Lath assembly for a sidewall finishing of a floor or ceiling comprising - a combination of at least a first and a second lath (10,20), in which each lath comprises a longitudinal body (11,21) defining a longitudinal direction, wherein the longitudinal body has a first end (12,22) having a first end face (12A,22A), wherein the first end is provided with a keyway (13,23) forming a female part, wherein the keyway (13,23) has a keyway opening (13B,23B) at the first end face (12A,22A); and - a connector for connecting the first ends (12,22) of the pair of laths (10,20) to each other, wherein the connector comprises two key members (31,32) forming two male parts to be inserted into the respective keyway (13,23) of the laths (10,20) to be connected, such that the key member (31,32) extends through the keyway opening (13B,23B), characterised in that each keyway (13,23) of the pair of laths comprises a lath stopper (14,24) comprising an elongated wall portion (14A, 24A), in particular provided by a slit in the keyway, which wall portion (14A, 24A) extends in a transversal direction with respect to the longitudinal direction of the lath, wherein the lath stopper (14,24) is integrally formed with the lath (10,20), wherein the lath stopper (14,24) is arranged for a cooperation with a key stopper (37,38) of the connector wherein each key member (31,32) of the connector comprises a key stopper (37,38), wherein the key stopper (37,38) is integrally formed with the key member (31,32), the key member (31,32) of the connector comprises a plate body, wherein the plate body defines a plane, wherein the key stopper (37,38) comprises a protrusion which extends in a direction away from the plane, wherein the longitudinal body (11, 21) has a front, back, top and bottom side (111,112,113,114) along a longitudinal axis, which longitudinal axis extend in the longitudinal direction, wherein the keyway (13,23) of the lath has a receiving opening (13A,23A) which is provided at the bottom side of the lath to receive the key stopper from beneath into the lath stopper, such that the connector is to be inserted into the receiving opening (13A,23A) in a transversal direction with respect to the longitudinal direction of the lath (10,20), wherein the key stopper (37,38) is in an assembled condition of the lath assembly in a form closure with the lath stopper (14,24) to lock the connector in the longitudinal direction to the lath (10, 20). - a combination of at least a first and a second lath (10,20), in which each lath comprises a longitudinal body (11,21) defining a longitudinal direction, wherein the longitudinal body has a first end (12,22) having a first end face (12A,22A), wherein the first end is provided with a keyway (13,23) forming a female part, wherein the keyway (13,23) has a keyway opening (13B,23B) at the first end face (12A,22A); and - a connector for connecting the first ends (12,22) of the pair of laths (10,20) to each other, wherein the connector comprises two key members (31,32) forming two male parts to be inserted into the respective keyway (13,23) of the laths (10,20) to be connected, such that the key member (31,32) extends through the keyway opening (13B,23B),