Technical Topic #1

Pain in the Joints?

Does your masonry construction meet project specifications? Does it meet the American Concrete Institute’s (ACI) 530.1? Chances are, you do not know for sure. On most projects, the punch list comes down to “Does it look good?” As materials engineers, River Valley Testing Corp (RVT) tries to avoid the “eye of the beholder” standard for compliance. At RVT, we try to have objective specifications by putting a number on whether the construction passes or fails. To do this, we recommend following, and expanding on, the guidelines in “Specification for Masonry Structures,” ACI 530.1/ASCE 6/TMS 602. In this article, we will refer to this standard as ACI 530.1.

ACI 530.1 covers the quality assurance of grouts and mortars, when the structure can receive structural loads, the protection of the masonry construction during cold and hot weather, reinforcing steel, variation from plumb, joint levelness, joint thickness, and more. This article focuses on joint thickness and an unspecified property, “planeness” of the block face.

ACI 530.1 Section 3.3B sets out a basic joint thickness of 3/8”, “unless otherwise required.” Further, Section 3.3G indicates the allowable tolerance to this basic joint thicknesses; bed joints have a tolerance of +/- 1/8”, head and collar joints have a tolerance of –1/4” to +3/8”. With this tolerance, we can fail the “Does it look good?” question, yet meet the specifications. The reason lies in that ACI 530.1 does not indicate a horizontal or vertical distance in which this tolerance must be met. For example, the head joint on one of an individual block could be 1/8” wide, while at the other end of the block the joint could be 3/4” wide. The same could be true, to a lesser degree, for the bed joints too. The joint variations most often fail aesthetics because the depth of tooling varies, thus creating a non-uniform looking masonry wall. This is especially true where room lighting is located near, or on the wall. A lighting source near joints, with variable tooled depths, will cast noticeable shadows. To reduce this aesthetic concern, RVT recommends inserting a distance component to the joint thickness tolerance. One local firm has successfully specified a tolerance for joint thickness variations as 1/8" in three feet for any similar joint. One could tighten this further to compare to any joint within three feet. Of course, another option would be to move lighting away from the wall. We have found that lighting at least six inches from the wall will not cast many shadows in the joints.

Another area of aesthetic concern lies in how closely the face of the block falls into a plane. When the block is out of plane by as little as 1/16”, certain lighting conditions can make a job look terrible. Unfortunately, ACI 530.1 does not have a variation from plane specification. Where lighting is within six inches of the wall, RVT recommends a block to block tolerance in the project specifications. One local firm specifies a maximum “out of plane” of 1/16” when evaluating adjacent units. They also specify a maximum out of plane of 1/4" in a 10' length of wall and 1/2" in a 20' length of wall. RVT has seen how these few tolerances have allowed the designer to move from “Does it look good?” to “Does it meet the specification?”

George E. Barker, P.E.

Vice President

River Valley Testing Corp