Abstract: The method of impregnating substantial amounts of asphalt into fiberboard. Melted asphalt having desired properties for use with fiberboard is atomized and then chilled by passage through cold water sprays, and into a cellulose-fiber-containing slurry. The asphalt used has a high penetration at elevated temperatures and is atomized at a lower temperature than is ordinarily utilized in producing atomized asphalt. The slurry may then be pumped into a chest, stored therein, pumped into a deculator, and then to a head box and flowed on to the wire screen of a Fourdrinier machine, forming a wet mat. Or, the asphalt-containing slurry may be further asphalt-enriched by spraying atomized asphalt into it as previously, and then pumped into a chest enroute to a Fourdrinier machine. Water drains through the wire screen, and the mat then goes to the dryer. The slurry-handling and the board-forming steps are conventional.