| June 1, 2018

Know the rules for applying I.R. structural adhesives

Repairing bonds using impact resistant I.R. structural adhesives can present some steep challenges. “The glue doesn’t tell you what it is or how to fix it,” says GM Lead Service Engineer Bob Hiser. That’s where proper training and OEM repair instructions come into play. Along with these tools, Hiser provides the following four rules to ensure I.R. structural adhesives are repaired properly all of the time.

RULE #1: Use I.R. structural adhesives wherever any adhesive needs replaced.

Practically every shop is going to have an assortment of adhesives to cover a variety of repairs. Hiser says when it comes to GM vehicles, always stick to I.R. structural adhesives, with one exception—replacing the adhesive used on door skins. Everywhere else, I.R. structural adhesives should be applied. This may seem counterintuitive for repairers used to working with multiple glues, but there’s good reason to stay with these super-strong adhesives. One, this strategy helps shops avoid mistakenly using a non-structure adhesive where one is needed—which can significantly impact how a vehicle handles. Also, I.R. structural adhesives provide the strongest possible bond, so why not use them everywhere?

RULE #2: Always include a mechanical bond.

As tough as impact resistant I.R. structural adhesives are, they can’t do their job alone. They must always accompany a mechanical bond of some type — a resistance weld, rivet, screw, etc. There are no exceptions to this rule.

RULE #3: Avoid MIG Plugs.

There is, however, one exception when it comes to the types of mechanical connections that can be used with I.R. structural adhesives. MIG plugs must NEVER be employed since they can damage the adhesive bond. Hiser notes that properly cured I.R. structural adhesives work exceptionally well with resistance spot welding. In areas where a spot weld cannot be applied, shops instead should turn to structural rivets or flowform screws.

RULE #4: Use only recommended I.R. structural adhesives.

It wasn’t that long ago when shops were fairly restricted when it came to selecting approved I.R. structural adhesives. Today, four I.R. structural adhesives may be used on GM products:
• Lord Fusor 2098 • Ashland 5770P • 3M 7333 • SEM 39757

As always, each of these adhesives must be applied using its own set of instructions. Fortunately, the steps are similar, and these adhesives are all easily dispensed, making application even easier.

One final point to keep in mind when working with I.R. structural adhesives is their significant contribution to ride quality. These adhesives substantially reduce road noise and play a key role in how a vehicle feels to drivers and occupants. When repaired properly, they return a vehicle to true pre-accident condition. Anything less and the vehicle owner probably will know right away a shop hasn’t done its job. Avoid these troubles by sticking to the rules.

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Category: The Technical Side