by Bob Beranek
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There was an interesting discussion recently that I thought I would bring up for readers to debate. The discussion is about the condition of the existing urethane bead once the glass is removed by the new wire-out tools. It seems that there is a belief that the bead is already trimmed to the proper height due to the design of the wire-out tools and that additional stripping is unnecessary. Also, there is some concern regarding the rough condition of the urethane bead when the new cord is used in the cut out. This brings to mind two questions.

Does the existing urethane bead need to be trimmed down or is the bead height adequate for bonding immediately?

What is the ideal surface for urethane bonding to itself, smooth or rough?

One of the selling points of the wire-out tool is that the existing urethane bead is cut closer to the pinchweld surface. This allows the technician to save time by not having to trim back the urethane bead for bonding. The directions given by adhesive manufacturers have been to trim back to 1-2 mm or 1/16” of the existing adhesive bead. The amount of bead left by the wire out tool depends on the design of the tool. The closer the wire is to the interior glass surface the closer the cut will be to the pinchweld. You will need to trim it back if there is more existing bead left by your particular tool. Remember that the 1-2 mm guideline is there for a reason and must be met as close as possible to the recommendation by the adhesive manufacturers.

There are basically two types of cut out material for the new wire-out tools, the wire or the cord. The wire cuts out the glass and leaves a smooth surface on the existing urethane bead. The cord usually leaves a rough surface. The smooth surface left by the wire is not a concern because we have been bonding to that type of smooth surface ever since we started to use urethane. The question that needs to be answered is what should be done with the rough surface left by the cord to promote adhesion?

Comments (6)

  1. […] TODAY’S BLOG: Part 2: Pinchweld Preparation […]

  2. daniel said on 13-02-2014

    A rough surface used as fundament for the new urethane might allow air bubbles remain trapped inside, no matter how fluid the new adhesive might be. Therefore, the bonding area is suspected to diminish.
    Personally, I would recommend the triming of the remained surface after the piano string cuttingin order to reach a plane, smooth basis for the new adhesive bead.

    • keith elder said on 13-02-2014

      pinchweld prep and glass prep is everything, if your urethane lets loose of either your going to have problems.

  3. keith elder said on 13-02-2014

    in my 31 years of autoglass managment/installation experience this is another example of “6 of 1, half dozen of the other”. there isnt a proper trim height im my opinion. there IS a proper windshield height for proper fit and finish for moldings, appearance ect. doesnt matter what urethane is left on the body. havent you guys done some jobs with butyl used?,, havent you done some jobs that the old urethane peeled off?,, so on and so forth so the main point i have is the main thing about the pinchweld is proper preparation for the new urethane to adhere to the body and glass and stop this worrying about how thick the urethane should be and by what cutout tool should be used. use what works for you, do a good job so you dont have to worry about that mom and her baby flying out of the windshield if they wreck the car. safety first..

    • daniel said on 18-02-2014

      Absolutely right !
      I strongly recommend technicians to grab an lift the trimmed snake ofcold urethane and keep it up and forward as the cutting blade or chisel continue the trimmering. This method forces the old snake to reveal any previous adhesion failure.
      I often reveal hidden rust spots on older vehicles, and just the plain cut without lift may not show those failures.

      • Keith Elder said on 21-02-2014

        yep and good points,, thats why i dont concern myself with 1 to 2 mm of adhesive left on the body because i DONT know what is underneath the old adhesive.. new car and old car both may have loose adhesive after glass is removed,, when you strain and stress the old adhesive it may cause a failure to adhere and you MUST know what is underneath it in order to be sure of a good proper pinch weld preparation… rust, seamsealer, holes in pinchweld ect. must be exposed and delt with so urethane will adhere properly,, my job is to do a proper install, the adhesive manufacturer’s job is to make and sell a automotive urethane that will stick to a properly prepared pinchweld regardless of how much old urethane is on it.. there is a LOT more to an install than how much urethane is still left on the pinchweld, it really bugs me for a broad big picture statement to be said by non installing people on how to use an install product, adhesive or whatever it is… it just isnt that simple.. ive installed hundreds of pieces of glass with NO old adhesive left on a properly prepared pinchweld … all you 20 and 30 year experienced techs know what that is all about.. safety first..

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