Q.: Last winter a concrete floor was cast over a vapor barrier on about 3 feet of fill. The floor is used for grain storage so it must be dry; that was the purpose of the vapor barrier. We can't seem to control moisture coming from the floor, or accumulating on the floor by condensation from the high humidity of this summer. The floor does not have a sealer on it, and we are afraid to apply a sealer if not all of the moisture in the concrete has yet evaporated. What can we do to correct this condition, if anything? I have considered the use of a trowel-on emulsified asphalt surface, approximately 3/8 inch thick, over the entire surface. Would such an application reduce the temperature difference between the cold concrete and the warm air of the room, thus keeping moisture from condensing on the applied asphalt surface? We do not have room to increase the elevation more than a fraction of an inch.

A.: Concrete floors, whether over vapor barriers or not, continue to release water by evaporation for a long time after curing. Nevertheless, the problem you describe seems to be primarily one of condensation. You are right in thinking that the solution is to decrease the difference in temperature between the floor surface and the air during periods of high humidity.

Whether 3/8 inch of troweled-on emulsified asphalt would be sufficient for the purpose under the conditions prevailing in your area, we can't be sure. The best approach might be to try various thicknesses of asphalt in an out-of-the-way area of the floor to see how thick an asphalt topping is required to prevent condensation on the most humid days. You must consider, however, that the topping may have poor resistance to gouging from loaders.

If toppings of acceptable thickness are not effective you may have to put in a floor that includes an insulating layer of cellular concrete, perlite concrete, or vermiculite concrete covered with a wear-resistant topping.