Q: How frequently should control joints be spaced in unreinforced concrete masonry walls?
A: When no joint reinforcing is used, National Concrete Masonry Association (NCMA) TEK 53, "Design of Concrete Masonry for Crack Control," recommends spacing control joints in straight wall sections without openings no farther apart than twice the height of the wall, 40 feet maximum. Thus, for a 10-foot-high wall, control joints should be placed 20 feet on center. If joint reinforcing is used, the spacing can be increased as shown in the table. Note that the recommendations in the table are for Type I moisture-controlled units. If Type II nonmoisture-controlled units are used, reduce the control joint spacing. In such cases, James Amrhein, in his book, Reinforced Masonry Engineering Handbook for Clay and Concrete Masonry, recommends reducing control joint spacing by as much as one-half.
Control Joint Spacing for Moisture-controlled,
Type I Concrete Masonry Units
Vertical Spacing of Joint Reinforcement None 24
Expressed as ratio of panel length to height (L/H) 2 2 1/2 3 4 With panel length (L) not to exceed (feet) 40 45 50 60
Source: Table 4 from National Concrete Masonry Association TEK 53