Author Archives: CS Editor

Waterproofing for CMUs: What About Stucco?

In the July 2014 issue of The Construction Specifier, we published the article, “Durable Waterproofing for Concrete Masonry Walls: Redundancy Required,” by Robert M. Chamra, EIT and Beth Anne Feero. A month later, we received the following e-mail from G. Michael Starks, president of the Florida Lath & Plaster Bureau (FLAPB):

I thought this article offers sage advice should your plans call for struck and painted concrete masonry unit (CMU) walls. Unfortunately, the predominance of walls today are not struck and painted, but rather have some other exterior finish applied, such as stucco. In this case, recommending a waterproofing admixture or surface sealer without the caveat that doing so will greatly impair the bond of the stucco to the wall is a bit disingenuous. Applying sealers to the CMU prior to plastering requires further bond augmentation where stucco is specified.

The bond of the stucco to the CMU is achieved by the concrete masonry absorbing the water from the fresh stucco. This absorbed water carries the cement paste into the voids in the CMU (a process commonly known as ‘wetting out’), where it cures and locks the two together. Sealing the CMU before stucco application renders this process null, and results in the future debonding of the stucco from the CMU.

ASTM C926, Standard Specification for Application of Portland Cement-based Plaster, includes a Section 5.2, which discusses remedies when bond cannot be achieved over solid bases. Sealing the CMU voids all but one of the possible augmentation procedures and leaves only the last resort of applying a lath and accessories system to the CMU. As stated in C926:

5.2.3. Where bond cannot be obtained by one or more of the methods in 5.2.2, a furred or self-furring metal plaster base shall be installed in accordance with Specification C1063.

In effect, the other six recommendations required before lathing is approved are disregarded by the recommendations provided in the article. The seven means by which to achieve bond provided in ASTM C926 are listed in decreasing order of effectiveness. As such, there is intent for the application of lath to be last in that order. The addition of lath and accessories creates a huge differential in movement characteristics resulting in much higher cracking potential.

Additionally, the installation of lath over a solid substrate, such as CMU or concrete, introduces another challenge in the anchorage and fastening system required to attach the lath and accessories. Finally, from an economic standpoint, stucco applied over lath systems costs three to four times that of stucco direct-applied to the CMU.

Testing performed by the National Concrete Masonry Association (NCMA) indicates the stucco renders the wall as waterproof as (if not more than) those where admixtures and sealers are applied.

Early in this article, there is a statement about shrinkage cracks that occur in unit masonry. These are a result of the same absorption process discussed earlier though with the mortar and CMU. Many of these can easily be prevented by specifying a leaner mortar, such as Type N. In the circumstance where a cement-rich Type M or Type S mortar is specified, proper masonry workmanship can also mitigate the shrinkage effects, such as requiring the masons to fog their walls after initial set and prior to leaving the site in the afternoon much as the plasterers are required to do (ASTM C926) for the stucco. This process averts rapid water loss (volume) during the hydration process, thus minimizing the propensity for shrinkage crack formation.

In conclusion, if you want to waterproof your CMU and you plan to stucco it—seal the stucco, not the CMU. This at least puts the waterproofing on the positive pressure side of the wall.

One of the article’s co-authors— Mr. Chamra—reached out to Mr. Starks, and allowed us to share his response here.

We appreciate the feedback; we concur with your recommendations with stucco applied over CMU. Our article focused on CMU walls because single-wythe without stucco is used in Texas, and there is a lack of knowledge on how to treat them. There is more knowledge on how to waterproof stucco, but this was outside the scope of this article. We also did not discuss other finishes over CMU for the same reason—that topic could be another article in and of itself. Your letter is a good clarifier if our intention was not clear within the article. Thank you for your time and feedback.

Sustainable drinking water treatment systems standard released

A new standard will indicate environmentally responsible drinking water filters based on the lifecycles of products. Photo © BigStockPhoto/trans961

A new standard will indicate environmentally responsible drinking water filters based on the complete lifecycle of products. Photo © BigStockPhoto/trans961

The Water Quality Association (WQA) and the American Society of Plumbing Engineers (ASPE) have announced WQA/ASPE/ANSI S-803, Sustainable Drinking Water Treatment Systems, has been recognized by American National Standards Institute (ANSI) and as an American National Standard.

