An SBR rubber unit that provides for shimming uneven surfaces to a level plane. The SBR rubber units are recyclable, 1/8? (3.18 mm) thick manufactured to coincide with Terra-Tab sizes. Irregularities in deck sub-surfaces will increase the number of shims required. Optional ?? - #5 shims are available upon request. Spacers: SBR rubber units. Allows for 1/8? or 3/16? spacing used in conjunction with Terra-Shim plates. All rubber products are recyclable. Terra-Tabs and Terra-Shims can be set directly on the waterproof membrane, on an optional protection board or insulation without harm.