Impermeability—Hydrostatic Pressure Resistance

It may seem unnecessary to state, but waterproofing should be impermeable. Waterproofing should stop the passage of liquid water and it should provide that barrier at the hydrostatic pressure present at a particular project.[47] While resistance to hydrostatic pressure is a widely expected characteristic of waterproofing, four of the six material specifications have no requirement for hydrostatic pressure resistance. Refer to Table 1 for a review of standards.

AC29 and CAN/CGSB-37-GP-52M require hydrostatic testing after stressing the membrane test speci­men. AC29 requires that the membrane specimen be stretched by the introduction of a gap in the substrate, which simulates a substrate crack. The CGSB test uses a dynamic impact test, which simulates abuse during construction, followed by a mild hydrostatic test.

The hydrostatic test method in CAN/CGSB SB-37-GP-52M is simple and probably reproducible. The impact test and the water test are conducted in separate operations, which contribute to the simplicity of the test. CAN/CGSB SB-37-GP-52M requires hydrostatic testing with a 500 mm (1.6 ft) column of water, which is the equivalent of the hydrostatic pressure in a shallow planter.

The hydrostatic testing required in AC29 is more demanding, but the standards it references provide little assurance of consistent results when conducted in different laboratories. AC29 allows either of two test methods to be used to measure hydrostatic pressure: ASTM Test Method for Hydrostatic Pressure Resistance of a Liquid-Applied Waterproofing Membrane (ASTM C 1306) and ASTM Test Method for

TABLE 2—Impermeability—Requirements in standards regarding moisture vapor resistance. Values and units are stated in the table as they are expressed in the standards.

Standard_______________________ Requirement____________________ Test Method_____________________

Hydrostatic Pressure Resistance of Waterproofing Membranes (ASTM D 5385.) These standards are modi­fied by AC29; instead of a normal 3.2 mm (1/8 in.) crack opening, a minimum 1.6 mm (1/16 in.) crack opening is allowed. AC29 requires that the materials do not leak when tested at twice the hydrostatic pressure anticipated for a specific building.

In the “Precision and Bias” sections of both standards referenced in AC29, there is an indication that the tests offer less reliability than the writers of AC29 may have desired. ASTM D 5385 makes no statement “concerning either the precision or bias of this test method since the result states merely that the system tested passes this test at a specific pressure and does not leak water for 1 h.”

The subcommittee responsible for ASTM C 1306 organized a round-robin process to evaluate the test method in terms of repeatability (within a laboratory) and reproducibility (between laboratories); however, the results are not encouraging. Regarding reproducibility, ASTM C 1306 concludes that, “In future use of this test method, the difference between two test results obtained in different laboratories on the same material will be expected to exceed 21.082 psi only about 5 % of the time.” A difference of 0.145 MPa (21.082 psi) is a very large variation in test results, considering that the variation is approximately equal to the total hydrostatic pressure on a structure 15 m (49.2 ft) below the water table.