My house is one year new construction. I didn't use the dehumidifier at the basement until one month ago I realized the basement was damp and there were some mold on the wood frame on the basement ceiling(not serious, already cleaned). I also noticed there are many black spots on the plywood on my basement ceiling and the plywood behind the electrical panel, they don't look like mold to me, but I am not sure. Can someone please tell me what are these black spots? I am concerned they might be mold.
Occasionally there is an error and ink is splattered during the time the sheet is passing through the conveyor getting trimmed,stamped,edges painted,etc...
Looking at your first picture we see the pattern of black spots stops at the joint between two sheets. That assured me that this is not a case of mold growing.
Well that’s not plywood but it is OSB , high moisture in the air can allow mold like you have. A simple 3% hydrogen peroxide and water will stop it from getting worse. I currently work in a mill and the wood stored outside prior to finishing and a biocide spray looks just like this. The only way to prevent it from returning or getting worse is to remove the moisture as you have found your dehumidifier will remove the moisture, I have also found sealing the floor with epoxy paint really helped reduce the moisture but I did still need the dehumidifier just did not need to empty it as often.