Permeability testing of bituminous waterproofing materials is a fundamental quality control procedure that verifies whether bitumen membranes, coatings, and sheets can resist water penetration under hydrostatic pressure and limit water vapor transmission. This technical article explains the applicable standards such as GB/T 328.10, EN 1928, EN 1932, and ASTM D5385, typical sample types, test conditions, and acceptance criteria used by accredited third-party laboratories and manufacturers worldwide.
Technical Overview
Bituminous waterproofing materials—including Styrene-Butadiene-Styrene (SBS) modified bitumen membranes, Atactic Polypropylene (APP) modified bitumen membranes, self-adhesive bituminous sheets, and bituminous coatings—are among the most widely used barriers against water ingress in building envelopes, roofs, basements, tunnels, and bridge decks. Permeability testing evaluates the ability of these materials to prevent the passage of liquid water under pressure and, where relevant, to control the diffusion of water vapor through the membrane layer.
The core performance property for most product standards is impermeability, sometimes described as watertightness or water-tightness under hydrostatic pressure. A specimen that allows any visible seepage, wetting, or droplet formation on its underside during the test is considered to have failed. Additional related properties include water absorption and water vapor permeability, which characterize the long-term moisture behavior of the material. Testing is typically performed by manufacturers for factory production control and by accredited third-party laboratories for type testing, product certification, and compliance verification against standards published by ISO, EN, ASTM, and GB standardization organizations.
Testing Samples
SBS Modified Bituminous Waterproofing Membranes
Elastomeric membranes modified with SBS polymers, produced in accordance with GB 18242 or equivalent international product standards, are the most common samples submitted for permeability testing. These products typically feature polyester or fiberglass reinforcement and surface finishes such as polyethylene film, fine sand, or mineral granules, and the required test pressure depends on the surface type.
APP Modified Bituminous Waterproofing Membranes
Plastomeric membranes modified with APP or APAO polymers, covered by GB 18243 and related specifications, are used in high-temperature and exposed roofing applications. They are tested for impermeability using the same hydrostatic pressure principle applied to their designated weather-facing surface.
Self-Adhesive Bituminous Membranes
Self-adhesive polymer-modified bituminous sheets, including those conforming to GB 23441, are tested in their delivered condition. Because their performance depends on the integrity of the adhesive layer and release film, specimen preparation and conditioning are strictly controlled before testing.
Bituminous Waterproofing Coatings
Waterborne or solvent-based bituminous and polymer-modified bituminous coatings, including products referenced in JC/T 408 and comparable standards, are cast onto suitable substrates or release panels, cured under specified conditions, and then tested as free films or as bonded systems for hydrostatic pressure resistance.
Other Bituminous Products
Asphalt shingles, saturated felts, primers, damp-proofing courses, and specialty membranes for bridge decks and tunnels can also be evaluated. For all sample types, specimens are normally conditioned at a standard atmosphere of (23 ± 2) °C and (50 ± 5) % relative humidity prior to testing.
Testing Items
The scope of permeability-related testing for bituminous waterproofing materials typically includes the following items, each mapped to a recognized test method:
- Impermeability under static hydrostatic pressure (pass/fail at a specified pressure and duration, for example 0.3 MPa maintained for 30 min, or 0.2 MPa maintained for 120 min for polyethylene-film-faced products).
- Watertightness of flexible sheets for roof waterproofing in accordance with EN 1928.
- Hydrostatic pressure resistance to failure in accordance with ASTM D5385, reporting the pressure at which the first leak occurs.
- Water vapor transmission rate (WVTR) and permeance in accordance with EN 1932 or ASTM E96.
- Water absorption, expressed as the percentage of mass change after a defined immersion period, in accordance with GB/T 328.26.
- Optional supporting properties that correlate with permeability performance, such as tensile strength retention after water immersion and joint seam watertightness.
