What is this white powder on my foundation?

Question

Can anyone tell me what this white powder might be? I was ripping up the carpet from my basement when I saw this underneath the padding and on the cement foundation. It's white and cakey.

I at first thought I would just vacuum it up, so I took a wire brush and started rubbing it to break it up into a fine powder so it could be vacuumed. I did that to a portion of it, then I noticed that there is discoloration in the cement underneath the white substance.

It seems that this white powder was probably placed there on purpose to cover up something in the cement. I don't see evidence of a crack there, nor is there cracking anywhere else in the foundation. Could it be mold related? I'm a little nervous to do much else with it until I know what it is. I don't want to undo whatever was done when it was put down.

Answer 1

Looks like effloresence to me, which itself is not harmful, but possibly a symptom, mainly of water movement; I would check perimeter walls for further signs of water infiltration, and make sure water movement outside is properly being handled, i.e. gutters, grading.

Answer 2

Efflorescence, salts rising to the surface due to presence of moisture. Common in cementitious materials where water is present.

You can wash it away with mild HCL solution but the stains will remain. Not much to worry about here. On structural masonry over long periods of time there might be a concern as it could be indicative of structural integrity problem.

Answer 3

Efflorescence, salts... you'll also see it on brick faces. Rookie concrete workers. Was your basement floor poured in winter? They add more "chemicals" into the mix, keep it from freezing, keep it flowing, not hardening as fast.

Those "salts" leach up through the concrete. It is what makes an epoxy floor POP up! Fellows wit experience, can mix a batch, according to the weather, temp, humidity. New guys just follow the sign on the wall.

good luck!