Spotlight: Vertical Rebar Positioners
By Mike Ripley
Vertical rebar positioners have been part of the masonry accessory package for many years. They add no structural value to the wall, but aid the mason contractor in centering the bars in the core of the block and also help to simplify the lapping process.
The most popular and economical positioners for vertical applications are the Figure 8 or S type and the O ring. They are installed perpendicular to the plane of the block crossing the core with the wire loops centered. Positioners are set in the mortar of the bed joint for stability and vertical spacing is about every four feet.
Placement tolerances for single rebar applications are listed in Specification for Masonry Structures (TMS 602-08/ACI 530.1-08/ASCE 6-08) under Part 3 – Execution 3.4 B.8. Working from the center point of the core you are allowed + ½ inch in the width or thickness of the wall and 2 inches along the length of the wall. This leaves you a space in the core center of 1 inch wide by 4 inches long to be code compliant for vertical applications.
Some masons install bars manually (by sight) and others with the aid of positioners but all with the risk of not meeting code. While the use of rebar positioners greatly narrows the margin of error, they also move during installation due to sitting on top of the shelf of the CMU and moving when mortar or the next course is applied.
A new trend in vertical rebar positioners has emerged to solve the movement issue during installation. Core inserted positioners, which are designed to fit 1½-inch deep, cross the core diagonally and fit tightly in the corners of the core. The core positioners perfectly position the bars in the code compliance zone and allow no movement during installation. They also have an extended tail section (safety bend) so if installed incorrectly (out of plane), the tail will extend outside the wall alerting the mason to turn it in the opposite position.
Double vertical core positioners are also available but with a different design, spacing the loops or guides closer to the face shell of the CMU. To complete the family there is a bond beam positioner that positions bars in the lower one-third of the unit and ½-inch off the inside face shell.
Take the guesswork out of rebar placement by using the core inserted positioners.
Mike Ripley is national sales manager for Wire-Bond.