Four classifications of linings are considered here: organic resin, organic elastomeric (liquid and sheet applied), inorganic cementitious monolithic, and inorganic masonry. This chapter suggests tests for providing uniform means for comparing and evaluating various lining materials for use in FGD units. These tests are summarized in Table 5-1. Acceptance criteria are not defined. The proposed tests may or may not be applicable to each zone or environmental severity level. A test that is applicable for one zone may not be applicable to other zones. These tests should not be construed as replacing the need for full-scale testing of lining systems in actual FGD operating units.