Should I specify Type I moisture-controlled units or Type II nonmoisture-controlled units for exterior concrete masonry walls?
For large structures, most references recommend using Type I moisture-controlled units. In some areas, however, Type I units may be difficult to obtain. Even if Type I units are specified, though, they may not be Type I by the time they're installed in the building. Type I concrete block that are not protected from weather can pick up moisture during storage, changing them to Type II units. Walls built with Type II units are more likely to develop shrinkage cracking than walls built with Type I units. This is especially true if units with high moisture content are used in walls in arid climates. I recommend using Type I units. When Type I units are used, perform random tests on units to verify their moisture content on delivery to the site. The units must be protected onsite so they don't pick up excessive moisture during storage. If Type I units are not available, use Type II units. Use joint reinforcement and reduce the spacing of control joints to as much as one-half of that recommended for Type I units.