FAQ > Windshields > Windshield Repair 101
Windshield   Construction    -   Windshields   are   Laminated,   usually   in   three   layers.            The   two   layers   of   glass   are separated   by   a   layer   of   tough,   flexible   plastic.      A   clear   windshield   has   no   coloring   in   the   laminate   at   all.      A   tinted windshield   on   the   other   hand   has   a   uniform   color   to   it.      The   shaded   windshield   is   tinted   and   has   a   darker,   visor band.      The   tint   or   shading   is   usually   done   by   applying   dye   to   the   plastic   inner   layer.      Glass   repair   is   typically   only performed   on   windshields   and   a   very   few   back   glasses   because,   as   a   norm   all   the   other   glass   in   the   average   vehicle is   made   of   tempered   glass.      Your   door,   vent,   quarter,   and   and   most   all   rear   window   back   glasses   are   made   from tempered   glass   that   is   hardened   by   heating   and   cooling   which   makes   it   extremely   brittle   so   that   it   shatters   into small pieces when it’s damaged, so it cannot be repaired.
Why   The   Windshield   Cracks    -   Understanding   windshield   repair   begins   with   understanding   how   a   windshield   is   damaged.   The   severity of   damage   that   can   be   repaired   is   more   than   a   surface   pit   but   less   than   shattered   glass.      When   an   object,   such   as   a   stone,   hits   the windshield   at   high   speed   a   pit   is   created   on   the   outer   glass   surface.      Part   of   the   surface   glass   is   basically   pulverized   by   the   object.      The ground   glass   appears   white   on   the   surface   of   the   windshield.      If   the   pit   is   just   white,   with   no   visible   cracks   coming   from   it,   it's   only surface   damage,   and   usually   poses   no   threat   to   the   windshield,   but   if   the   pit   appears   black   or   silver,   there   is   a   crack   with   an   air   cavity beneath   it.   The   impact   may   have   also   caused   a   small   cone   of   glass   to   separate   from   beneath   the   surface   of   the   outer   glass.      There   may be more air cavities underneath the separated cone.
The   concern   with   air   cavities    is   that   the   air   will   eventually   expand   and   separate   or   crack   the   glass.   Air,   like any   gas,   expands   with   heat.       Most   people   link   cold   weather   to   cracking,   but   cold   actually   causes   the   air   in   the damage   to   contract.       Then   when   the   heater   or   defroster   is   turned   on   it   is   like   blowing   up   a   balloon.      Air   expands to   a   point   where   the   glass   can   no   longer   contain   it.      The   air   separates   or   cracks   the   glass   to   make   room   for itself as it continues to expand. The   primary   objective   of   windshield   repair    is   to   restore   the   structural   integrity   of   the   windshield.   While   the windshield   repair   process   usually   results   in   a   much   better   appearance,   restoring   structural   integrity   is   the   main   reason   for   doing   a   repair.     There   will   still   be   some   evidence   of   damage   after   the   repair.      If   you   want   the   damage   to   totally   disappear,   you   must   replace   the windshield.      And   of   course,   if   the   damage   is   in   the   driver's   view   of   the   road,   the   windshield   must   be   replaced.      One   example   of   a   post- repair   blemish   occurs   when   the   shaded   area   of   the   windshield   is   damaged.      Air   leaks   in   and   bleaches   the   dye   in   the   laminate   at   the damage   site.      When   the   repair   is   finished,   the   outline   of   the   damage   can   be   seen   easily   from   inside   the   vehicle,   because   of   this   bleaching process.      But   if   the   repair   is   done   right,   the   integrity   of   the   glass   structure   will   be   sound.      Windshield   repair   prevents   damage   from spreading   to   the   point   where   glass   replacement   becomes   necessary.      To   stop   the   damage   from   spreading,   ALL   the   air   must   be   taken   out of   the   damage.      If   air   remains   in   the   tips   of   a   star   break   damage   for   example,   it   is   not   a   good   repair.      Getting   all   the   air   out   may   require drilling extra holes in the tips of the star.  This would not be done if appearance was the main objective.
Finding   the   air   spaces    -    The    first   step   in   making   a   windshield   repair   is   to   determine   where   the   air   spaces   are.      The   air   spaces   can   be   in one or more locations.
Air   In   The   Separated   Cone   -    Sometimes   the   size   or   force   of   the   object   hitting   the   windshield separates   a   cone   of   glass   and   then   cracks   or   even   crushes   the   cone   as   it   is   pressed   into   the   plastic   layer.     This   leaves   an   air   space   in   the   cracks   of   the   cone.      The   pit   on   the   surface   of   the   windshield   is   usually much larger in this type of damage (see figure 7) .
The   Need   For   Drilling   -    It   is   often   necessary   to   drill   the   glass   to   release   trapped   air.      If   you   don't   have   access   to   the   air   space, or if you have only limited access, trying to replace the air with resin is like trying to fill a bottle without removing the cap.
