Rail decontamination machine, comprising - a first excavation device for excavating the ballast of the existing ballast layer, - a second excavation device for excavating an existing formation protection layer below the existing ballast layer, - a first FPL conditioning unit for screening and/or crushing coarse constituents of the excavated formation protection layer, - a first old FPL conveying device for conveying the excavated formation protection layer from the second excavation device to the first FPL conditioning unit, - a second FPL conditioning unit for conditioning the excavated formation protection layer, which comprises a mixing device for mixing the excavated formation protection layer with a liquid conditioning fluid, - a second old FPL conveying device for conveying the partially conditioned formation protection layer from the first FPL conditioning unit to the second FPL conditioning unit, - a conveying line for conveying a liquid conditioning fluid from a fluid tank unit to the mixing device, - an FPL introduction device for introducing the new formation protection layer, - a ballast introduction device for introducing a new ballast layer onto the intermediate layer, - wherein the FPL conditioning unit comprises a screening device for screening out coarse constituents from the excavated formation protection layer, characterised in that the FPL conditioning unit comprises - a crusher for crushing the screened-out coarse constituents of the excavated formation protection layer, - a coarse particle conveying device for conveying the screened-out coarse constituents of the excavated formation protection layer from the screening device to the crusher, and - a fine particle conveying device for conveying the crushed coarse constituents from the crusher and the screened fine fractions from the screening device to the mixer, wherein the conveying line for conveying a liquid reconditioning fluid from a fluid tank unit to the mixing device comprises: - a mixing control unit, - a first connecting line (73 a, b) which connects a fluid reservoir for a conditioning binder fluid to the mixing control unit, - a second connecting line which connects a water reservoir to the mixing control unit, wherein the mixing control unit is designed to establish a mixing ratio between the supplied conditioning binder fluid and the supplied water and to feed the conditioning binder fluid/water mixture to the mixer of the second FPL conditioning unit. - a first excavation device for excavating the ballast of the existing ballast layer, - a second excavation device for excavating an existing formation protection layer below the existing ballast layer, - a first FPL conditioning unit for screening and/or crushing coarse constituents of the excavated formation protection layer, - a first old FPL conveying device for conveying the excavated formation protection layer from the second excavation device to the first FPL conditioning unit, - a second FPL conditioning unit for conditioning the excavated formation protection layer, which comprises a mixing device for mixing the excavated formation protection layer with a liquid conditioning fluid, - a second old FPL conveying device for conveying the partially conditioned formation protection layer from the first FPL conditioning unit to the second FPL conditioning unit, - a conveying line for conveying a liquid conditioning fluid from a fluid tank unit to the mixing device, - an FPL introduction device for introducing the new formation protection layer, - a ballast introduction device for introducing a new ballast layer onto the intermediate layer, - wherein the FPL conditioning unit comprises a screening device for screening out coarse constituents from the excavated formation protection layer, - a crusher for crushing the screened-out coarse constituents of the excavated formation protection layer, - a coarse particle conveying device for conveying the screened-out coarse constituents of the excavated formation protection layer from the screening device to the crusher, and - a fine particle conveying device for conveying the crushed coarse constituents from the crusher and the screened fine fractions from the screening device to the mixer, - a mixing control unit, - a first connecting line (73 a, b) which connects a fluid reservoir for a conditioning binder fluid to the mixing control unit, - a second connecting line which connects a water reservoir to the mixing control unit,