Control joint spacing in stucco on block

In stucco on block What are the control joint spacing requirements for stucco on block? "Control joint spacing in masonry is usually between 20’ to 25’ on center.   Joint spacing and location in stucco is dependent on whether the stucco is directly applied to the solid substrate or is placed onto lath which in turn is attached to the wall.

​In the case of directly applied (called “direct applied”) stucco the bond between the stucco and the solid substrate (in this case concrete block) is the most important thing.    With good bond the thin layer of stucco will crack in any place the solid substrate cracks.  Thus, there should be a control joint in the stucco at any location that you find a control joint in the block.   There are no other control joints required in direct applied stucco.

In stucco on lath, the ASTM 1063 code requires a control joint at a maximum spacing in walls of 18 ft o/c both horizontally and vertically enclosing an area no more than 144 sf.  The area enclosed by the control joints cannot have a length to width ratio greater than 2 ½ :1 .  The control joints in the lath are not require to line up with the control joints in the block because in this case the stucco layer is independent of the wall to which it is attached."