Water absorption testing is a fundamental quality control procedure for roll materials such as bituminous and polymer waterproofing membranes, quantifying how much moisture a product takes up when immersed under controlled laboratory conditions. This article explains the standard specifications, sample requirements, test items, methods, and reporting requirements that accredited third-party laboratories follow when evaluating the water absorption of roll products. By understanding these specifications, manufacturers, contractors, and project owners can verify compliance with applicable standards and protect the long-term performance of waterproofing systems.
Technical Overview
Water absorption refers to the increase in mass of a roll material after it has been fully immersed in water for a specified period under controlled temperature conditions. For waterproofing membrane rolls, the result is typically expressed as the percentage of mass gained relative to the original dry mass. Low water absorption indicates a dense, impermeable structure, while excessive absorption can lead to swelling, loss of tensile strength, blistering under thermal exposure, reduced adhesive bonding, and premature failure of the waterproofing system.
The test principle is straightforward: conditioned specimens are weighed, immersed in distilled water at a controlled temperature for a defined duration, removed and quickly dried of surface water, and then reweighed. The mass difference determines the absorption rate. Extended immersion schedules are used to approach saturation, and supplementary weighings after re-drying can quantify the loss of water-soluble constituents, which is important for materials that may leach plasticizers or additives.
Testing programs are governed by recognized national and international standards, including ISO 62 and its Chinese counterpart GB/T 1034 for plastic sheets, ASTM D570 for plastics, the GB/T 328 series for building sheets for waterproofing, and GB/T 1690, ASTM D471, or ISO 1817 for vulcanized rubber sheets. Product standards such as GB 18242, GB 18243, GB 12952, and GB 18173.1 define the applicable method, immersion schedule, and acceptance limits for specific roll types.
Testing Samples
Samples must be representative of the production lot. They are normally taken from positions at least one meter from the roll ends, cut across the full width, and clearly labeled to identify batch, production date, and surface finish. All specimens are conditioned before testing to ensure repeatable results.
Bituminous Waterproofing Membrane Rolls
This category includes SBS and APP modified bitumen membranes and petroleum bitumen base sheets, finished with polyethylene film, fine sand, or mineral granules. Separator sheets are removed before specimens are cut, and the membrane is tested in its delivered state, including its surface finish, because the finish strongly influences water uptake at the surface.
Polymer Waterproofing Membrane Rolls
This category covers homogeneous and reinforced sheets made of PVC, TPO, EPDM, HDPE, EVA, and similar polymers. These materials are generally tested according to the immersion procedures of ISO 62, GB/T 1034, or ASTM D570, with specimen geometry adapted to the thickness of the sheet.
Rubber and Composite Rolls
Vulcanized rubber sheets, laminated composite rolls, and polymer-based water-stops are evaluated using liquid-resistance methods such as GB/T 1690, ASTM D471, or ISO 1817, which measure both mass change and volume change after immersion. For intentionally water-swelling products, uptake behavior is assessed against the swelling requirements of the corresponding product standard.
Other Roll Materials
Foamed sheet rolls, floor covering rolls, insulation rolls, and packaging rolls can also be assessed with equivalent immersion methods when project specifications or purchase contracts require verification of moisture behavior.
Testing Items
Depending on the product standard and the purpose of the evaluation, a water absorption test program for roll materials may include the following items:
- Short-term water absorption rate after 24 hours of immersion
- Long-term immersion absorption after 7 days or 28 days, and saturation water content
- Corrected water absorption accounting for the loss of water-soluble matter
- Thickness swelling and dimensional change after immersion
- Visual evaluation of the surface after immersion, including blistering, delamination, and coating adhesion
- Water absorption under accelerated conditions, such as elevated temperature or boiling water immersion
- Compliance judgment against the acceptance limits of the applicable product standard
Testing Methods
Specimen Preparation and Conditioning
Specimens are cut with clean, sharp tools to avoid edge damage and deformation. Common specimen sizes are 100 mm × 100 mm pieces for waterproofing membranes, 60 mm × 60 mm pieces for plastic sheets per ISO 62, or 76.2 mm × 25.4 mm strips and discs per ASTM D570, depending on the governing method. A minimum of three specimens is generally required, distributed across the width of the roll. Before testing, specimens are conditioned at 23 ± 2 °C and 50 ± 5% relative humidity for at least 24 hours, or until consecutive weighings show mass stability. Each specimen is then weighed to the nearest 1 mg to obtain the initial mass.
