Recycling as an economic disposal process for many hazardous waste materials has become a popular means of conserving our planet's scarce and diminishing natural resources. This paper is a study of the influence of oil sludge (OS) on the physical behavior and performance of asphalt filled with heavy oil fly ash (HOFA), cement kiln dust (CKD) and limestone dust (LMD). Conventional asphalt consistency tests in addition to a new bond strength (BS) test were conducted on the modified asphalt mastics. The results were statistically analyzed and assessed in accordance with American Society for Testing and Materials (ASTM) D 332 and ASTM D 449 specifications. Too much OS resulted in strength deterioration of the asphalt mastic, which can be compensated for by filling the mastic with HOFA. OS interacts constructively with the fillers to improve their effectiveness in raising the softening point (SP) and viscosity of the asphalt, and also in reducing its penetration and ductility. Even though sludge mastics hold promise as suitable composites for damp proofing and waterproofing, the resulting low flash point (FP) and SP of some of these mastics make their suitability for roofing applications questionable.