Boiler pressure processes with creosote have been successfully used to impregnate railway sleepers for more than 150 years: A simple Rüping process is used for oak, pine, and larch sleepers. The improved double ruffling process is used for beech sleepers, and the boiler vacuum pressure process is used for pine sleepers.
For treatment with alternative wood preservatives to creosote – depending on wood species and wood preservative – proven single-stage or a newly developed two-stage has been used for several years.