This standard will help consumers to identity environmentally responsible drinking water filters, and it is now the first sustainability standard for drinking water treatment products to receive the accreditation. The standard evaluates products in all phases of its lifecycle—from material sourcing, to packaging and use, and to the end of its useful life.

Operating on a points-based system, the standard gives manufacturers the choice of meeting various sustainable criteria. As a result, the initiatives having the biggest impact on the specific product or business model can be selected.

Before WQA/ASPE/ANSI S-803 received its accreditation, the original WQA standard underwent public review, as well as feedback from those companies already certified under the standard.

The products included in the standard all employ active carbon, in additional to similar filters made from polypropylene, polyethylene, or string fibers. Moving forward, the scope of WQA/ASPE/ANSI S-803 is set to be expanded to include add-on module for ultraviolet (UV) treatment systems, and dispensers or coolers. Next year, reverse osmosis (RO) and softeners/ion exchange media will be added to the list. Finally, the companion standard, S-803, WQA/ASPE S-802, Sustainable Activated Carbon for Drinking Water Treatment, is in the final stages of the accreditation process.

New ASTM standard for steel announced

A new ASTM standard outlining characteristics of steel reinforcing bars, zinc-coated (galvanized) by hot-dip process in cut lengths or coils. Photo © BigStockPhoto/Igor Stevanovic

A new ASTM standard outlining characteristics of steel reinforcing bars, zinc-coated (galvanized) by hot-dip process in cut lengths or coils. Photo © BigStockPhoto/Igor Stevanovic

A newly proposed ASTM International standard will cover the protection of zinc-coated steel bars used in large infrastructure projects for concrete reinforcement.

ASTM WK46112, Specification for Zinc-coated (Continuous Hot-dip Galvanized) Steel Bars for Concrete Reinforcement, is intended to provide a high-performance, low-cost option for concrete structure protection. The standard will also describe the characteristics of steel reinforcing bars, zinc-coated (galvanized) by the continuous hot-dip process in cut lengths or coils.

“Galvanizing is a proven and effective way to protect reinforcing bars from corrosion as it provides both barrier and galvanic protection to the steel substrate,” said ASTM member Gary Dallin. “It also increases the chloride threshold of steel reinforcing bars. A process to continuously galvanize reinforcing bars (CGR) at a significant cost savings compared to other corrosion-resistant reinforcing bar systems is now operating in two locations.”

Further, using a small amount of aluminum in a zinc bath, the process produces an almost pure zinc coating that adheres well and is resistant to corrosion in concrete.

“With no thick zinc-iron alloy layers, the coated bar can be bent, stretched, or twisted without cracking or flaking the coating, regardless of the total coating mass,” continued Dallin. “As a result, there is no zinc loss due to brittleness during forming in the field and repair requirements are minimal.”

The process allows all grades of steel to be galvanized without changing the mechanical properties.

ASTM WK46112 is being developed by Subcommittee A01.05 on Steel Reinforcement, part of ASTM International Committee A01 on Steel, Stainless Steel, and Related Alloys.

Landscape design guide released

The American Society of Landscape Architects (ASLA) 2012 General Design Award of Excellence was given to “A Green Sponge for a Water-Resilient City: Qunli Stormwater Park” in Haerbin City, Heilongjiang Province, China. The association has released a guide examining benefits of green design features. Image courtesy ASLA

The American Society of Landscape Architects (ASLA) 2012 General Design Award of Excellence was given to “A Green Sponge for a Water-Resilient City: Qunli Stormwater Park” in Haerbin City, Heilongjiang Province, China. The association has released a guide examining benefits of green design features. Image courtesy ASLA

The American Society of Landscape Architects (ASLA) has released an online guide that examines the benefits of green infrastructure and design.

The applications included are green streets, parks, urban forests, wildlife habitat, and vegetated walls or roofs. Communities can benefit from green infrastructure by managing stormwater and reducing flooding and mitigating the heat island effect.

This resource will also provide information regarding the cost-effective aspects of green infrastructure compared to traditional concrete assemblies.

“At all scales, green infrastructure provides real ecological, economic, and social benefits,” said the group’s executive vice president and CEO, Nancy Somerville. “Cities need as much green infrastructure as possible, and landscape architects are implementing it in communities across the country.”

The online resource is part of the organization’s new series of guides and toolkits and includes numerous studies and articles in regards to innovative uses of green infrastructure from large scale to small scale. Additionally, sections are included touching on forests and nature preserves, cities, and constructed wetlands. This information will be useful to landscape architects create these types of systems.

