Rustproofing is the prevention or delay of rusting of iron and steel objects, or the permanent protection against corrosion. Typically, the protection is achieved by a process of surface finishing or treatment. Depending on mechanical wear or environmental conditions, the degradation may not be stopped completely, unless the process is periodically repeated. The term is particularly used in the automobile industry. Vehicle rustproofing Factory In the factory, car bodies are protected with special chemical formulations. Typically, phosphate conversion coatings were used. Some firms galvanized part or all of their car bodies before the primer coat of paint was applied. If a car is body-on-frame, then the frame (chassis) must also be rustproofed. In traditional automotive manufacturing of the early- and mid-20th century, paint was the final part of the rustproofing barrier between the body shell and the atmosphere, except on the underside. On the underside, an underseal rubberized or PVC-based coating was often sprayed on. These products will be breached eventually and can lead to unseen corrosion that spreads underneath the underseal. Old 1960s and 1970s rubberized underseal can become brittle on older cars and is particularly liable to this. The first electrodeposition primer was developed in the 1950s, but were found to be impractical for widespread use. Revised cathodic automotive electrocoat primer systems were introduced in the 1970s that markedly reduced the problem of corrosion that had been experienced by a vast number of automobiles in the first seven decades of automobile manufacturing. Termed e-coat, "electrocoat automotive primers are applied by totally submerging the assembled car body in a large tank that contains the waterborne e-coat, and the coating is applied through cathodic electrodeposition. This assures nearly 100% coverage of all metal surfaces by the primer. The coating chemistry is waterborne enamel based on epoxy, an aminoalcohol adduct, and blocked isocyanate, which all crosslink on baking to form an epoxy-urethane resin system. E-coat resin technology, combined with the excellent coverage provided by electrodeposition, provides one of the more effective coatings for protecting steel from corrosion. For modern automobile manufacturing after the 1990s, nearly all cars use e-coat technology as base foundation for their corrosion protection coating system. Aftermarket Aftermarket kits are available to apply rustproofing compounds both to external surfaces and inside enclosed sections, for example sills/rocker panels (see monocoque), through either existing or specially drilled holes. The compounds are usually wax-based and can be applied by aerosol can,