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Testing the Test: Water Absorption with RILEM Tubes by Adrian Gerard Saldanha and Doris E. Eichburg All images courtesy Building Diagnostics Inc. WATER REPELLENTS ARE OFTEN APPLIED TO EXTERIOR WALLS TO REDUCE ABSORPTION. A COMMON QUESTION FROM BUILDING OWNERS IS, “WHEN DOES THE REPELLENT NEED TO BE RE-APPLIED?” SINCE WATER REPELLENTS ARE CLEAR, VISUAL INSPECTIONS ARE NOT USEFUL TO EVALUATE THEIR DURABILITY. A SIMPLE FIELD TEST FREQUENTLY USED TO MEASURE THE EFFECTIVENESS OF WATER REPELLENTS IS THE RILEM TUBE. BUT IS THIS WIDELY USED TEST SUFFICIENTLY RELIABLE? 1 The RILEM tube test was adopted in the United States in the early 1980s by the water repellent manufacturing industry to assess water absorption properties of walls and other substrates, with or without treatment. Simply put, the test measures the quantity of water absorbed by a particular substrate over a given time through an uptake tube. The uptake tube is sealed to the substrate with putty (Figure 1). RILEM was an acronym for the original French name of a European organization founded in 1947 to promote scientific co-operation in the area of construction materials and structures. A RILEM technical committee developed “Test No. II.4 Water Absorption Under Low Pressure (Pipe Method)”—now commonly known as the RILEM tube test—and explained its uses in a 1980 report. 2 The hydrostatic head developed by the column of water in the tube can be correlated with wind- driven rain of a certain speed. This relationship is not linear; pressure is proportional to the square of velocity, so the wind speed per 1 ml (0.04 oz) of water at the bottom of the tube is about twice that at the top of the tube. 50 the construction specifier | august 2013 CS_August2013.indd 50 7/17/13 3:00:24 PM