The chemicals used in pressure-treating lumber, including fire-retardant chemicals, are corrosive to bare steel. The joist hangers used in construction with both sawn lumber and manufactured joists are usually galvanized (zinc-coated). Photos 1 and 2 show galvanized steel joist hangers supporting nontreated lumber joists. Until recently, the zinc coating on the steel joist hangers prevented corrosion by the most common wood preservative, chromated copper arsenate (CCA), and by some fire-retardant chemicals (usually boron- or borax-based). Stainless steel joist hangers are available for contact with more corrosive treated lumber.