We have had some moisture problems here when a tile surface is laid over a concrete floor. In these cases we get an extraordinary amount of moisture on the tile surface. In those instances where the tile was torn up the concrete was found to be dry but the tile paste seems to have somehow drawn moisture from someplace. We have had exceptionally high humidity in this state in recent months. Could this have caused our problem?
Since the water did not come through the concrete it would indicate a dense, impermeable concrete of good quality. But since concrete is a good conductor of heat and the temperature of the concrete when this condition occurs is lower than the dewpoint of the warm, humid atmosphere, you will get moisture condensation. If it is an indoor job, general improvement would be obtained by lowering the dewpoint of the air, which can be accomplished by a dehumidifier. Insulation could also be placed between the concrete and the tile but this is rather expensive. A way to test the dehumidifying process is to put two to three pounds of calcium chloride in a wire basket, hang the basket from the ceiling with a pail underneath, on the floor. The amount of water accumulated by the calcium chloride and dripping into the pail will give an indication of the amount of moisture in the air, and noticeable improvement will be found a few days after starting this procedure. The idea is to bring about a balance between the temperature of the surface of the tile and the surrounding temperature so that no condensation will occur.