FAQ > Collision Related Auto Body Windshield Pinchweld Repair
What are the requirements for properly preparing a vehicle's pinchweld prior to installing an adhesive bonded windshield, side or back glass? The   answer   to   your   question   would   depend   on   the   situation   the   vehicle   is   in.      If   the   vehicle   is   under   going   a   routine   auto   glass installation   the   answer   goes   in   one   direction   but   if   the   vehicle   is   undergoing   body   work   that   affects   any   of   the   pinchweld   areas   that   the glass   bonds   to   it   goes   in   another.      The   easiest   way   for   us   to   go   there   is   to   tell   it   all   so   that   in   whatever   situation   you   find   yourself   you   will know   the   proper   procedure.      This   answer   is   rather   detailed   so   in   an   effort   to   give   the   most   accurate   answer   that   we   could   we   went outside the box to I-Car. Auto Glass Pinchweld Treatment The Wrong Step Can and Will Add A Weak Link
A   urethane   bonded   back   glass   contributes   to   the   structural   integrity   of   a   vehicle   just   as   much      as   the   windshield.     Pinchweld   flanges   that   hold   stationary   glass   require   proper   treatment   during   repairs   to   insure   proper   bonding   of the   glass   and   to   maintain   the   structural   integrity   of   the   vehicle.      Stationary   glass   in   vehicles   today   add   to   the structural   strength   and   rigidity   of   the   vehicle   body.      If   the   glass   is   not   properly   bonded   to   the   flange,   it   can   alter how   the   structure   reacts   in   a   collision   or   even   during   normal   body   flexing   and   driving.      The   deployment   rate   of an   air   bag   can   be   altered   by   fractions   of   a   second,   where   fractions   count,   resulting   in   slightly   early   or   delayed deployments.      Although   the   windshield   is   usually   referenced   when   discussing   maintaining   vehicle   strength   and structural   integrity   during   glass   installation,   proper   treatment   of   pinchweld   flanges   also   extends   to   the   back   lite   and   urethane-bonded side   glass   as   well.      The   focus   on   this   page   is   the   procedures   and   concerns   that   technicians   must   be   aware   of   when   performing   both collision repairs and glass replacement as it relates to pinchweld flange areas.
During collision repairs pinchweld flanges become an issue for one of two reasons. 1 . The glass is broken, requiring replacement. 2 . The pinchweld flange the glass bonds to will be disturbed due to repairs or panel replacement. Different   recommendations   exist   for   the   pinchweld   flange   when   the   flange   is   involved   in   body   repairs   or   panel   replacements,   compared to when just the glass is being replaced.
Glass Replacement Only When   replacing   the   glass,   and   the   pinchweld   flange   does   not   require   repair   or   replacement,   the   existing urethane   adhesive   bead   should   be   left   intact   until   glass   installation   is   started.      This   also   applies   to   pinchweld on   the   sides   of   the   opening   away   from   repairs   or   panel   replacement.      The   reason   that   the   urethane   is   left intact   until   the   glass   is   to   be   replaced   is   to   protect   the   base   of   the   bead   from   contamination.      Some   sources even   say   that   it's   acceptable   to   prime   or   paint   over   the   existing   bead   of   urethane   during   repairs,   since   it   will   be cut   away   when   the   glass   is   ready   to   be   installed,   exposing   a   clean   fresh   surface   for   bonding.      Most   vehicle   and adhesive   makers   recommend   cutting   out   the   glass   as   close   as   possible   to   the   glass,   leaving   the   original urethane   bead   as   thick   as   possible    (see   Figure   2) .   Then   when   it's   time   to   start   installing the   replacement   glass,   trim   the   existing   urethane   bead   to   a   thickness   of   1-2   mm   (see   Figure   3).      This   is   a   full- cut   out   method   of   installations,   even   though   all   of   the   adhesive   is   not   being   removed.      Performing   this   final   cut out   just   before   installing   the   glass   ensures   that   a   clean,   uncontaminated   surface   exists   for   bonding.      Leaving   1-2 mm   on   the   pinchweld   not   only   helps   prevent   scratching   the   pinchweld   with   the   cut   out   knife,   it   also   helps   to ensure that the new bead will be located in exactly the same location and size area as the original installation.
Pinchwelds In The Repair Area
If   the   pinchweld   flange   will   be   disturbed,   for   repairs   such   as   replacing   a   roof   skin,   attention   to   proper   repair procedures   are   especially   important   (see   figure   4).      This   includes   using   the   proper   weld   method,   and duplicating   the   number   and   spacing   of   original   welds.      The   structural   integrity   and   rigidity   of   the   glass opening   can   be   altered   by   the   use   of   incorrect   repair   and   installation   methods.   Once   the   panel   replacement   or repair procedures are complete, the pinchweld flange area must be properly prepared.
