2008 Twisters on Track to Blow Away Past Records

Recently both the Chicago Sun-Times and the Chicago Tribune reported that 2008 is the deadliest year for tornadoes since 1998. As of the beginning of June, at least 110 people had already died in tornadoes. The Sun-Times also reported that the National Weather Service estimates that 2008 seems on track to break the record for the number of twisters in one year.

The past few days reminded us that the season is not finished but remains quite active. Parts of Wisconsin, Indiana, and Illinois were all hit by weekend tornadoes and related flooding. What have we learned about the way we build and can we do anything to make this situation better?

Concrete and masonry homes have a proven record of good performance in high winds. The solid construction is strong to resist the buffeting forces and its weight is a benefit against uplift that can harm lighter systems. This results in lives saved and property value conserved. If repairs are needed, they are generally completed faster and with less effort. For new construction and rebuilding in tornado-prone areas, concrete and concrete masonry make sense. More on high wind events.

Retempering

Anyone who has worked with mortar knows how it dries out on a board. Summer’s heat and winds accelerate the drying effect. Retempering, the practice of adding water to mortar to restore workability, is considered good practice because it keeps mortar in the right condition for laying brick, block, and stone.

Retempering is done on the mortar board by the mason, usually by dribbling water into the mortar pile, then reworking with a trowel or shovel. This replaces water lost by evaporation. It keeps the mortar plastic so that units can be laid and positioned in it. More on retempering.

Q: What is the purpose of joint reinforcement in masonry walls?

A: In the April 2008 issue of this newsletter, we showed a drawing with eye-and-pintle ties on a two-wythe wall. These two-piece tie assemblies are designed to connect one wythe to the other while allowing for some adjustment for joints that do not align at the exact same height. A brick expert who read the item, John Bufford of Acme Brick, sent a comment suggesting that the use of continuous wire reinforcement and anchors was a far more common tie detail as it serves the dual function of connecting the two wythes together while simultaneously providing longitudinal reinforcement in the concrete masonry backup system for crack control purposes. On further investigation with Jason Thompson of the National Concrete Masonry Association, we agreed that the unit ties originally shown, which do not have longitudinal reinforcement as part of the tie assembly, are not an effective means of providing crack control measures for the concrete masonry wall backup.

To accommodate shrinkage due to temperature or moisture fluctuations, or to account for differential movement between different portions of a wall assembly, concrete masonry walls need longitudinal reinforcement, either in the form of joint reinforcement or bond beams, to minimize the potential for cracking in the wall assembly. When bed joint reinforcement is used, it is frequently placed in every other course. In the case of the original detail, assuming bond beam reinforcement was not used, it would have been appropriate to illustrate the use of a tie assembly that included bed joint reinforcement along with the double pintle and hook system to attach brick veneer. More on joint reinforcement.

ASTM C140 Standard on CMU Reorganized

The Standard Test Methods for Sampling and Testing Concrete Masonry Units and Related Units, ASTM C140, was reorganized late in 2007 and published in January 2008. Designers and specifiers should be familiar with this document, as it is used for evaluating characteristics of concrete masonry units and related concrete units. The big change in this version from previous ones is that annexes were added to address each type of masonry unit, outlining the appropriate test procedures for that type of unit. More on ASTM C140.

Architect Magazine Profiles Brick Plant

The May 2008 issue of Architect takes a look at how clay brick are manufactured. Authors note that brick are “beautiful, …plastic, …and last practically forever.” Like block, brick are often manufactured and used locally, which along with their durability, makes them a sustainable building material.

Although brick’s history dates back to at least 7000 B.C., today’s manufacturing methods are very similar to those used starting around 3000 B.C., when firing became a popular manufacturing method. Made from a basic recipe of shale, clay, and water, today’s brick differs from their predecessors primarily in terms of the speed and efficiency of firing. More on the brick plant.

What are appropriate sheathing materials for plaster construction?

A: Rigid sheathing materials are commonly used behind plaster finishes. They are directly attached to support studs then covered with building paper or other weather resistant barrier (WRB). Metal lath attached over the sheathing and into the supports carries the plaster. The WRB is intended to resist water penetration, so the sheathing is protected from moisture. That means that many materials are suitable for this application, but the common ones remain plywood, oriented strand board (OSB), cement board, and exterior grade gypsum sheathing. More on sheathing materials.

More stucco FAQs.

ASTM Masonry Symposium and Call for Papers

ASTM Committees C01 on cement, C07 on lime, C12 on mortars and grouts, and C15 on manufactured units have announced the next joint Masonry Symposium, to be held in St. Louis in June 2010. The initial call for papers was made in March 2008 to allow interested parties adequate time to submit an abstract. Click on ASTM 2010 Masonry Symposium for more information.

PCA Supports Federal Officials Hardscape Seminar

John Sullivan, PCA’s director, federal infrastructure markets, presented a session on reflectivity of pavements to a group of nearly 60 specifiers from the federal government on May 21, 2008. The presentation, “Solar Reflectivity: A Bright Spot in the Built Environment,” addressed the role of concrete in lessening heat gain in urban settings. The presentation overviewed past efforts to create “cool communities,” current work with urban heat islands, and looked toward the future of the movement. Sullivan referenced PCA reports as technical resources for those interested in learning more about lighting studies, energy savings, solar reflectivity/reflectance, and various other related topics.

Masonry in The Americas

MiTA brought together masonry industry representatives from Canada, Costa Rica, El Salvador, Guatemala, Mexico, Peru, and the United States. The day-and-a-half long program allowed for participants from the different countries of the Americas to discuss the approaches used for structural design of masonry; to discuss the procedures used to develop structural design codes for masonry; to strengthen relationships on codes and standards issues that affect masonry design and construction; and to make the MSJC Code and Specification as useful as possible to code-development experts. This type of information exchange is intended to result in better, safer, more efficient masonry construction in all countries.

The workshop was hosted and sponsored by The Masonry Society with support from the American Concrete Institute, Brick Industry Association, National Concrete Masonry Association, and Portland Cement Association.