Keeping Water Out with Single-Wythe Walls

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1 Atkinson-Noland & Associates, Inc. Consulting Engineers 2619 Spruce Street Boulder, CO (303) FAX (303) Keeping Water Out with Single-Wythe Walls By Donald W. Harvey, Jr., P.E. Background Since the first publication of Building Code Requirements for Concrete Masonry by ACI Committee 531 in 1978, describing working stress structural design of masonry, relatively slender reinforced concrete block walls have emerged as a popular, economic, and reliable exterior wall system (Drysdale and Hamid 2008). Single-wythe concrete block construction has emerged as a competitor to tilt-up and precast concrete wall panels, especially in warehouse and light industrial construction where an effort is usually made to minimize exterior envelope cost. In recent years, single-wythe concrete block has become a relatively common system in retail and big box construction, especially as integrally colored, split faced block units have become more common. With the use of single-wythe construction in retail applications, the practice of applying interior finishes such as insulation and gypsum wallboard to the interior surface of the single-wythe block assembly has become more common. With limitations on public funding and often overwhelming demands on public space, the use of single-wythe block construction has even extended into institutional construction, again often incorporating interior finishes. The broader use of single-wythe concrete block construction has taken advantage of the economy and aesthetic qualities of modern concrete block. However, the long-term weather resistance of the single-wythe system in these new applications does not have the established track record of masonry cavity wall veneer systems and similar redundant exterior envelope systems. Cases have emerged where interior wallboard finishes have been damaged by moisture infiltrating through exterior single-wythe concrete block walls or where exposed interior block surfaces have shown dampness and efflorescence associated with moisture infiltration. While limited moisture infiltration through single-wythe concrete block systems is not an entirely new or unexpected phenomenon, the consequences of moisture infiltration have changed as the system has moved into retail and institutional settings. What was hardly noticed in a warehouse may no longer be acceptable in a library or courthouse. So can single-wythe construction be safely used in these applications? What about using lightweight block with porous aggregate? If so, what must be done to ensure acceptable weather resistance? While far from a comprehensive study of single-wythe block weather resistance, the research presented in this article begins to address these questions. Purpose of Testing Testing was sponsored by the Rocky Mountain Masonry Institute (RMMI), Basalite Concrete Products, LLC., Boral Best Block, JVS Masonry, Inc., and Texas Industries, Inc. (TXI). The specific purpose of the testing presented in this article was to determine

2 whether or not a single-wythe concrete block wall could provide acceptable weather resistance for retail and institutional applications using common materials and practices. Furthermore, the objective of the testing was to evaluate performance of a system that does not forsake the essential benefits of the modern single-wythe block system: economy and aesthetics. Specifically, the test included lightweight concrete block, which is the most common and economical type of block in the local (Colorado) market. The test was intended to represent the types of materials and construction methods that would commonly be used for applications in the local market. A summary of the masonry material properties used in the study is provided in Table 1. It is understood that local aggregate, materials, and methods will vary significantly in different regions of the country (and world). We encourage similar testing using other regional materials. In fact, as the practice of mockup construction and water testing becomes more prevalent for window, door, balcony, and flashing construction, it is not unreasonable to consider preconstruction water testing of single-wythe wall systems on a project-by-project basis where moisture infiltration at the single-wythe system is of high importance, due to inherent variability in units, geometry, construction practice, integral water repellants, and surface-applied penetrating water repellants. Table 1. Masonry material properties for tested wall. Property Concrete Block Density Concrete Block Coarse Aggregate Mortar Type (per ASTM C270) Mortar Cement Type Mortar Batching Method Value pcf (lightweight) Pumice, Scoria, and Expanded Shale Type S Portland Cement Pre-Blended, Performance Specification Test Setup The test panel described in this article was constructed using ungrouted standard modular ( nominal) lightweight split faced concrete block. The block aggregate was specifically chosen as a worst case scenario for moisture penetration, including expanded shale, scoria, and pumice lightweight aggregate. Both the block and mortar contained an integral water repellant (IWR). The panel was constructed and tested in accordance with ASTM E514, Standard Test Method for Water Penetration and Leakage Through Masonry. A photograph of the subject wall is shown in Figure 2 and the test setup is shown in Figure 3. This test involves the wetting of a 4 foot by 3 foot area while pressurizing the outside surface using a chamber to simulate wind pressure. The test is very severe, simulating a 62.5 mph wind and sheeting rain (3.4 gal/ft 2 /h) for at least four hours, and it is generally understood to provide a benchmark for performance under more Keeping Water Out with Single-Wythe Walls 2

