Method of making a catalytic converter

In a method of making a catalytic converter of the type wherein a monolithic catalyst element is mounted in a metal housing and is resiliently engaged by a compressed blanket of metal wire mesh, the improvement comprising the step of injecting a continuous circumferential band of viscous fiber reinforced high temperature intumescent caulking material which is of substantially less axial length than the axial length of said catalyst element into the interstices of the mesh and throughout its thickness before the mesh and monolithic element are assembled into the housing, said caulking material being expanded by the hot exhaust gases to which the converter is subjected during use, said band of caulking material serving to reduce bypass gas leakage through the metal wire mesh and also reducing the temperature of the metal mesh.