Abstract: The proposed device comprises a treatment unit (30) substantially made up of a feed guide (6) for the board and one or more rotating brushes (5) having their axes of rotation perpendicular to the board; this unit is followed by a flip-over assembly (31) and then by a second treatment unit (30) identical to the first. The treatment liquid reaches the center of each brush (5) through a duct. The brush assembly moves transversely; in addition each brush can have an orbital movement. The flip-over assembly (31) consists of a series of facing drive roller pairs (34) mounted on a carriage (32) that can be rotated at 180.degree. around an axis (33). These rollers (34) are such that they can rotate in two different directions.