PINCHWELD PRIMERS Pinchweld   primer   is   the   black   primer   that   is   applied   to   the   flange   area   before   laying   down   the   urethane   adhesive.   The   use   of this   material   is   often   not   fully   understood   as   it   relates   to   the   total   installation.      Pinchweld   primer   is   a   primer,   and   like   any primer,   is   designed   as   a   link   for   adhesion   between   a   substrate   and   some   other   material.      The   substrate   that   pinchweld primer   is   designed   to   bond   to   is   OEM   paint   finishes   and   some   repair   paint   coatings   such   as   approved   epoxy   and   self-etching primers.      The   other   material   pinchweld   primers   are   designed   to   bond   to   are   the   urethane   adhesives   in   the   same product   maker's   system.      Although   suggested   for   use   over   small   spots   of   bare   metal,   pinchweld   primer   is   not   a full   corrosion-protections   package.   It   provides   chemical   linking   between   the   substrate   finish   and   the   adhesive   that it's   designed   to   be   used   with.      Leaving   the   pinchweld   primer   out   of   the   process   can   cause   adhesion   failure   between the adhesive and the flange.
Guidelines For Pinchweld Primer When   using   pinchweld   primers,   some   criteria   needs   to   be   followed   or   considered   to   allow   the   primer   to   fully   provide   the   special   chemical link   it's   designed   for.      These   are   guidelines,   and   are   not   intended   to   replace   product-specific   or   vehicle-specific   recommendations   for proper   glass   installation.      Use   only   the   recommended   primer   for   the   adhesive   to   be   used.      Do   not   mix   systems,   as   chemistries   may   differ and   failures   can   occur.      Inside   of   any   one   adhesive   maker's   product   line,   multiple   primers   may   exist   for   use   with   different   adhesives.     Check   the   shelf   life   of   the   primer   to   ensure   it   has   not   expired.      Even   though   the   primer   is   unopened,   it   could   be   out   of   date.      Once opened   the   primer   will   have   a   limited   time   period   for   use   before   it   should   be   properly   disposed.      The   container   should   not   be   left   open   to the   air,   as   this   greatly   reduces   its   working   life.      Many   primers   use   an   inner   cap   and   an   outer   cover   to   help   seal   the   material   from   the   air.     Some    adhesive    makers    now    offer    a    one-time    use    cartridge    applicator    to    help    with    this    problem.        Follow    the    product    maker's recommendations   for   application.      This   will   ensure   the   correct   thickness   is   obtained.      Directions   may   be   so   specific   as   to   state   which direction each coat is to be applied relative to the previous coat.
Do   not   apply   the   pinchweld   primer   on   top   of   any   remaining   original   adhesive   that   has   been   trimmed   to   the   proper   thickness.   This   can lead   to   a   weaker   bond   when   the   new   adhesive   is   applied.      Apply   the   pinchweld   primer   to   OEM   paint   finishes   or   on   areas   where   approved primers   have   been   applied.      The   glass   adhesive   should   only   be   placed   where   there   is   pinchweld   primer   or   an   original   properly   trimmed bead   of   urethane.      Respect   the   recommended   minimum   and   maximum   dry   times   before   applying   the   urethane   adhesive.      The   primer needs to dry long enough to let solvents escape, however if maximum times have elapsed the primer may need to be reapplied.
PINCHWELD FLANGE CONDITIONS Some of the conditions that may exist in the glass pinchweld area include corrosion, scratches, dirt, and loose adhesive or sealants.
Scratches Scratches in the finish can occur no matter how careful the technician is. Take   special   care   to   prevent   any   type   of   scratch   to   the   pinchweld   that   breaks   the   OEM   finish   during   both   glass   removal   and   collision repairs.      Most   glass   adhesive   systems   recommend   using   pinchweld   primer   to   cover   scratches,   providing   the   scratches   don't   exceed   some size   limit.      Pinchweld   primers   are   designed   to   gain   adhesion   between   the   paint   coatings   and   urethane   adhesives,   not   to   bare   metal.   The best recommendation is to properly apply a recommended epoxy or self-etching primer to pinchweld scratches.
ALUMINIUM PINCHWELDS Aluminium   pinchweld   flanges   can   be   affected   by   using   the   wrong   type   of   glass   adhesive.      Vehicles   with   an   aluminium   pinchweld   may require   the   use   of   a   non-conductive   urethane   adhesive.      The   non-conductive   adhesive   may   also   involve   another   specialized   variable, referred to as "high modulus" (see below). If   a   conductive   adhesive   is   used   and   moisture   is   introduced   into   the   area,   it   can   pit   the   aluminium   through   a   process   of   electrolysis.      The electrical   current   comes   from   antenna   and   defroster   systems   in   the   glass.      As   more   electronics   are   installed   into   glass   for   navigation systems   or   cellular   phone   reception,   this   type   of   problem   is   likely   to   increase.      This   means   that   the   pinchweld   area   can   be   affected   by   the use of the wrong type of windshield adhesive.
