An engagement head for engaging a porous substrate includes at least two pin sets, each pin set including a plurality of pins arranged in a plurality of parallel pin rows at a predetermined pin angle, wherein pins of immediately neighboring pin rows are arranged such that pin angles for the pins in a pin row are inversely symmetrical to pin angles for the pins in a neighboring pin row. The pins of a pin row move collectively in the same direction when a pin set is extended, which direction is determined by the pin angle of the pin row, whereby neighboring pin rows move in opposite longitudinal directions from one another when the pin set is extended. The pin sets may be extended and retracted in unison by a single actuation source.