Method for molding concrete blocks or bricks

In a method for molding concrete elements in an open top mold having a primary mold cavity defined by walls lined with a thermoplastic film which is first moved onto said open top of said mold, heated and sucked by vacuum into said primary mold cavity which is then filled with a concrete mix for the formation of the element, the improvement comprising the following steps:

• (a) contacting at least that portion of said thermoplastic film which smoothly covers said open top, with a flat heater surface of a solid heating device for uniformly and entirely heating said portion of said thermoplastic film on said open top through said flat heater surface, while simultaneously closing said open top with said solid heating device, said heating softening said film portion sufficiently for pulling the heated film portion into said primary mold cavity by suction,
• (b) evacuating said primary mold cavity while it is still closed by said heating device, sufficiently for lining the primary mold cavity with a secondary mold formed of said thermoplastic film in said primary mold cavity,
• (c) removing the heating device for opening said secondary mold in said primary mold cavity,
• (d) filling the secondary mold in said primary mold cavity with a concrete mix, and
• (e) compacting said concrete mix in said secondary mold while the seconsary mold is still in said primary mold and withdrawing the secondary mold filled with compacted concrete mix from said primary mold cavity prior to any substantially noticeable or effective hardening of said concrete mix in said secondary mold which together with the compacted but not yet effectively hardened concrete mix forms a unit sufficiently shape retaining for an immediate transportation and completing the curing and hardening of the concrete mix in said secondary mold outside said primary mold with the curing concrete mix a sufficiently shape retaining unit so that expansion forces resulting from the hardening and curing are substantially prevented from becoming effective in the primary mold and for permitting the renewed use of said primary mold cavity before the formed concrete mix hardens.