Scouring came first. "In Roman times, fulling was conducted by slaves standing ankle deep in tubs of human urine and cloth. Urine was so important to the fulling business that urine was taxed. Urine, known as 'wash', was a source of ammonium salts and assisted in cleansing and whitening the cloth.
By the medieval period, fuller's earth had been introduced for use in the process. This is a soft clay-like material occurring in nature as an impure hydrous aluminium silicate. This seems to have been used in conjunction with 'wash'. More recently, soap has been used."
Thickening is the second step. "The second function of fulling was to thicken cloth, by matting the fibers together to give it strength and increase waterproofing (felting). This was vital in the case of woollens, made from short staple wool, but not for worsted materials made from long staple wool. After this stage, water was used to rinse out the foul smelling liquor used during cleansing.