CONCLUSION When   dealing   with   the   pinchweld   flange   area   of   a   glass   opening   it's   important   to   keep   the   following   points   in   mind:      Always   follow   the vehicle   maker   specific   guidelines   for   the   make   and   model   being   repaired.      Follow   the   adhesive   and   paint   maker's   directions   for   selection and   use   of   materials.      Respect   all   dry   times.      Prevent   breaking   through   the   OEM   finish   on   the   pinchweld   flange   whenever   possible.      No adhesive   can   stick   any   better   than   what   is   underneath   it.      And   when   dealing   with   structural   glass   this   can   become   alot   more   than   just   a water leak or an annoying wind whistle.
High-Modulus, Non-Conductive Glass Urethane Some   vehicles   today   have   glass   installed   with   an   adhesive   classified   as   high-modulus,   non-conductive   urethane.      Although   these   two terms are often combined into the same adhesive material, they refer to totally different and unrelated properties.
HIGH MODULUS High   modulus   refers   to   a   glass   adhesive   that   has   specific   physical   characteristics   after   it's   fully   cured.   Modulus   has   to do   with   how   much   pressure   or   stress   it   takes   to   get   the   urethane   to   deform,   stretch,   or   give.   High-Modulus   adhesive provides   a   high   level   of   rigidity   once   fully   cured,   usually   a   minimum   of   24   hours,   which   can   help   reduce   torsional twisting   or   stiffen   the   vehicle   body.      When   used   by   the   vehicle   makers,   it's   intended   to   improve   noise,   vibration   and harshness. Don't   confuse   high   modulus   with   "high   viscosity,"   which   defines   the   thickness   of   the   adhesive   at   the   time   of application.   Viscosity   is   a   scientific   term   used   to   compare   body   while   in   any   type   of   liquid   state.      The   higher   the viscosity   the   thicker   the   material.      Comparing   water   to   peanut   butter,   peanut   butter   has   a   much   higher   viscosity. Urethane   adhesive   used   to   install   automotive   glass   has   increased   in   viscosity   over   the   past   several   years.      High- viscosity   adhesive   allows   the   glass   installer   to   set   the   glass   into   the   adhesive   bead   without   it   sinking   or   sagging.   An adhesive can have a lower viscosity than another adhesive and still have a high-Modulus rating.
NON-CONDUCTIVE Urethane   adhesives   contain   carbon   which   can   conduct   electricity.      Non-conductive   urethanes   use   a   special   form   of   carbon   that   is   non- conductive.      On   certain   models   of   vehicles   with   antenna   grids,   defroster   grids,   and   other   electrical   systems   integrated   into   the   windshield or   back-lite,   the   vehicle   maker   specifies   use   of   a   non-conductive   urethane   adhesive.      This   is   to   ensure   that   there's   no   electrical   path   to the body through the adhesive bead.  This is of particular concern with aluminium-body vehicles.
During windshield replacement the urethane is cut as close as possible to the windshield leaving as much of the original urethane bead as possible on the pinchweld The existing urethane bead is trimmed to a thickness of 1-2 mm
If dealing with existing adhesive beads other than the original urethane, non-urethane substrates, bare metal, or non-OEM paint finishes, careful consideration must be given to compatibility with the replacement adhesive to be used and the integrity of the bond that will be formed.
Adhesives made for glass installation are designed specifically to chemically bond to the OEM urethane.
Using the wrong type of applicator can affect the performance of the primer. Usually   a   wool   dauber-type   applicator   is   specified   (see   Figure   6).      Wool   is   used   because   it   will   not   react with   the   chemicals   in   the   primer.      Using   an   acid   brush   or   shop   paper   towel   can   lead   to   contamination of   the   primer.      Shop   paper   towels   can   also   absorb   ingredients   out   of   the   primer.   Some   primers   are packaged   as   a   pen-type   applicator   to   help   eliminate   this   problem   and   provide   and   provide   a   convenient application system.
Usually a wool dauber-type applicator is specified.  Wool is used because it will not react with the chemicals in the primer.
