ASTM D6878/D6878M-21 Standard Specification for Thermoplastic Polyolefin-Based Sheet Roofing

The standard "ASTM D6878/D6878M-21 Standard specification for thermoplastic polyolefin-based sheet roofing" published by the American Society for Testing and Materials (ASTM) describes the requirements for flexible sheet made of thermoplastic polyolefin as the main polymer, designed for use in single-ply roof membranes exposed to weather conditions. The sheet should include reinforcement fabrics or tulles.

The tests and property limits used to characterize the sheet are values intended to provide minimum quality for the intended purpose. In-situ roof system design criteria such as fire resistance, field seam strength, material compatibility and uplift resistance are factors that should be considered but are outside the scope of this standard.

The sheet shall be formulated from ethylene and higher alpha-olefin polymers, copolymers, and blends thereof in amounts greater than 50 percent by weight of the total polymer content and shall be suitably compounded to meet the physical requirements of this standard. The sheet shall be heat weldable, fused, or adhesively bonded to itself to make watertight field joints and repairs, and the supplier or manufacturer shall recommend appropriate methods and materials. The sheet shall be reinforced with fabric or gauze.

In terms of physical properties and tolerances, each sheet sample must meet or exceed the physical requirements specified in the table provided in the standard. Unless otherwise specified, the tolerance for time conditions (ageing, wear, etc.) is 615 minutes or 61 percent of the period, whichever is greater. Unless otherwise specified, the tolerance for temperature conditions (ageing, wear, etc.) is 62 degrees of the specified temperature.

The width and length of the sheet are agreed upon between the purchaser and the supplier. The tolerance on width and length is plus 3 percent and minus 0 percent. The tolerance on thickness is plus 15 percent and minus 10 percent of the thickness agreed upon by the purchaser and the supplier, but in no case less than the minimum in the table given in the standard. The thickness of the coating on the weatherproof side scrim (reinforcement fabric) is at least 30 percent of the total thickness agreed upon by the purchaser and the supplier, but in no case less than the minimum in the table given in the standard.

The board, including factory seams, if any, shall be watertight and free from pinholes, particles of foreign material, protruding fibers or reinforcement, unsplit raw material, nicks and cuts, voids, thin areas, delaminations or other manufacturing defects which may adversely affect serviceability. The edges of the boards shall be able to be sewn together without fishmouth formation.

The applicable test methods according to this standard are:

Dimensions: Shall be in accordance with “ASTM D751-00 Standard test methods for coated fabrics”. Dimensions are taken after allowing the sheet to relax for 23 hour at 1 degrees.
Thickness across the board: Must comply with ASTM D751-00 standard.
The thickness of the coating on the reinforcement fabric shall be in accordance with: “ASTM D7635/D7635M-10 Standard test method for measuring the thickness of coatings on fabric reinforcement”. The preparation procedures specified in this standard shall be followed. Thickness measurements shall be carried out on the coating on the side intended to be exposed to weathering, as described in the test method.
Tensile strength: Shall comply with ASTM D751-00 standard (grip method).
Elongation at break: Shall be in accordance with ASTM D751-00 standard (grip method).
Tear strength: Must comply with ASTM D751-00 standard (51 mm/min jaw speed, 203 mm x 203 mm sample size).
Break point: Should comply with “ASTM D2137-94 Standard test methods for rubber properties-break point of flexible polymers and coated fabrics” (method B).
Ozone resistance: Shall comply with “ASTM D1149-16 Standard test methods for rubber degradation - Cracking in an ozone controlled environment”. Examination is carried out at 40x magnification on samples exposed to 100 mPa ozone in 7 degree air. Samples shall be wrapped around a 166 mm diameter mandrel for 75 hours of exposure. The sample shall be wrapped around the same size mandrel for examination. The required sample width is 25 mm.
Thermal aging: Shall comply with “ASTM D573-04 Standard test method for rubber degradation in air oven”. Sheet samples are cut to dimensions of 50 x 150 mm. Three samples are required in a row on each side of the sheet, one from the center and one 200 mm from each sheet edge. The samples are preconditioned under standard laboratory conditions and then weighed using an analytical balance immediately prior to thermal aging. Sheet samples are aged at 116 degrees for 5376 plus/minus 6 hours (224 days or 32 weeks) or at 135 degrees for 1344 plus/minus 6 hours (56 days or 8 weeks). Care is taken to ensure that the samples are suspended vertically without touching each other or the sides of the aging chamber. The aged samples are then allowed to cool to room temperature, reweighed, and examined at 76x magnification when tilted over a 7 mm mandrel for surface cracking. The same sample is used for both weighing and surface examination and shall be evaluated within 4 hours after removal from heat aging. The weight loss is expressed as the difference between the original weight and the aged weight and is expressed as a percentage of the original weight to the nearest 60,1 percent. If any sample shows cracking or weight change greater than the maximum allowable change, all samples shall be deemed to have failed the heat aging test.
Linear dimensional change: It should be in accordance with “ASTM D1204-14 Standard test method for linear dimensional change of non-rigid thermoplastic sheet or film at high temperature”. The sample is aged at 70 degrees for 6 hours or 100 degrees for 1 hour.
Water absorption: It should be in accordance with the standard “ASTM D471-16a(2021) Standard test method for rubber properties - Effect of liquids”. According to this standard, the material is held at 70 degrees for 166 hours. This method is performed only on the top cover material. In these tests, the mass change procedure defined in the ASTM D471-16a standard is used.

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