Hook-and-eye is the most is widely accepted product used today for joining a brick wall and block wall together, while simultaneously reinforcing the mortar joints of the block wall. The original idea of welding an eye assembly onto 10-ft wall reinforcement was introduced and patented in the 1960s, and the concept has been tested and improved numerous times in the many years since.
Masons in the early days liked the adjustable capability of the system, which allowed for changes in coursing and absorbed small margins of error between wall heights. There was also a trend to use additional insulation between the walls, and hook and eye was quite compatible with this placement.
The block wall could be constructed, waterproofed, or insulated and the brick wall put up later. With the perimeter of the building constructed, the general contractor was on the fast track, saving considerable time on interior construction. This approach also made it much easier to use colored mortar or accommodate other differences in wall construction techniques.
Once the patent expired, numerous manufacturers began making their own versions. As costs were reduced, it became more widely accepted. Hook-and-eye was installed simply and economically and became the product of choice among masons.
In 1989, the ACI 530 code was written to improve the quality and durability of masonry walls. Specifications for hook-and-eye design were stipulated in section 22.214.171.124.2.
Spacing of the eyes was reduced to 16-in. on-center from the generally accepted 24-in. on-center. This change put a hook-and-eye assembly at every 1.77 sq ft of wall area. The code also stipulated that adjustable ties in cavities must have two 3/16-in. diameter strands to tie walls together.
The code also made tolerances tighter for the size of the eye, and required all exterior wall reinforcement to be constructed from hot dipped galvanized. These requirements improved the quality and longevity of the wall.
New tolerances meant that the brick veneer would not move enough to cause damage in either positive or negative loading. The tighter tolerances for the eye required only 1/16-in. clearance between the hole and hook, and changed the shape of the eye from a teardrop (Fig. 1A) to a lollipop (Fig. 1B).