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  1. #1
    Join Date
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    Default Adhesive for plastics

    Does anyone have any experience with an adhesive for plastic? - I have a Mercedes bumper bar which I need to repair - Material unknown -car is an E220

  2. #2
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    Normally bumper bars are welded, the propper gear is expensive for a one off, many companies out here that will do on site repairs. You may get away with a Soldering iron and filler although that is a really hit and miss method.

  3. #3
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Alf Scotting View Post
    Does anyone have any experience with an adhesive for plastic? - I have a Mercedes bumper bar which I need to repair - Material unknown -car is an E220
    Car bumpers are commonly made of plastics like Polypropylene (PP) which most conventional adhesives and even standard bog are near useless at sticking to.
    To further complicate matters the coatings use to cover bumpers don't play nicely with adhesives. Even adhesives that appear at first to stick will eventually become undone by the (wind/road/motor) vibrations involved in a motor vehicle. This is why adhesive repairs are rarely performed and the bumpers are usually replace.

    If its a thickish flatfish plastic panel a mechanical repair ie metal plate behind and SS counter sunk screws that can along with visible cracks be bogged over might be acceptable but may also eventually fail with cracks developing between holes and along original cracks..

    PP can be welded but unless you know what you are doing plastic welds can end up looking awful, and the area around the weld can buckle. Just like adhesives and mechanical repairs welds may not last as the weld becomes a stress point and repeated vehicle vibe will end up breaking it again.

  4. #4
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    Plastics have changed drastically over the past few decades, because manufacturing systems have become more sophisticated.
    The incorporation for example of glass and or carbon fibres makes those plastic parts impossible to weld or glue. As was already said, external mechanical reinforcing is the only way. There are flexible bumper bar fillers available, e.g. at Repco or specialist automotive paint places. I've used them on bumpers with deep scratches and gouges successfully.
    PVA parts without fibre reinforcing can be successfully chemically welded, as good or better than new. Been doing that for decades. It takes special monomer catalyst liquid and polymerising powder.
    Heat welding with hot air and extruded filament filler is a good method for many thermoplastics (plastics that will remelt with heat), but not thermosetting plastics (plastics that start "molten" and then set hard for good. They will disintegrate or burn with heat after that).
    Cheers, Joe
    retired - less energy, more time to contemplate projects and more shed time....

  5. #5
    Join Date
    Oct 2020
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    Greendale Vic. Australia
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    Default Epoxy resin

    I've repaired plenty of motorbike plastics and RC Aircraft using Zap Cyano first to align things, then West Systems Epoxy resin 105 and glass cloth or mat. front and back.
    Everything has to be thoroughly roughed up to give a 'tooth' for the resin. (Forget Polyester resin, it's useless for most things... maybe swimming pools!)
    In 'stress' areas sometimes I'll use a 2-3mm drill and insert CF or similar rod through at opposing angles after the first Glass coat and before the final.
    Then there's the filling and painting...

  6. #6
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by joolstacho View Post
    I've repaired plenty of motorbike plastics and RC Aircraft using Zap Cyano first to align things, then West Systems Epoxy resin 105 and glass cloth or mat. front and back.
    Everything has to be thoroughly roughed up to give a 'tooth' for the resin. (Forget Polyester resin, it's useless for most things... maybe swimming pools!)
    In 'stress' areas sometimes I'll use a 2-3mm drill and insert CF or similar rod through at opposing angles after the first Glass coat and before the final.
    Then there's the filling and painting...
    Motor cycle and RC plastics are often using something different to car bumpers. I think it might be ABS or PVC or similar.

    Last year at night, despite a rear camera, I manage to back our then new 4W into a black car parked on the other side of the road. I wasn't going very fast and just heard a light bump. and hit the brake. I pulled forward about a meter and got out to inspect the damage fearing the worst. I was just in time to see the bumpers on both cars had been pushed in about 100mm but in front of me they both "self healed" as they popped back out again to their original shape. There was a tiny scratch on the black car and nothing on ours. A year on there are hairline cracks in the paint around the border of the dent on our car but you have to look closely to see them.
    Last edited by BobL; 29th Sep 2022 at 08:54 AM.

  7. #7
    Join Date
    Sep 2005
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    Default

    There are specific fillers made for plastic auto bumpers they are really only for filling holes in the bumper.

    https://www.isopon.com/aus/en-aus/pr...plastic-bumper

    If the plastic has a split in it the normal process for stitching it together ready for filling is with staples that are embedded into the plastic.

    https://www.vevor.com.au/stud-welder...iABEgK_T_D_BwE

  8. #8
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    Specialty adhesives for bonding low energy plastics like polypropylene and polyethylene do exist.
    3M make a couple of these which I have used successfully to repair PP bumpers where welding has been impractical.
    Try 3M™ Scotch-Weld™ EPX DP 8010 for a start.
    Förch also make make one called 2K-HA, K152 which looks on paper to be comparable to the 3M product.
    Hot stapler clips (search for them on eBay) are also very useful for strengthening repairs.

  9. #9
    Join Date
    Oct 2004
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    Southern Highlands NSW
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    Default

    Dented plastic "bumpers" can often be popped back to original shape with application of hot air gun.
    Method is to warm it up over the dent and around it until it's soft enough to be pushed back with a gloved hand, assuming you can get behind it.
    Scratches probably remain to be filled and painted.

  10. #10
    Join Date
    Sep 2012
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    York, North Yorkshire UK
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    Hi Guys,

    An accident and body repair shop in the same yard as one of the Engineering places that I visit has a skip almost full of plastic car body parts, maybe 8 tons or so. I did ask what becomes of them, they told me that they are sold to a plastics recyclers. At one time they just went to the tip/landfill. They are not allowed to do that any more. Any damaged panels are simply removed and replaced. Most if not all seem to be glued in place rather than nuts and screws. Even our general domestic waste goes to an incinerator electricity generating plant. They actually built two of them on the same site !
    Best Regards:
    Baron J.

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