Abstract: A method of filling a seam of a structural panel assembly utilizes a non-foaming, thixotropic, two-component polyurethane elastomeric material. The thixotropic, elastomeric material is prepared by rapidly mixing and initiating the reaction of a first thixotropic component comprising an isocyanate-terminated compound having at least two reactive isocyanate groups and a second thixotropic component comprising a hydroxyl-terminated compound having at least two reactive hydroxyl groups. Each of the first and second thixotropic components include from about 3% to 8% by weight fumed silica. The second thixotropic component also includes from about 10% to about 50% filler. The thixotropic elastomeric material is applied over the seam of a panel assembly. The method then includes fluidizing the thixotropic elastomeric material and driving the thixotropic elastomeric material into the seam of the panel assembly.