A device for producing molded concrete blocks includes a mold lower part in which at least one mold cavity is formed and a mold upper part including at least one pressure piece with a lower face facing the mold cavity, an upper face facing away from the mold cavity, and lateral surfaces, wherein the pressure piece has fluid openings on the lower face and/or on the lateral surfaces and is designed to engage into the mold cavity such that when the pressure piece is engaged, a fluid can be introduced into the mold cavity from the fluid openings and/or when the pressure piece is engaged, a fluid can be discharged out of the mold cavity from the fluid openings.

A mold part (6) for manufacturing vertical joints of keystones (5) comprising a foam piece (7); and a silicone piece (11) covering the foam piece (11), wherein the foam piece (7) and the silicone piece comprise a plurality of protrusions (17) and recesses (16), thus providing a toothed surface in a concrete surface of the vertical joint. The mold-part can comprise stiffeners (20) and handles (19, 21) for demolding manually after curing the concrete keystones, leaving the inner surface of the keystone with a toothed appearance.