Abstract: A spacer core for use in constructing hollow concrete walls by introducing the core between and spaced from a pair of vertical mold plates before casting the wet concrete, and subsequently removing the spacer core, the lower end of the spacer core including a water permeable wall and a bottom chamber for accumulating water permeating the wall. Also described is a method of constructing hollow concrete walls by the use of the above spacer core by: introducing the spacer core between and spaced from a pair of vertical mold plates; casting wet concrete into the spaces between the spacer core and the mold plates, whereby the water from the concrete permeates through the bottom of the spacer core into the bottom chamber; after a first time interval, lifting the spacer core a first predetermined distance to draw water from the concrete into the bottom chamber; and subsequently removing the spacer core from the concrete.