Q. I noticed white powder on my concrete basement floor along the full length of one side of the foundation. What is it and do I need to take action? I’ve never had water in the basement.
A. It’s efflorescence, the leaching of lime from the concrete by water. The water is moisture, but enough of it is there to do the leaching. It’s harmless. You can open the basement windows to pull out the moisture. It’s less expensive than a dehumidifier which would also do the trick. You also might consider sealing the concrete or masonry to prevent the water from entering the masonry altogether and put an end to the efflorescence.