Abstract: The spacer 1 defines a body (2) having two opposed sides (3) and (4). The body (2) defines a separation distance between the opposed sides (3) and (4) for use as a spacer intermediate at least two concrete containment panels (5) and (6). Various preferred embodiments have separation distances suitable for forming walls having concrete thicknesses of 50 mm, 120 mm or 150 mm, for example. Each of the opposed sides (3) and (4) include fastening means (7) and (8) adapted for fastening of a cladding panel (16) disposed external to the concrete containment panels (5) and (6), as shown for example in FIGS. (32) and (33). To counter bulging of the concrete containment panels (5) due to the weight of the concrete a brace (49) adapted for fastening engagement with the spacers (1) may be used, as shown in FIGS. (50) to (55). The brace 49 includes an abutment member (50) for abutment with the concrete containment panels (5).