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.