Keeping Water Out with Single-Wythe Walls

Single-wythe concrete block construction takes advantage of the structural and aesthetic qualities of modern concrete block while saving money. Single-wythe construction is now commonly used in retail “big box” construction, institutional facilities, warehouse and light industrial construction in the Rocky Mountain region. In order to confirm that a single-wythe concrete block wall built with common local materials could provide acceptable weather resistance the Rocky Mountain Masonry Institute (RMMI) conducted a series of ASTM E-514 tests to evaluate performance of a lightweight concrete block system. The test represented the types of materials and construction methods that would commonly be used for applications in Colorado. The study indicated that concrete block, even block with relatively porous lightweight aggregate, can be effective in resisting moisture penetration if used with both integral water repellant and appropriate spray-applied water repellant. 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 ASTM E514 test involves the wetting of a 4 foot by 3 foot area of a single-wythe wall while pressurizing the outside surface using a chamber to simulate wind pressure. The block aggregate selected for the text was specifically chosen as a worst case scenario for moisture penetration – the block mix included expanded shale, scoria, and pumice lightweight aggregate. Both the block and mortar contained an integral water repellant (IWR). The E514test is very severe. It simulates a 62.5 mph wind and sheeting rain (3.4 gal/ft2/h) for at least four hours. This test is generally understood to provide a benchmark for performance under more severe conditions than an installed assembly is ever likely to experience. The panel was tested three times: • The first test was conducted approximately 28 days after the block was laid, prior to cleaning of the wall. • The second test was done 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. • The final test was performed after the application of an RTV silicone penetrating water repellant. 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. The Rocky Mountain Masonry Institute recommends using integral water repellant in both the block and in the mortar. The repellant in the mortar should be compatible with the repellant in the block. After construction, apply breathable spray-applied water repellant that works with the chemistry of the block. Additionally, pay attention to proper detailing with control joints, flashing, backer rod and sealant, and install the mortar using double-buttered head joints. The testing was sponsored by Basalite Concrete Products, LLC., Boral Best Block, JVS Masonry, Inc., and Texas Industries, Inc. (TXI). The white paper on the test is available for download at www.rmmi.org