Much attention has been focused recently on galvanized reinforcing steel especially since zinc-coated rebars are being specified more frequently for exterior applications where thin concrete coverage is required. Although the design should prevent reinforcing steel from being exposed, these steel is the danger of moisture entering from the surface. Hot dip galvanizing of reinforcing steel after fabrication is an effective safeguard against possible corrosion and resulting red rust, which could bleed through to the surface and cause staining and unsightly discoloration. Galvanizing of reinforcing steel also helps control spalling and cracking of concrete by eliminating rust buildup on the steel. Where bare steel rods are used and red rust forms, corrosion will increase in volume to some 13 times the amount of steel reduced by corrosion. This places strong internal pressure on the concrete. There is a strong evidence that this pressure is responsible for a great deal of cracking and spalling of concrete surfaces. Galvanized rebar probably should be used whenever there is any doubt about the effectiveness of the concrete cover. But other factors also may dictate the specification of hot dip galvanizing. Highly corrosive atmospheres and environments, such as locations near salt water or chemical contaminants, exposed structures, or structures where public safety is a factor, or where minimum concrete coverage is desired, may require its use. Investigations have shown that moisture will penetrate through concrete to the reinforcing even in moderate environments. The cost of hot dip galvanized reinforcing materials cannot accurately be given in a flat cost or cost percentage figure. It will vary considerably with the size, configuration, and quantity of rods to be galvanized and the locale of the galvanizer.