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November 9, 2017 - Window & Door

Rack Testing: What it is, and How it Helps Determine Construction Sealants for a Project

In all markets, it’s important to conduct adhesive trials and tests prior to selecting a product. For the construction market in particular, contractors opt for additional testing to ensure a product can withstand environmental elements and maintain building integrity.

Bostik recommends jobsite adhesion testing. However, contractors often also conduct “rack testing” on their own accord.

What is Rack Testing?

Rack testing is a process that tests a construction sealant on specific performance aspects including:

  • Weathering while under compression
  • Extension of cured sealant

By understanding how a sealant or adhesive responds to the elements (wind, rain, dirt, etc.), a contractor gains a better understanding of how the product can compensate for cyclic (expansion and contraction) movement over time. This is important, because a sealant’s main purpose is to seal the elements out of structure during any joint width. A joint width moves due to thermal changes, and a chosen sealant must be able to adjust accordingly without breaking its seal.

800x480_133. Product Safety Considerations

How Does Rack Testing Work?

A contractor chooses various product test specimens to try. A third party lab assembles the specimens (also called coupons) into a particular movement (either expanded or contracted). They are then are forwarded to the contractor and placed on the rack.

This rack can include specific types of substrates to adhere the product to or can use elements representative of actual substrates. For example, the industry typically looks at mortar as representative of a porous substrate and aluminum or glass as a non-porous substrate.

When the contractor receives the specimens, they are either expanded or contracted prior to testing. This serves to replicate when the given product would be installed. For instance, joints are wider in the winter when building materials contract. Joints are compressed in the summer and appear more narrow.

sealant failures

Six months later, the coupons are sent back to the labs and adjusted. If they had initially been expanded, they are then re-assembled to be contracted and demonstrate compression.

The intent with doing so is to have the joints (sealants) experience movement over an extended period of time, i.e. six month exposure to the colder months and then an additional six months exposure to the warmer months.

What Do the Results Show?

Upon completion of the rack testing process, contractors are able to successfully see how various products perform in environmental conditions. At this point, they are able to more confidently make their selection and understand the product’s performance before application.

For more information on this process and the importance of testing, call 800-7-BOSTIK.

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