such length that when the spacer member 14 is properly positioned the outer surfaces of elements 16 are spaced inwardly of the planes formed by block faces 4 and 6 cross shaped elements 16 are used to provide horizontal space between adjacent blocks 2 in a particular layer of blocks as well as vertical space between adjacent layers of blocks each cross shaped element 16 includes a first set of oppositely directed arms 20 which preferably rest upon horizontal portions of raised side edges 10 and a second set of oppositely directed arms 22 intersecting and extending perpendicularly to arms 20 in order to insure secure anchoring of the spacer member in the mortar as shown in the illustrated embodiment arms 20 assume a channel like configuration while arms 22 take the form of a corrugated or notched configuration however these arm anchoring configurations may be reversed both configurations may be identical or the arms may assume entirely different anchoring configurations or be provided with some other anchoring structure such as through holes for example to enhance interlocking of the mortar with the spacer member in block placement the blocks are brought into abutment with the arms 20 and or 22 such that the width of arms 20 and or 22 defines the outwardly visible width of the joints between the blocks as seen in fig1 5 and 8 the distal ends of arms 22 include inwardly facing tab members 24 having oppositely directed.