Image
Norbert V. Krogstad
Different block

Q: What is the difference between a bond beam block and a lintel block in concrete masonry?

Is it possible to use lintel block over windows and as bond beams within the field of the wall?

A: Bond beam blocks are concrete masonry units that are similar to standard CMUs, except that the webs are cut to remove the upper portion. In many cases, the block units are provided with knock out sections that are removed when the units are used in the bond beam.

The notch in the top of the webs creates a space into which the horizontal reinforcing is placed in a reinforced masonry wall. The vertical reinforcing extends through the cells in the bond beam unit. A wire mesh or fabric is placed in the bed joint just below the bond beam unit at any of the cells that do not contain vertical reinforcing as the walls are erected. This mesh prevents the grout from flowing down the vertical cell space so the horizontal bond beam can be filled without filling all the vertical cells.

Lintel or channel blocks are U-shaped concrete masonry units used above openings to create lintels. Since lintel block units are solid along the bottom, the underside can be exposed at openings. However, because of this feature, these block units do not allow vertical reinforcement to extend through them.

Therefore, lintel blocks would typically not be used in wall systems that have a combination of vertical and horizontal reinforcement. If lintel blocks are used to create bond beams in walls with vertical reinforcing, a portion of the bottom of the units would need to be removed in order to extend the vertical reinforcing through.

Lintel blocks also are often used within bearing walls that do not contain vertical reinforcing below the ends of steel joints. In this application, a steel bearing plate for the bar joists can be embedded in grout.

Cull lesson

Q: I have heard masons refer to broken or defective masonry units as “culls, ” yet I have seen many brick installed in the wall that have small cracks in corners or other defects. Wouldn't these also be “culls?”

If so, who decides which ones are acceptable to put in the wall and which ones are not?

A: A cull is defined as a unit that does not meet the ASTM standard specification requirements. For clay or shale face brick, the standard specification is ASTM C216.

ASTM C216 has several appearance standards that include tolerances for warp-age and chipping of the unit. Regarding chips, ASTM C216 states in Section 8.4 that “The face or faces that will be exposed in place shall be free of chips that exceed the limits given in Table 2.” The size of the permissible chippage at corners and edges depends on the type of brick (FBX, FBS -Plain, FBS - Textured, or FBA), and the percentage of such chips.

The term “Textured” is defined in this table to mean “extruded brick with the face sanded, combed, scratched, scarified, or broken by mechanical means such as wire-cutting or wire-brushing, or molded brick.” “Plain” is defined as “extruded brick with an unbroken natural die finish face.”