The mechanical properties of blends of high-density polyethylene (HDPE) with a recycled thermosetting filler, urea-formaldehyde grit (UFG), were evaluated in the range of 0-23% of filler by volume. Ethylene-acrylic acid (EAA) copolymers and an ionomer based on EAA were evaluated as compatibilizers. The observed tensile modulus of the ionomer-treated blends was raised to three times the modulus of virgin polyethylene, whereas the modulus of the untreated blends reached double that of polyethylene. The ionomer-treated blends also showed a higher tensile strength than the blends without filler treatment. The improvement in the properties was assigned to an increased interaction between the filler and the polymer matrix.