e approximately 50 degrees the width of vertical wave divider 60 between its sidewalls 62 is approximately one third of the width of builder block 1 adjacent builder blocks 1 are held together not only by the tongue in groove arrangement fig3 but also by a backplate connector 90 fig4 specifically each builder block 1 is made with an embedded bolt 80 projecting outwardly from the upper rear corner thereof when two blocks are placed adjacent one another as in fig3 a backplate 90 having spaced horizontal slots 91 is put in position over projecting bolts 80 slots 91 are sufficiently long and are located such that slight misalignment between adjacent blocks 1 will not prevent backplate 90 from being placed in position over projecting bolts 80 once plate 90 is in position suitable washers and nuts 81 are threaded over bolts 80 to firmly hold backplate 90 against the rear walls 30 of adjacent builder blocks 1 while the dimensions of builder blocks 1 can vary the dimensions of a block made in accordance with the best mode currently contemplated are based basically on a six by six by five foot block the length of base 10 from front to.