3 severe conditions than an installed assembly is ever likely to experience. The ASTM E514 test is designed to determine two different rates of moisture infiltration: moisture that reaches the interior face of the wall (R i ) and moisture that is collected by the hollow CMU cells but doesn t reach the interior wall surface (R c ). Additionally, we recorded the rate of all moisture infiltration past the surface of the wall, including both of the items above plus moisture absorbed by the masonry units (R s ). The R s value can be compared to results of the field adaptation of this test, ASTM C1601, if both are performed using the same parameters and water penetrating past the face of the block is recorded in the laboratory test. Testing of the panel was performed at three times during the construction process: 1. Approximately 28 days after the block was laid, prior to cleaning of the wall. 2. After the wall had been cleaned using aggressive power washing with a high-pressure nozzle with the tip within 1 foot of the masonry surface. 3. After the application of an RTV silicone penetrating water repellant. It should be noted that the tested panel did not have significant visible debonding or cracking at mortar joints. It has been our experience that early drying shrinkage of mortar resulting in separation of the mortar from the adjacent unit can dramatically increase moisture penetration through single-wythe block walls. An attempt to understand the causes of this type of debonding is the subject of a separate research project in cooperation with Dr. Jennifer Tanner at the University of Wyoming. Test Results The water resistance of the wall assembly during all three tests was excellent. During all three tests, the amount of water collected from the block cells and the amount of water collected from the interior wall face were not enough to measure (i.e. R i and R c 0). No damp spots or only small damp patches were visible on the interior face of the wall after four hours of testing in every case (Figure 4). There were some changes in the rate of moisture penetration past the wall surface (R s ) for the three tests. The total volume of water penetrating past the wall surface over time for all three tests is shown in Figure 5. The rates of moisture infiltration past the wall surface are summarized in the table below: Table 2. Summary of moisture penetration rates. Time of Test Rate of Moisture Penetration Past Wall Surface, R s (gal/h/ft 2 ) Rate of Moisture Penetration Past Wall Surface, R s (l/min) Prior to Cleaning After Cleaning After PWR Application Keeping Water Out with Single-Wythe Walls 3

4 While all of the rates are very low, the rate of moisture penetration past the wall surface increased slightly after aggressive power washing and decreased to a level below the pre-cleaned condition after installation of the penetrating water repellant. Conclusions In evaluating the test results, a fundamental question emerges: How much is too much? That is, what rates of moisture penetration through the surface, at the cores, and at the interior surface are acceptable? While this would appear to be a relatively simple question, there is little published guidance to help provide an answer. The current version of both ASTM E514 and C1601 provide no guidance regarding acceptable levels of moisture penetration. The 1974 version of ASTM E514 was the last version of the test method that provided a grade or rank based on the moisture penetration rates. However, these rates were not specifically intended for use in single-wythe concrete block walls, and even if single-wythe block walls were considered in the performance classifications, the application of single-wythe concrete block has changed dramatically since The highest grade (E) in this standard requires that no dampness be visible at the interior face of the wall after 24 hours of continuous testing. The relatively new standard for testing cavity drainage, ASTM C1715, lists an expected moisture penetration rate (R i ) of 0.11 gal/h/ft 2 that appears to be based on clay brick masonry veneer construction. However, this penetration rate is clearly associated with a different type of construction (cavity wall). We have anecdotally observed single-wythe concrete block walls with interior finish damage with surface penetration (R s ) rates ranging from 0.24 to 2.40 gal/h/ft 2. We do not have a sufficient range of test conditions to establish an appropriate maximum or range of maximum penetration values based on our experience alone. However, the rates of infiltration on the tested single-wythe wall are roughly two orders of magnitude less than problematic conditions that we have encountered. This is a fairly strong indication that the moisture penetration of the tested single-wythe wall would not cause distress. The principals set forth in the 1974 version of the E514 standard are, in my opinion, the most appropriate way to evaluate the water resistance performance of a single-wythe wall. Dampness and moisture at the interior surface of the wall are the most likely conditions to cause damage or affect appearance. Therefore, observation and measurement of this moisture is most critical. The interior face of the completed singlewythe test wall did not display any damp spots within the test area at the interior face after four hours of testing. Considering the severity of the ASTM E514 test and the high levels of interior moisture we have encountered when testing problematic walls, it is reasonable to conclude that the water penetration through the tested single-wythe wall is Keeping Water Out with Single-Wythe Walls 4

5 negligible. Further, it is reasonable to conclude that a wall of this construction in service would not experience moisture-related distress. One of the important aspects of this single-wythe test program was determining whether weather-resistant performance was feasible using common lightweight aggregates in the block mix. The RMMI recommended practice for moisture-resistant lightweight walls prior to this testing required the block to be Medium Weight or Normal Weight per ASTM C90. These heavier block are not preferred by masons and not common in the Colorado market. The study indicated that lightweight block, even block with relatively porous lightweight aggregate, can be effective in resisting moisture penetration. The use of integral water repellant in the masonry and surface-applied penetrating water repellant made the lightweight block very moisture resistant, even under the very severe E514 test conditions. The E514 test does not include testing of waterproofing details associated with window and door openings, base and bond beam flashing, beam pocket flashing, penetrations, and other potential sources of moisture infiltration. However, this testing illustrates that successful, moisture-resistant single-wythe concrete block walls can be constructed without significant risk of damage to interior finishes. Based on the results of this testing, RMMI updated their recommendations for exterior single-wythe concrete block construction as shown in Figure 6. Keeping Water Out with Single-Wythe Walls 5