Windshield   Repair   Equipment   -    All   windshield   repair   systems   work   on   the   same   principle   -   the   air   is   replaced   with   clear   liquid   resin.     Windshield   repair   equipment   comes   in   kits   often   contained   in   a   case   for   taking   to   remote   locations.      There   are   several   different   systems available.      Most   of   these   systems   use   some   kind   of   pressure   or   vacuum   method   to   draw   out   the   air   before   injecting   clear   resin   into   the air   cavity.   Another   method   that   requires   drilling   into   the   air   space   and   allowing   the   resin   to   simply   flow   into   the   cavity.   This   method would   require   the   break   to   be   completely   open   to   easily   accept   the   resin   through   capillary   action.      It   can   work   but   if   the   resin   doesn’t flow   into   the   break   your   one   chance   at   making   a   good   repair   is   gone.      It's   very   important   to   use   the   right   equipment   the   first   time around   because   you   only   get   one   shot   at   repairing   a   break   in   a   windshield.      Once   it's   been   done   and   the   resign   hardens   it's   over   and cannot be repaired again.
Here at Phoenix Glass in Knoxville TN. we use AEGIS windshield repair equipment because we feel is the best equipment in today’s market.
Pressure injector tool Repair resin Drill with carbide drill bits Single-edge razor blades Ultraviolet (UV) light
Pressure   Injection   Type   Tools   -    Pressure   injection   tools   usually   use   a   combination   of   pressure   and   vacuum   to   help   the   resin   flow   into the   air   spaces.      The   repair   fixture   tool   holds   a   chamber   with   an   O-ring   seal   to   the   glass   surface   during   the   repair.      The   process   usually creates   a   vacuum   by   unscrewing   the   injector   piston   followed   by   screwing   the   injector   piston   down   to   create   pressure   to   the   point   where windshield   repair   fluid   is   just   short   of   beginning   to   seep   from   the   perimeter   of   the   O-ring   seal   on   the   glass   while   carefully   observing   the crack   legs.      These   types   of   units   typically   do   not   have   any   type   of   vacuum   or   pressure   indicator   to   go   by   other   than   sight   so   it's   possible (in   our   opinion)   to   not   obtain   enough   vacuum   and   to   unknowingly   inject   to   much   pressure   which   coud   possibly   cause   the   laminate   to separate and or make the breaks crack legs run out farther.
Aegis windshield repair kit Before and after views of a windshield repair
Air   Beneath   the   outer   layer   of   glass    -    One   location   for   an   air   space   is   between the   separated   cone   of   glass   and   the   outer   glass   (see   figure   4 ).       This   air   space   appears black when viewed from directly above the damage (see figure 3).
Air   Between   the   Plastic   And   Outer   Glass   Layer   -    The   separated   cone   of   glass   may   also   press   into the   plastic   layer,   which   begins   to   break   down   the   bond   between   the   plastic   and   the   outer   glass   around the   perimeter   of   the   damage.      This   separated   area   becomes   another   air   space   in   the   damage   (see   figure   5) .     This air space appears milky when viewed from directly above the damage.
Air   In   The   Outer   Glass   -    If   the   object   hitting   the   windshield   creates   any   cracks   in   the   outer   glass, there's   also   an   air   space   in   the   outer   glass.      This   air   space   may   be   located   at   the   surface   of   the   outer glass   or   on   the   bottom   side   of   the   outer   glass,   or   both   (see   figure   6).    These   air   spaces   will   look   black   or silver.
Windshield Repair 101 Questions   regarding   Windshield   Repair   are   a   common   place   for   our   Customer   Service   Representatives   on   a   daily   basis.      This   page   will explain   some   of   the   need-to-know   basics   about   windshield   repair.      It   is   not   a   how-to   article   and   it's   intent   is   not   to   list   procedural   steps, or   to   focus   on   any   one   repair   system,   but   to   describe   what   windshield   repair   is   designed   to   do   and   what   the   focus   should   be.      These basics   can   be   applied   to   any   system   of   windshield   repair.       There   are   several   Myths   about   windshield   repair   which   can   lead   to   a   great   deal of   confusion.      Glass   "repair"   and   "replace"   are   often   used   interchangeably.      A   lot   of   people   are   not   aware   that   glass   can   be   repaired.     Some   people   who   have   never   seen   a   windshield   repaired   compare   it   to   placing   a   bandage   on   the   glass.      Others   expect   the   result   to   be flawless   with   no   evidence   of   damage   remaining.   The   truth   is   somewhere   between   these   two   extremes.      As   more people   begin   to   understand   that   a   windshield   is   a   structural   part   of   the   vehicle   there   has   been   a   bit   of   a controversy   on   the   size   or   type   of   windshield   damage   that   can   be   repaired,   and   when   replacement   is   the   only choice.     Technicians   have   been   repairing   spot   damage   in   windshields   for   over   30   years,   and   those   who   have   been in   the   business   that   long   don't   see   why   there   should   be   any   controversy.      Windshield   repair   is   not   only   about whether a repair can be made or how it will look after the repair, but also routine windshield maintenance.
A windshield break air cavity Windshield Construction Air beneath the outer layer of a windshield break The air space in the windshield break appears milky An air space located beneath the surface of the windshield glass Air in the seperated cone of a windshield break
Some of the more common pieces of equipment in windshield repair kits include:
Syringes or eye droppers Glass cleaner Magnifying glass Suction Cup Mirror Probe
The air space in a windshield break usually appears black Phoenix Glass Knoxville's Finest Windshield and Auto Glass Replacement Center 947.5706
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