Testing Methods
Static Hydrostatic Impermeability Test (GB/T 328.10-2007)
This is the primary impermeability method for bituminous sheets in the GB/T 328 series. Square specimens, commonly 150 mm × 150 mm, are clamped in an impermeability apparatus so that water pressure acts on the upper, weather-facing surface of the membrane through a porous plate. The pressure is raised to the value specified in the product standard and held for the specified duration, typically 0.2 MPa for 120 min or 0.3 MPa for 30 min. Immediately after the test, the underside of each specimen is examined; the requirement is met when no seepage of water is observed on any of the tested surfaces.
Watertightness of Flexible Sheets (EN 1928)
The EN 1928 procedure applies water under defined pressure to one face of a clamped sheet specimen for a set period. After exposure, the reverse side is inspected for signs of water penetration. This method is applicable to bitumen, plastic, and rubber sheets used for roof waterproofing and forms part of the harmonized European product standards for these materials.
Hydrostatic Pressure Resistance (ASTM D5385)
ASTM D5385 determines the resistance of waterproofing membranes to hydrostatic pressure, particularly fluid-applied and sheet systems intended for below-grade use. The membrane is applied over a specified substrate or support, and water pressure is increased in controlled increments until leakage is detected. The method reports the maximum pressure sustained without leakage, providing a quantitative failure threshold rather than a simple pass/fail result.
Water Vapor Permeability (EN 1932 and ASTM E96)
These methods measure the rate of water vapor diffusion through bituminous sheets using cup-type assemblies. In the wet-cup configuration, the cup contains water and vapor migrates outward through the specimen; in the dry-cup configuration, a desiccant draws vapor inward. Weight changes over time are used to calculate the water vapor transmission rate, commonly expressed in g/(m²·24 h), and the water vapor permeance. Low permeance values are essential for vapor control layers and cold-roof designs.
Water Absorption (GB/T 328.26)
Conditioned specimens are dried to constant mass, fully immersed in water at a controlled temperature for the specified period, surface-dried in a defined manner, and reweighed. The increase in mass, expressed as a percentage, indicates the water absorbed by the material. Excessive absorption can signal porosity, reinforcement exposure, or binder deficiency, all of which may compromise long-term impermeability.
Applications
Permeability test results directly support specification, certification, and construction acceptance decisions across a wide range of engineering scenarios:
- Exposed and protected roofing systems, where membranes must withstand wind-driven rain and standing water.
- Basements, foundations, and podium slabs subject to sustained groundwater head pressure.
- Tunnel and subway linings, where composite bituminous membranes must remain watertight under continuous seepage pressure.
- Bridge deck waterproofing, where impermeability testing complements adhesion and fatigue requirements.
- Water conservancy structures such as reservoirs, canals, and irrigation channels.
- Environmental containment works, including landfill caps and secondary containment barriers.
- Product development and incoming material inspection, enabling manufacturers to compare binder formulations, reinforcement types, and surface treatments.
FAQ
What are the typical pass criteria for the impermeability test?
For most modified bituminous membranes under GB product standards, the requirement is no water seepage on the undersurface after holding 0.3 MPa for 30 min, or 0.2 MPa for 120 min for products finished with polyethylene film. The exact pressure and duration must always be taken from the applicable product standard or project specification.
How are membranes with mineral granule or sand surfaces tested?
The specimen is oriented so that water pressure is applied against the granule or sand surface, reproducing service exposure. The porous plate of the apparatus ensures uniform pressure distribution across the textured face.
Can bituminous coatings be tested for hydrostatic pressure resistance?
Yes. Coatings are first applied and cured on a specified substrate or as free films at the manufacturer's recommended thickness, then evaluated using methods such as ASTM D5385, which reports the pressure at first leakage.
Why is water vapor permeability tested if the membrane is already watertight?
Liquid water resistance and vapor diffusion are distinct properties. In insulated roofs and walls, excessive vapor transmission can cause interstitial condensation, so designers use measured permeance values from EN 1932 or ASTM E96 to select appropriate vapor barriers and calculate condensation risk.
How should samples be submitted for third-party testing?
Samples should be taken from representative production lots, at least one full roll or the equivalent minimum length specified by the laboratory, accompanied by product data such as thickness, reinforcement, surface finish, and the target standard. Specimens are then cut and conditioned at standard temperature and humidity before testing begins.