The benefits design professionals and specifiers will learn about green infrastructure include:
● absorption and sequestering of atmospheric carbon dioxide (CO2);
● filtering air and water pollutants;
● stabilizing soil to prevent or reduce erosion; and
● reduce energy consumption through passive heating and cooling.

As the guide is a ‘living document,’ users are encouraged to submit case studies or articles regarding green infrastructure. Click here to access the guide.

New Arkansas Music Pavilion Opens on a Good Note

This photo shows a view of the Arkansas Music Pavilion at night. The polytetrafluoroethylene (PTFE) cone structures come to life with lighting, while at the same time protect concert attendees. Photos courtesy Birdair

This photo shows a view of the Arkansas Music Pavilion at night. The polytetrafluoroethylene (PTFE) cone structures come to life with lighting, while at the same time protect concert attendees. Photos courtesy Birdair

by Doug Radcliffe

Walton Arts Center (WAC) purchased the Arkansas Music Pavilion (AMP) in February 2011 with the goal of expanding the venue to serve a broader and more diverse audience. The AMP operated at the Washington County Fairgrounds after moving from the Northwest Arkansas (NWA) Mall in 2012. However, after seeing a 200 percent increase in ticket sales in 2012, it was clear a permanent site was required to meet the region’s growing need for arts and entertainment. Further, the lack of a roof meant numerous event cancellations due to weather.

In 2013, the Walton Arts Center council approved plans to build a mid-sized, permanent outdoor amphitheater to attract headlining artists and bigger audiences to Northwest Arkansas. As part of a multi-campus expansion in the region, the new Pinnacle Hills venue serves as a major stop for touring concerts in the mid-south.

The new location, in the city of Rogers, has everything WAC was looking for in a permanent venue, including proximity to a major freeway, multiple access points, ample parking, and a supporting infrastructure. This improvement, as well as the 519-m2 (5590-sf) stage, upgraded technical capacities, an artist lounge, and production offices, is expected to attract bigger acts to the venue. The new AMP will also draw in larger crowds with its seating capacity of more than 6000 people, parking, upgraded concessions, and air-conditioned restrooms.

A look up at the three PTFE cone structures supported by steel.

A look up at the three PTFE cone structures supported by steel.

An orchestrated effort
Architecture firm CORE, Tatum-Smith Engineers, general contract consultant David Swain, and Crossland Construction worked to complete this project. A tent-like, weather-resistant covering for the stage was specified. The three-cone and four-inverted-cone-shaped structure is made of a fabric polytetrafluoroethylene (PTFE) fiberglass membrane, with steel supports. PTFE coats a woven fiberglass to form a durable, weather-resistant membrane.

Raising the roof
The AMP’s three-cone shaped structure creates an open, inviting space. PTFE fiberglass membranes can be used to construct roofs, façades, freestanding buildings, skylights, or accent enclosures.

Fabric roof forms are curved between supporting elements in a manner reflective of the flow of tension forces within the membrane. With the exception of air-supported structures, these curvatures are anticlastic in nature. The curving forms of fabric roofs have dramatic appeal. Another attractive feature of tensioned fabric structures is the enormous range of spanning capability. The aesthetic features and the long-span ability of fabric are particularly appropriate for entertainment facilities like the AMP.

Fabric structures are not only visually appealing, but also environmentally responsible and economically competitive. PTFE fiberglass membrane is Energy Star and Cool Roof Rating Council (CRRC)-certified. PTFE fiberglass membranes reflect as much as 73 percent of the sun’s energy, and certain grades of PTFE membrane can absorb 14 percent of the sun’s energy while allowing 13 percent of natural daylight and seven percent of re-radiated energy (solar heat) to transmit through.

The lightweight membrane also provides a cost-effective solution requiring less structural steel to support the roof or façade, enabling long spans of column-free space. Additionally, the tensile membrane offers building owners reduced construction costs and maintenance costs compared to traditional building materials.

DCRDoug Radcliffe has more than 28 years’ experience in steel, glass, and membrane manufacturing, project management, engineering, and construction business. During his career, he has been an integral member of design-build teams for high-profile construction projects of all sizes. Radcliffe is a tensile architectural systems expert at Birdair. He can be reached at sales@birdair.com.