The device (1) to the relaxation of a fabric in a direction of relaxation (z ′ z), the fabric having a cavity comprising a first surface, a second surface and an opening for insertion of the device in the cavity in a longitudinal direction (x ′ x), comprising a base (21) intended to bear on the first surface, a mobile plate (23) intended to bear on the second surface, a spacer element (25) to move the plate to a position of relaxation, an actuator (27) of the spacer to selectively adjust the position of relaxation, and a passage extending along the longitudinal direction to the introduction of a cement in the cavity.
