Abstract: Concrete elements, such as blocks or bricks, are molded or cast by forming in a primary mold cavity a secondary mold made of a portion of a thermoplastic film which has been contacted with a flat heater surface to assure a uniformly heated film portion which is then sucked into the primary mold cavity without wrinkles and filled with concrete mix. The secondary mold with the concrete mix in it is withdrawn, for example, sucked out of the primary mold cavity well before any effective hardening of the concrete mix, so that curing and hardening takes place in the secondary mold outside the primary mold cavity. This early withdrawing is important because it avoids expansion of the curing mix in the primary mold, whereby removal from the primary mold is facilitated. Additionally, the early removal with the aid of the secondary mold assures a more efficient use of the primary molds which are used again while the hardening is still going on in the secondary mold.