When the boxes are installed in ceilings the mounting ears are bent out. If the opening has an applicable size the box just has to be hooked into the opening. If not, a suitable support can be rendered quickly with some wooden slats. The gap can be padded closely with mineral rock wool on the underside and then be poured out with mortar. If the opening is too big it is better to set up the mould from below. In this case the boxes are fixed in the concrete formwork and then are poured in.