Hammerite Waxoyl Rustproofing for Cars 400ml Aerosol Black. Waxoyl clear is a thick, waxy fluid saturated with a very powerful rustkiller. Spray it on metal and it instantly chases out moisture and forms a flexible weatherproof skin that does not crack, dry out or wash off in the rain.Kills old rust and prevents new rust. Apply to the insides of doors, behind sills and chassis and anywhere that water is likely to collect. Also available in Clear.