How thick can the wire in bed joint reinforcement be before it is considered too big to fit in the joint? In most cases, I have seen bed joint reinforcement made from No. 9 wire. On a few projects, I have been asked to use 3/16-inch diameter wire. Can bed joint reinforcement greater than 3/16-inch diameter be used?
The diameter of the bed joint reinforcement must not be greater than half the width of the mortar joint. In most cases, mortar joints are 3/8 inch thick, so the maximum diameter of the bed joint reinforcement is 3/16 inch. Wire greater than this diameter will create problems. Mortar may not adequately cover the bars and the reinforcing may not lie flat, which will tend to lift the units when the mortar is green. This requirement is paragraph 8.2.3 in the 1995 Masonry Standards Joint Committee Code (ACI 530/ASCE 5/TMS 402) or in the 1999 MSJC Code. Even 3/16-diameter wire reinforcing can pose a problem. If the wire is hot-dipped galvanized, it will be thicker than 3/16 inch, making it too thick for a 3/8-inch mortar joint. For most applications, use No. 9 hot-dipped galvanized wire in bed joint reinforcing.