Tear Strength Testing of Emulsion-Coated Glass Fiber Fabric: Standards, Methods, and Quality Control

Emulsion-coated glass fiber fabric is a key reinforcement material in waterproofing membranes, façade insulation systems, and industrial textiles, where tear resistance is a critical performance parameter. This article provides a comprehensive technical guide to tear strength testing of emulsion-coated glass fiber fabric, covering applicable international standards, specimen preparation, test procedures, and result interpretation. Understanding these methods enables manufacturers, testing laboratories, and specifiers to verify product quality and ensure reliable long-term performance.

Technical Overview

Emulsion-coated glass fiber fabric is a woven textile produced from continuous or staple glass fiber yarns and finished with a polymer emulsion, most commonly acrylic, styrene-acrylic, or polyvinyl acetate based. The emulsion coating binds individual glass filaments into coherent yarns, improves abrasion resistance and dimensional stability, reduces linting and fuzzing during handling, and enhances adhesion to bitumen, resins, and cementitious matrices. These fabrics are widely used as reinforcement scrims in bituminous waterproofing membranes, external thermal insulation composite systems (ETICS), filtration media, and thermal insulation facings.

Tear strength describes the ability of a fabric to resist the propagation of an initiated cut or slit under load. Unlike tensile strength, which measures resistance to a uniformly applied force across the full specimen width, tear testing measures the localized force required to continue tearing along a deliberate incision. Because coated fabrics in service frequently encounter cuts from fasteners, aggregate, or sharp edges, tear strength is one of the most important durability indicators for emulsion-coated glass fiber fabric.

The tear behavior of glass fiber fabric is strongly influenced by the coating. A moderate binder add-on increases yarn pull-out resistance and generally raises tear force, while excessive coating can rigidly lock the yarn intersection points, prevent the formation of the characteristic tear triangle, and reduce propagation resistance. Systematic tear testing therefore supports coating formulation optimization, manufacturing process control, and final product qualification. Commonly applied standards include:

• ISO 13937 series (Parts 1 to 4) covering pendulum, trouser, wing, and tongue methods for fabric tear properties
• ASTM D1424 for falling-pendulum (Elmendorf type) tear strength
• ASTM D2261 for tongue (single rip) tear strength using a constant-rate-of-extension (CRE) tensile tester
• ASTM D5733 for trouser tear strength using a CRE tensile tester
• ISO 4674 series for tear resistance of rubber- or plastics-coated fabrics
• GB/T 3917 series, the Chinese national standards harmonized with ISO 13937

Testing Samples

Trouser Specimens

The trouser (pants) specimen per ISO 13937-2 or ASTM D5733 is a rectangle of approximately 200 mm by 50 mm with a 100 mm cut made in the center of the long side, producing two legs that are clamped in separate grips. As the grips separate, the tear propagates along the cut line. This method is well suited to most coated fabrics and produces a complete force-displacement record from which the mean and maximum tear forces are determined.

Wing Specimens

The wing specimen per ISO 13937-3 features a shaped profile with a central slit; the two wings are gathered and clamped together while the opposite end is held in a second grip. The wing geometry reduces yarn slippage away from the tear path and is particularly useful for coated glass fabrics whose rigid yarns may migrate or produce off-axis tearing during trouser testing.

Tongue (Single Rip) Specimens

Tongue specimens per ASTM D2261 or ISO 13937-4 consist of a rectangular strip with a central cut that creates two tongues. One tongue is clamped in the upper grip and the body of the specimen in the lower grip, producing a single-rip tear through the fabric. ASTM D2261 typically specifies a 75 mm gauge length and a test speed of 254 mm/min.

Pendulum (Elmendorf) Specimens

Pendulum specimens per ISO 13937-1 or ASTM D1424 are small rectangular pieces, typically about 100 mm long and 63 to 75 mm wide depending on the standard and instrument, with a standardized initiating slit of approximately 20 mm. The specimen is torn by a falling pendulum, and the energy absorbed is converted directly into tear force. This method is fast and economical, making it popular for routine incoming inspection.

Sampling and Conditioning

Careful sampling and conditioning are essential for valid results. Recommended practice includes:

• Prepare at least five valid specimens for each direction (warp and weft); ten specimens improve statistical confidence
• Cut specimens away from selvedges and fabric ends, ensuring no two specimens share the same lengthwise yarns
• Clearly label each specimen with its test direction before cutting the initiating slit
• Condition specimens in the standard textile atmosphere per ISO 139 (20 ± 2 °C and 65 ± 4 % relative humidity) or ASTM D1776 for a minimum of 24 hours or until equilibrium is reached
• Cut slits precisely using sharp blades and templates; frayed, off-angle, or over-length slits invalidate results

Testing Items

Tear strength testing of emulsion-coated glass fiber fabric typically evaluates the following items:

• Warp-direction tear strength, tested with the tear propagating along the machine direction
• Weft-direction tear strength, tested with the tear propagating along the cross direction
• Maximum tear force in newtons (N) recorded during propagation
• Mean or average tear force derived from the tear plateau region of the force-displacement curve
• Five-peak mean or median values where the applicable standard requires peak-based evaluation
• Coefficient of variation and range, which reflect fabric uniformity and coating consistency
• Tear propagation mode, including clean yarn-by-yarn breakage, yarn pull-out, or coating delamination

A complete test report should state the standard and method used, test direction, number of specimens, individual and mean values, coefficient of variation, conditioning atmosphere, machine type, and the coating add-on or binder content of the sample where known.