Corrosion Corrosion must be removed, and the metal cleaned and protected, or it will re-occur (see Figure 7). This   will   cause   loose   adhesion,   water   leaks,   and   possible   structural   integrity   problems.   Brushing   or spraying   primer   of   any   kind   over   corrosion   without   removing   it   is   simply   buying   time   before   it   re- occurs.      Corrosion   that's   not   removed   may   also   provide   a   weak   link   in   that   area   and   allow   everything on   top   of   it   to   separate   from   the   pinchweld.      If   corrosion   is   in   advanced   stages,   with   thinning   metal occurring,   structural   integrity   must   be   carefully   evaluated.   Corrosion   must   be   removed   and   the metal   properly   treated   before   reapplying   any   type   of   body   primer.   Brushing   pinchweld   primer   over the   corrosion   spot   of   area   will   not   correct   the   problem.         Pinchweld   primer   should   be   used   over   the proper   corrosion-resistant   primer   only   after   proper   dry   times   have   allowed   all   solvents   to   escape   the primer.
Corrosion must be removed, and the metal cleaned and protected, or it will re-occur
Loose Adhesive And Dirt Any   loose   adhesive   or   other   loose   material   in   the   location   where   the   adhesive   will   be   applied   must   be removed   to   provide   a   solid   base.      Small   irregularities   in   the   surface   will   be   leveled   by   the   adhesive during   re-installation.      Dirt   must   be   cleaned   from   the   flange   area   so   that   all   products   can   gain   full adhesion.      It's   best   to   clean   dirt   from   the   flange   before   final   trimming   of   the   existing   urethane adhesive.      Avoid   solvents   when   cleaning   the   flange   area.      A   clean,   lint-free   towel   and   distilled   water is   recommended.      Avoid   tap   water.      Tap   water   can   contain   chlorine,   iron,   and   other   minerals   that might affect the bonding area.
Dirt must be cleaned from the flange area so that all products can gain full adhesion. The reason that top coats are not generally recommended on the pinchweld flange, where the adhesive bead will be located, is that all the solvents may not leave the finish for 60-90 days.  The urethane adhesive can be affected by these solvents. Another concern is that clear coat finishes are designed to resist chemicals and maintain a glossy finish.  This makes it more difficult to get the adhesive to stick to them. There is at least one vehicle maker who recommends finishing the pinchweld the same as the rest of the vehicle, top coats included but we do not have the information stating which manufacture this is.  Above all the best thing to do is follow the vehicle maker's recommendation. Removing a windshield with a cut out tool Pinchweld Primer is the black primer that is applied to the flange area before laying down the urethane adhesive.
FOLLOW RECOMMENDATIONS Makers of glass adhesives combine high-modulus and non-conductive into one adhesive because the vehicle models requiring one characteristic generally require both. This type of adhesive should be used to restore a vehicle to OEM specifications when service procedures specify or when the vehicle was made with it. Using high-modulus adhesive when it's not specified or when it was not designed into the vehicle could alter the vehicle, making it stiffer than original causing other potential problems.
Many    vehicle    makers    and    adhesive    suppliers    are    providing    guidelines    on    proper    cleaning    and    scuffing    for preparing   the   surface   for   epoxy   or   self-etching   primers.      Follow   the   paint   maker's   recommendations   for   proper application   of   the   approved   primer   being   used   on   the   flange.      After   the   proper   dry   time   and   before   applying   a topcoat,   the   area   of   the   flange   where   the   urethane   adhesive   will   be   applied   must   be   masked   off   (see   figure   5).     Some   paint   systems   may   recommend   doing   this   following   the   sealer   applications   rather   than   at   the   primer   stage.     The   flange   area   that   requires   masking   is   primarily   the   flat   portion   where   the   adhesive   bead   is   to   be   applied.      The area   beyond   where   the   bead   is   applied,   moving   out   of   the   flange   area,   should   be   top   coated   for   corrosion protection.  Primers must be fully dry, allowing all solvents to escape, before beginning the glass installation.
After the proper dry time and before applying a topcoat, the area of the flange where the urethane adhesive will be applied must be masked off.
Do Not!  use body filler on the pinchweld where glass urethane adhesive will be applied. Small irregularities in the flange surface will be filled when the adhesive bead is applied. 2.  Do Not!  Use “Spray Can Etching Primer” on the PinchWeld. It WILL NOT! dry to the point where the windshield Primer will not emulsify it.  There maybe some Brands out there that may work but in our experence we haven’t seen one.
Stop!
The   Typical   Spray   can   Etching   Primers   we   have   seen   used   have   never   worked.      “When   you   decide”   to   take   a   chance   and   use   them anyway   it   ends   up   costing   you   valuable   time   as   well   as   the   moneys   involved   in   materials   used   in   striping   the   pinchweld   surface   back down   to   the   bare   metal   surface   and   starting   over   again.      In   our   mobile   operation,   it   costs   us   a   second   trip   which   unfortunately   we   have to pass along to you in the form of a service fee adding even more expense.
I-Car , Glass Pinchweld Treatment I-Car , Glass Pinchweld Treatment
Almost all of the information on this page was taken from an I-Car article Dated March - April 2000.  You can see the original article at the link below.
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