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30 January 2013

Faith-based specifications

One of the most difficult things specifiers do is try to decide if one product is equivalent to another. Fortunately, many product characteristics are based on industry standards, which can make those products easier to specify and to evaluate.

For example, many hollow metal door manufacturers produce doors and frames that comply with either Steel Door Institute (SDI) or Hollow Metal Manufacturers Association (HMMA) standards. In fact, many manufacturers' products comply with both industry standards, and standards produced by the two organizations are similar. There are differences, but at least the standards are available and one can quickly tell if a hollow metal door complies with one or the other - assuming you have faith in the industry standards.

Other products can be far more difficult to evaluate…
These products use reference standards to some extent, but specify properties in different ways. Let's compare the manufacturers' specifications for three similar floor coatings (the manufacturers' representatives for these coatings consider them to be similar and competitive).
  • Compressive strength ranges from 10,000 to 15,000 PSI. One manufacturer says that is achieved after seven days, the others don't indicate how long it takes.
  • Tensile strength by one ASTM ranges from 1,640 to 1,750 PSI. Two of the manufacturers give a second tensile strength by a different ASTM, at 4,000 and 6,000 PSI.
  • Flexural strength varies from 3,700 to 4,300 PSI.
  • One manufacturer states impact resistance as depth of indentation, another states it in foot-pounds by the same reference standard, the third states it as in./lb, using a different ASTM.
  • For abrasion resistance, using the same ASTM, one claims 0.04 gr, another claims 0.1 gm, and the third claims 70-90 mg.
  • Two indicate flammability as self-extinguishing by one ASTM. By another ASTM, one indicates less than 1.07 watt/sq. cm, and one of the others says its product is Class I.
  • Water absorption is listed by one as 0.2%, by another as 0.3% by a different ASTM.
  • Surface hardness ranges from 65 to 95.
  • Only one addresses linear expansion.
  • One gives VOC content in grams per liter, one by compliance with EPA standards, and one says nothing about it.
  • Adhesion to concrete is expressed as concrete failure for two of the products.
  • Application rates are given for two of the products; they are similar but not identical.
  • The values are sometimes expressed differently for the same product in different sources.  
Given these inconsistent properties, how can one be sure these three products are equivalent? How can properties be compared when different reference standards are used? What should a specification say to allow these three products? Should specified properties be the lowest given by the manufacturers? What about those properties that are ignored by one or more of the manufacturers?

The problem is exacerbated by a lack of rational standards - standards that are based on analysis and meaningful properties. Most standards are based on what is available; rarely do I see an analysis done to determine what a property or a material thickness should be. Hollow metal door faces are 16 gauge not because a test indicates metal of that thickness performs in a certain way, but because that's the way they are made.

In the coating example, the lowest compressive strength is 10,000 PSI. Is that necessary? Would a coating with a compressive strength of 8,000 PSI, or even 5,000 PSI, work as well? Is the specified abrasion resistance a good value, or should it be higher? If the specification requires 10,000 PSI and a proposed product reaches only 9,999, is that good enough? Without a rational standard - one that states that a certain PSI is needed - we can only guess.

Standards also exist for many installation procedures. The Tile Council of North America explains how ceramic tile is to be installed, and the Gypsum Association publishes GA216 - Application and Finishing of Gypsum Panel Products, which explains how gypsum board partitions are to be installed. These standards make it relatively easy to know if an installation complies with the standards - assuming you have faith in the manufacturers' published data.

Most installation standards probably are based on experience; I'm sure the coating manufacturers tested various application rates before writing their installation instructions. But what about industry standards? Must drywall screws be installed at six inches on center, or will seven inches work as well? And how often do we verify what we get? I suspect very few firms test installed coatings to verify compliance with anything other than thickness; most have faith in the installers.

Given the vagaries of manufacturers' product information, how can you evaluate a prior approval request or a request for substitution? If the products in the specification vary as much as those in the coatings example, how do you know if another product with different properties will or won't work?

We often ask for coating samples, and get the typical stick showing each layer of the assembly. But what does that tell us? Don't they all look pretty much the same? Can you tell what's on the stick? When you visit a building where the coating is installed, do you know what's there? Can you see the layers? And, by the way, when a manufacturer's representative offers to show you examples of installed products, you can bet you won't see an installation that didn't work. Visiting existing installations can be useful - assuming you have faith in the person showing it to you.

Despite these problems, we do our best to specify characteristics that are meaningful, and to specify products that are similar enough to be considered equivalent. In the end, we often have little choice but to trust our product representatives, especially our Go-To Guys.

We need facts, but we also must have faith.

© 2013, Sheldon Wolfe, RA, FCSI, CCS, CCCA, CSC


  1. This is very interesting since we are considering a total home renovation. We also want to get ceramic tiles in the bathroom and kitchen. I have several questions to ask the contractor now.

    1. Maureen: In some ways, residential work is easier that commercial work, simply because of the scale. However, it often happens that a contractor will use the most familiar product, even if the drawings or specifications require something else. A few years ago, an attorney I know had a custom home built, with a fairly complete set of specifications, which is unusual for residential construction. Even though the specifications required solid core doors, the contractor installed hollow core doors.

      It's a good idea to discuss each product in detail, identifying each product by name and model number; use manufacturer's literature if available.

  2. Thanks for identifying one of the many elephants in the room when it comes to specs. Very few architects seem to have these questions, or are willing to verbalize them. They are too detailed; too much to keep track of, especially if you have the alternative of focusing on design details! But that doesn't mean they shouldn't be asked, that the specification process shouldn't be logical and make sense, just like anything else...

  3. Thanks for sharing this post!
    That was incredibly informative

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