Masonry Magazine February 1976 Page. 13
Detail Variations
In addition to differences in shape, other variations exist which involve the number of cores in a unit, unit ends, the face shell (exterior portion) of a unit, or the webs (solid sections between cores).
End flange may be grooved, as shown, or plain.
Face shells and webs increase in thickness from bottom to top. Depending on the core molds used, face shells and webs may be flared, tapered, or straight tapered. A flared face shell provides a wider surface for mortar. Relatively thin face shells and webs are sometimes used in order to hold weight to a minimum. This requires use of a stronger concrete to meet strength requirements. Standard face shell and web thickness for concrete masonry units are shown in table below.
Some manufacturers make either a two or three core unit exclusively; others make some sizes and shapes in both types and others in only one type.
Some manufacturers of three core units thicken the face shell at the center cores, in order to make the unit more resistant to cracking at this point.
Equivalent Solid Thickness
"Equivalent solid thickness" is the average thickness of solid material in the unit, and is used as a criterion of fire resistance. We can compute equivalent solid thickness by means of the following formula. If P, equals percent solid volume, T equals actual width of a unit, and Eq Th equals equivalent solid thickness, then:
Eq Th = T-P/100
Regular stretchers in 8", 10" and 12" widths are generally available with concave ends. Generally all 4" and 6" units are made with plain ends.
Table 3 Properties of Hollow Block with Minimum Face Shell and Web Thickness permitted by ASTM C-90.