Testing Methods

Constant-Rate-of-Extension (CRE) Method

In the CRE method, trouser, wing, or tongue specimens are tested on a calibrated universal tensile testing machine. For the trouser method per ISO 13937-2, a gauge length of 100 mm and a test speed of 100 mm/min are typical; each leg of the specimen is mounted in a separate grip with the slit aligned on the load axis. The test continues until the tear propagates through the required tearing distance while the force-displacement curve is recorded continuously. Specimens that slip in the grips, tear outside the designated zone, or fail by tensile break rather than tearing must be rejected and replaced.

Falling-Pendulum (Elmendorf) Method

In the pendulum method, the specimen is clamped between fixed and moving clamps, the pendulum is raised to its release position, and the slit is completed with the built-in cutter immediately before release. Upon release, the pendulum tears the specimen, and the pointer or digital display indicates the tear force. The pendulum capacity should be selected so that the reading falls within the calibrated working range of the instrument. Multiple specimens are tested in each direction and the results averaged.

Data Evaluation and Expression

For CRE methods, the tear region of the force-displacement curve is analyzed to determine the maximum force and, where required, the mean tearing force computed over the valid propagation length; some standards apply a five-peak or zone-based evaluation. Pendulum instruments provide a direct tear force reading corrected by the pendulum factor. For each direction, the individual values, mean value, and coefficient of variation are calculated and compared against the product specification. Results obtained by different methods are not interchangeable and must always be identified by method.

Factors Influencing Test Results

• Emulsion type, coating add-on (binder content), and degree of curing
• Glass yarn linear density, twist, weave construction, and fabric areal density
• Compatibility of the silane sizing or finish on the glass fibers with the coating emulsion
• Specimen cutting quality, slit geometry, and alignment within the grips
• Grip pressure, jaw face condition, and any yarn slippage during testing
• Conditioning state of the specimen, since coating stiffness varies with temperature and humidity

Applications

Tear strength data for emulsion-coated glass fiber fabric directly supports product qualification, incoming quality control, and failure analysis across a wide range of end uses, including:

• Reinforcement scrims for SBS and APP modified bituminous roofing and waterproofing membranes
• Reinforcement meshes for external thermal insulation composite systems and façade renders
• Gypsum board joint tape and drywall reinforcement fabrics
• Facings and jacketing for thermal insulation products
• Industrial filtration media and high-temperature protective textiles
• Backings for adhesive tapes, abrasive products, and molded composite surfacing layers

Verified tear performance helps manufacturers publish reliable technical data sheets, meet declaration-of-performance requirements, and provide fabricators with the confidence that the material will tolerate cutting, fastening, and site handling without tear propagation.

FAQ

Which tear test method is most appropriate for emulsion-coated glass fiber fabric?

The wing and trouser methods (ISO 13937-3 and ISO 13937-2) are generally preferred for coated woven glass fabrics because they run on a CRE machine and provide a full force-displacement record. The Elmendorf pendulum method (ISO 13937-1 or ASTM D1424) is widely used for rapid routine quality control. Because results from different methods are not directly comparable, the specific method should be agreed between supplier and purchaser in the product specification.

How many specimens should be tested?

At least five valid specimens should be tested in each direction (warp and weft). Additional specimens are recommended when variability is high or when statistical confidence is required. Specimens that slip in the grips, tear outside the designated tearing zone, or fail by tensile break should be discarded and replaced.

Why can tear strength decrease as coating add-on increases?

Light to moderate emulsion add-on improves filament cohesion and yarn pull-out resistance, which tends to raise tear force. Excessive binder, however, rigidly anchors the yarn intersections, prevents yarns from grouping into a tear triangle, and forces a more brittle line-by-line failure mode that lowers propagation resistance. Optimizing the add-on balances handling, coating adhesion, and tear performance.

What is the typical tear strength of emulsion-coated glass fiber fabric?

Values depend strongly on areal density, yarn count, weave, and coating level. Lightweight scrims below about 60 g/m2 may show tear forces of only tens of newtons, while heavy reinforcement fabrics can reach several hundred newtons. Acceptance criteria should therefore always be defined by the individual product specification rather than by a universal value.

Do warp and weft tear results differ?

Yes. Differences in yarn crimp, weaving tension, and coating penetration typically produce different tear behavior in the two directions, so warp and weft results must be measured and reported separately.

How should test results be reported?

Reports should include the standard and method used, test direction, number of specimens, individual values, mean value, coefficient of variation, conditioning atmosphere, machine and grip details, and any observed deviations such as slippage or off-axis tearing, together with the coating add-on of the sample where available.