Immersion Procedure
Specimens are fully immersed in distilled or deionized water maintained at 23 ± 1 °C, or at the temperature specified by the product standard. Specimens must be separated from each other and from the container walls, with water depth of at least 20 to 30 mm above the uppermost specimen. Standard immersion durations include 24 hours for routine quality control, and 7 days or 28 days for long-term and saturation assessment. At the end of the immersion period, each specimen is removed, surface water is removed with a dry, lint-free cloth, and the specimen is reweighed immediately, typically within 60 seconds of removal, to prevent evaporative loss. Where soluble-matter loss is relevant, the specimen is subsequently re-dried to constant mass and weighed a third time.
Calculation and Expression of Results
The standard water absorption result is calculated as the mass increase divided by the original conditioned mass, multiplied by 100, and reported as a percentage. When soluble-matter loss is determined, the corrected calculation incorporates the re-dried mass so that the reported value reflects true water uptake rather than a net change reduced by leaching. The report presents individual values, the arithmetic mean, and the deviation among specimens, together with any thickness or dimensional changes and surface observations.
Test Report
A complete report identifies the sample and its source, the test standard applied, specimen dimensions and quantity, conditioning parameters, water quality and temperature, immersion duration, all measured masses, calculated absorption values, visual observations, and a clear statement of conformity or non-conformity with the specified limits.
Applications
Water absorption testing of roll materials supports quality and compliance decisions across the entire supply chain of building waterproofing:
- Factory quality control during membrane production and verification of raw material and formulation changes
- Type testing and product certification against national and international product standards
- Incoming material inspection on construction sites before installation
- Roofing, basement, tunnel, bridge deck, and reservoir waterproofing projects where moisture resistance is critical
- Research and development for comparing polymer grades, modifiers, and surface finishes
- Failure analysis, condition assessment of aged membranes, and technical dispute resolution
FAQ
What standards govern water absorption testing of roll materials?
Plastic and polymer sheets are commonly tested to ISO 62, GB/T 1034, or ASTM D570; building waterproofing sheets follow the relevant parts of the GB/T 328 series together with product standards such as GB 18242, GB 18243, GB 12952, and GB 18173.1; and vulcanized rubber sheets are assessed to GB/T 1690, ASTM D471, or ISO 1817. The applicable standard is determined by the material type and the specification of the project or purchaser.
What is an acceptable water absorption value?
Acceptance limits depend on the material class and the product standard. Dense polymer membranes are typically expected to show very low uptake, often not exceeding 1% to 2% by mass after immersion, while bituminous and composite rolls are commonly limited to a few percent. Intentionally water-swelling products have their own requirements. The limit for a given product must always be verified against its specific standard.
How many specimens are required?
Most methods require a minimum of three specimens per sample, cut from different positions across the roll width so that the result represents the whole product rather than a single location.
How long does the test take?
The routine 24-hour immersion test, including conditioning, can usually be completed within two to three working days. Extended 7-day or 28-day schedules, and accelerated elevated-temperature or boiling-water procedures, require correspondingly longer laboratory time, and the report turnaround should be confirmed with the testing laboratory in advance.
Why do some specimens show little mass gain or even lose mass?
Some roll materials contain water-soluble constituents such as certain additives or fillers that leach into the water during immersion. If leaching is significant, the measured mass gain understates true absorption. Recognized standards address this by requiring re-drying and a corrected calculation based on the final dry mass.
Can the test be performed at elevated temperature?
Yes. Elevated-temperature immersion and boiling-water exposure are used as accelerated conditioning to screen materials or evaluate performance in severe service environments. Because results are temperature- and duration-dependent, the exact conditions must be clearly stated in the test report and compared only with results obtained under the same conditions.