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Understanding ASTM Leads to Informed Roof Choices

 

Anyone who has ever read an ASTM publication will quickly observe that these documents fall into two distinct categories:  a specification and a test method. Unscrupulous manufacturers make a game out of padding their data sheets with tests that are irrelevant to the roofing system described. Understanding the significance of specs and methods will prevent architects, building owners, and facility managers from making uninformed roofing choices.  

ASTM – Specifications vs. Test Methods

Specifications

ASTM Specifications tell the reader the suggested values (i.e., strength, elasticity, softening point, tear resistance, mode of failure etc) for a component or system.  Specifications are developed in ASTM committees made up of experts in their fields — ranging from adhesives to zippers — and serve as the guidelines for the specific building component. 

In the case of roofing, ASTM has a multitude of specifications for every facet of the roof — from what kinds of asphalt to use in certain conditions, to the expected strength, elasticity, tear strength of a modified bitumen membrane, to the type and quantity of mineral surfacing one should have on a modified asphaltic membrane. 

The ASTM specifications for roofing act as the benchmarks for the components that make up a roof and the values within the specifications should be considered the most important when choosing a roof membrane.  The following list shows the primary specifications (or guidelines) used by typical industrial roof manufacturers.  By way of example, ASTM D1668 contains the important features that all glass fabrics need in order to be considered a sufficient glass fabric used in roofing and waterproofing.

Typical Specifications That Govern the Composition of Modified Membrane Systems

ASTM #

Description

D1668

Standard Specification for Glass Fabrics (Woven or Treated) for Roofing and Waterproofing

D1863

Standard Specification for Mineral Aggregate Used on Built-Up Roofs

D2178

Standard Specification for Asphalt Glass Felt Used in Roofing and Waterproofing

D2626

Standard Specification for Asphalt-Saturated and Coated Organic Felt Base Sheet Used in Roofing

D312

Standard Specification for Asphalt Used in Roofing

D450

Standard Specification for Coal-Tar Pitch Used in Roofing, Dampproofing and Waterproofing

D4601

Standard Specification for Asphalt-Coated Glass Fiber Base Sheet Used in Roofing

D4990

Standard Specification for Coal Tar Glass Felt Used in Roofing and Waterproofing

D6162

Standard Specification for SBS Modified Bituminous Sheet Materials Using a Combination of Polyester Glass Fiber Reinforcements

D6163

Standard Specification for SBS Modified Bituminous Sheet Materials Using Glass Fiber Reinforcement

D6164

Standard Specification for SBS Modified Bituminous Sheet Materials using Polyester Reinforcements

What is important to point out here is that the specifications do not describe how to do the tests to arrive at the value, but simply state the recommended values for the specific technology.  It is the test method’s job is to tell the reader how to arrive at the numbers in the specification.

Methods (or Standard Practice)

Methods describe the process necessary to obtain the values in a given specification.  Usually, the ASTM specification lists the types of ASTM methods that can be used to arrive at the recommended value.  It is important to note that the method will not tell the reader the values that are expected in a specification, but it sometimes asks for the tester to be within a certain error spread or deviation.

For example, ASTM D5147 describes the method for sampling and testing modified bituminous sheet material and is the instruction manual for roof manufacturers to test asphaltic membranes.  It describes how to cut, arrange, prepare the testing equipment, condition the samples, the ideal ambient testing temperature and humidity at the time of the test, as well as a host of other details. 

However, D5147 does not tell the tester what the average strength of a glass felt product should be.  For the proper value, you must refer to the ASTM D2178 specification. There are some cases where a specification is not available; in these cases, only test methods are listed.

When comparing the myriad of values in supplier's data sheets citing all kinds of ASTM references, the inexperienced reader can easily get lost in deciding which values are important and which aren't.  When in doubt, you can visit the ASTM website, type in the ASTM number referenced and check to see if the words "Specification" or "Test Method" (aka, "Standard Practice") are in the title line.  If it's the former, you know the product meets the specifications set forth by the panel of experts responsible for that particular product.  If it's the latter, you'll know the product was tested properly, but will also be aware that the value may not be necessarily part of the specification, that it could just be extra information to help bolster the data sheet.

Conclusion

To summarize, ASTM specifications tell the reader what values are expected when testing a roof component using a suitable ASTM test method.  When looking over a technical data sheet, ask yourself these questions: 

  • Was the testing described in accordance with the ASTM specification or is this just a testing method? 
  • Does the actual specification call for the particular test method used or was the test method just added to provide another data point, without actual relevance to the spec requirements? 

A well-informed manufacturer’s representative should be able to explain how the data provided is relevant.  

 

 

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