a method method for continuously preparing thermo - crosslinkable and / or thermoplastic elastomer blends by mixing the powdered or granulated elastomer with plasticizer oil and other additives , said method comprising the steps of : continuously premixing said elastomer in a premixer with at least part of said plasticizer oil , and optionally with at least part of said other additives , to form a preblend in which said elastomer is decomposed and said additives are embedded in the polymer matrix ; and thereafter continuously completing the mixing of said premix , and optionally of the remainder of said additives in a mixing extruder .