Low VOC, high solid deck membranes

A topcoat coating formulation comprising an aliphatic polyurethane pre-polymer having isocyanate terminal end groups, a first solvent and optionally a second VOC-exempt solvent, a catalyst, and at least one filler, in which the total formulation has a VOC content of less than or equal to 95 g/L,

• the prepolymer having an equivalent molecular weight of about 500-10000 g/mol and an NCO/OH ratio of about 1.1 to 3.3, and being the reaction product of about 51 wt % to about 100 wt % aliphatic polyisocyanate, 0 wt % to about 49 wt % aromatic polyisocyanate, and a polyol selected from the group consisting of polyoxyalkylene polyols, polyester polyols, and polycarbonate polyols, wherein the weight percent of polyol to polyisocyanate reacted to form the pre-polymer is in the range of between about 57 to about 87% by weight, based on the weight of the pre-polymer,
• wherein the weight percent of the pre-polymer based on the weight of the total topcoat coating formulation is about 57.7% to about 95%, and the total weight percent solids in the topcoat coating formulation is greater than 82% to about 99%,
• wherein the total formulation viscosity is less than 80 poise at greater than 82% solids, and
• wherein the topcoat coating reaction product has a 100% modulus of greater than 700 psi.