When last we visited the mystery stairs of wetness, we concluded that the stairs were wet because of moisture being transferred through the cinder block wall that was touching it. I now know this is wrong. I cut away parts of the stair to create a 1/2″ air gap. The stairs are STILL wet. The humidity in the basement is near 90% all the time.
New theory: There is apparently some chemical contamination on some of the stairs that caused them to condense moisture from the air.
I finally got the HVAC running and in it’s new location in the basement, the main level and the basement both benefit from drying air conditioning. between that and a dehumidifier, they are pulling a gallon of water and hour out of thin air. I managed to lower the humidity to 50% (measured) and the stairs dried overnight.
There is no telling what chemical caused this. I can’t tell if washing the stairs will fix it or if they need replacement. But since full replacement is in the plan anyway, it is moot.