Article The Truth About Static Load Limit Testing

Static load testing measures how a floor recovers after supporting an unmoved weight for a period of time. Most resilient flooring specifications reference ASTM Test Method F970, which specifies how to determine the indentation recovery properties of resilient flooring products when handling static loads. Learn more about testing methods — and the increase of modified test methods — to fully understand which numbers you should be looking at when considering commercial flooring needs.

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Bio-Flooring
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What is the Standard for Static Load Limit Testing?

To maintain quality standards that are uniform across the industry, manufacturers must design and construct flooring that tests and passes ASTM Test Method F970: Standard Test Method for Static Load Limit. The purpose of this test is to determine how a floor recovers, or how much of an indent remains, after the specified load has been applied to an uninstalled floor for a specific period of time.

Here’s how it works:

  • This method calls for a standard testing load in pounds per square inch (PSI), depending on the type of flooring
  • It’s important to note that the method does not cite a static load requirement higher than 250 PSI for any product specification covering the category of resilient flooring. For example:
    • Rigid Core: 250 PSI
    • Polyester Composition Tile (BBT): 250 PSI
    • Sheet Flooring: 250 PSI
  • This load is applied for 24 hours on an uninstalled piece of product; once time is up, the load is removed and the floor rests for 24 hours
  • The measured and reported value — the depth of the depression after 24 hours of rest — must be less than 5 mils to pass ASTM F970

This is the standard test method used by the flooring industry to determine the performance of the floor from a quality control standpoint. When making a final decision related to the durability of a product, static load limit is only one of a series of criteria that should be considered; other criteria include resistance to scratches, stains and gouging.

This is an example of a 5 mil depression, the maximum allowed to pass ASTM F970. Indentations at a 5 mil depression, even though they meet ASTM F970, could be very apparent and objectionable to an end user.

Does a Higher Static Load Limit Rating Mean Better Protection?

While ASTM F970 is the standard for the industry, it’s common to see modified tests where a much higher load was used. This type of testing is outside the scope of the test method, and published results often carry an asterisk to note the deviation.

Does this high PSI rating mean the floor will hold up better to heavy static loads? Not necessarily, but there’s a lot to consider. Before you spec the product, make sure you have realistic expectations about recovery from indent.

In accordance with ASTM methods, static load testing is currently performed on an uninstalled product, and the same test conditions used on an installed product may give very different results. Additionally, testing does not take into account any contribution to indentation that could result from adhesives, patches, or underlayments. Therefore, static load limit values are not a complete indicator of the product's installed performance.

Another factor to consider is that static load testing differs from dynamic load testing, which can be more applicable in segments like education, healthcare, and retail. Static load testing gently places load on the floor for a specific amount of time, gently removes the load at the end of the test, and then measures residual indentation after a period of resting time. Alternatively, dynamic loads are created where a load is placed on the floor, and then moved around the floor's surface by a rolling, sliding, or dragging motion. There are no industry-wide accepted methods to evaluate dynamic loads, a common occurrence in day-to-day commercial applications.

The decision on which flooring to choose, as it pertains to static load impact, shouldn’t just come down to which flooring is advertised as the highest PSI. Make sure you understand how the flooring was tested before you compare results. If both floors were not tested by ASTM F970, the results are likely not comparable.

For questions about static load limit testing and Armstrong Flooring testing methods, please contact Techline.