The shortcomings of most slab on ground construction have far more to do with faults or oversight of workmanship than to inherent shortcomings in concrete itself. Moisture control is one of the most serious problems which arise in connection with slab on ground construction. The chief complaints on this score relate to the passage of excessive amounts of water vapor through the slabs and to the frequent failure of floor covering materials due to actual transmission of moisture through slabs. Other problems are caused by slab movements sufficient to damage floors and other structural elements and perimeter heat losses which may cause condensation difficulties and excessive fuel bills. To combat the moisture problem there are many vapor barrier materials on the market today. They include papers, plastic films, combinations of paper and plastic films, felts, glass and mineral fibers, mineral aggregates, metals and asphalts. In selecting a particular material the user should be guided by the manufacturer's reputation, backed up whenever possible by his own experience. In addition to providing an effective barrier against water vapor, the selected material should be capable of standing up under the rough handling and heavy traffic which are inevitable on all construction sites.