb water differently — they dry faster, further highlighting the mottled effect. Is there a cause and the cure?
— CARL J. ZACK, BROOKLINE CARL J. ZACK, Brookline