6 References Masonry Structures: Behavior and Design, 3 rd Edition, Drysdale R.G. and Hamid A.A., The Masonry Society, Standard Test Method for Water Penetration and Leakage Through Masonry, ASTM Standard C514, 2009, ASTM International, West Conshohocken, PA, 2009, DOI: /C514-09, Standard Test Method for Field Determination of Water Penetration of Masonry Wall Surfaces, ASTM Standard C1601, 2010, ASTM International, West Conshohocken, PA, 2009, DOI: /C , Standard Specification for Loadbearing Concrete Masonry Units, ASTM Standard C90, 2010, ASTM International, West Conshohocken, PA, 2011, DOI: /C90-11a, Standard Test Method for Evaluation of Water Leakage Performance of Masonry Wall Drainage Systems, ASTM Standard C1715, 2010, ASTM International, West Conshohocken, PA, 2009, DOI: /C , Keeping Water Out with Single-Wythe Walls 6

7 Figure 1. View of aesthetically pleasing use of single-wythe concrete masonry construction. Sun MicroSystems Building, Photographer: Jackie Schumacker, Atkinson-Noland & Associates, Inc. Consulting Engineers 2619 Spruce Street Boulder, CO (303) FAX (303)

8 Figure 2. View of single-wythe concrete block wall test specimen prior to testing. Note that the perimeter of the specimen is coated with plaster in accordance with ASTM E514 requirements. Keeping Water Out with Single-Wythe Walls 8

9 Figure 3. View of single-wythe concrete block wall and ASTM E514 test setup. The clear box is pressurized to simulate wind, and the spray bar at the top of the box sprays water onto the block surface to simulate rain. Keeping Water Out with Single-Wythe Walls 9

10 a. b. c. Figure 4. View of the interior surface of the single-wythe concrete block test wall following each test: a. prior to cleaning, b. after cleaning, c. after penetrating water repellant installation. Damp areas (all located at head joints) are circled. Keeping Water Out with Single-Wythe Walls 10

11 Figure 5. Total water penetrating beyond the wall exterior surface and total water penetrating to the interior over time for the three E514 tests. No water was collected at the interior for all three tests. Keeping Water Out with Single-Wythe Walls 11

12 CHECKLIST for SINGLE WYTHE CONSTRUCTION We performed a series of ASTM E-514 tests on some locally-manufactured block that led us to believe that single wythe construction can be effective IF you follow ALL our recommendations. Single wythe construction is not redundant or forgiving. You cannot take any shortcuts. Specifically, we recommend: 1. Use integral water repellent in both the block and in the mortar. The repellent in the mortar should be compatible with the repellent in the block. 2. Apply a breathable spray-applied water repellent on top of the block in addition to the integral water repellent. This product should be chosen to work with the chemistry of the block. 3. Minimize cracking by installing horizontal reinforcing (ladder-style, not truss-style reinforcing) at 16 on center, vertically. 4. Install enough control joints to prevent excessive shrinkage cracking. Follow the guidelines described in NCMA Tek Note 10-2B. 5. Double-butter the head joints so that you get full mortar fill here. 6. Use concave tooling for the mortar joints. Do NOT allow other tooling styles. They are not as water repellent. 7. Make sure that excess water does not get into the building. a. Protect horizontal exposures (parapets, sills, changes in plane) with appropriate flashing. b. Make sure that the grading at the base of the building slopes away from the building. c. If you have gutters and downspouts, make sure that the downspouts discharge the water at least 48 from the building. d. Do not allow scuppers to let water flood down the face of the wall. (Scuppers are OK for overflow drainage only). 8. Assume that water will eventually penetrate your walls. Make plans to flush this moisture harmlessly to the exterior. a. Install flashing and weep holes (or a proprietary weep system) above all bond beams. b. Install flashing and weep holes (or a proprietary weep system) at the base of the wall. c. Make sure you have a change in plane at the base of the building. Do NOT align the exterior sidewalk, the top of the foundation and the first floor level with each other. 9. Install backer rod and sealant where masonry meets metal. These materials move differently with temperature change and you will develop a crack where they join if you use mortar instead of sealant. 10. If you choose to install insulation in your single wythe wall, use rigid insulation NOT batt insulation. You cannot protect the back side of the batts from moisture. You can also install insulation in the ungrouted core holes. 11. Do NOT install vinyl wall paper or other non-breathable wall covering on single wythe walls that are exposed to weather on one side. 12. Clean the walls in a timely manner. Wait at least 7-10 days so the mortar is cured. Do not wait more than 30 days or you will have to be too aggressive in cleaning the wall. Use a chemical to clean the block that is acceptable to the block manufacturer. Do NOT use Muriatic acid. 13. Do NOT clean by sandblasting. Sandblasting opens up tiny hairline cracks and can lead to water intrusion. Figure 6. List of updated single-wythe concrete block wall recommendations from the Rocky Mountain Masonry Institute. Keeping Water Out with Single-Wythe Walls 12