Mending Plastic

JHZR2

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Polypropylene and Polyethylene are difficult to repair. If they need to be repaired, most any redly available product will NOT do the job, including most typical epoxies. Two years or so ago, I ran over a retread abandoned in the middle of the interstate mad in my 135i. Fortunately no real damage, but did get a few cracks in the belly pan. They were pretty minor, so Ive left them, but since I had the pan off for some other service, I figured Id try fixing them... The right product for these difficult plastics, is this 3M adhesive, #8005. I have this from another repair I did a year or more ago, and its still good. Some pics of the damage: Note, I had already scuffed it with some sandpaper. I got some paint scrapers from Home Depot, and cut them to fit as backers for this repair. I wasn't going to try to fix the cracks with adhesive, as there isn't enough surface. I figured Id work a little in for the repair, but nothing else. Of course both sides get scuffed: I did a flame treatment again to enhance the surface radical activity to promote better bonding: Mix that stuff up, it gets gritty... I wasn't really trying to do the neatest job... The panel was still functional when cracked and if I get another one, then Ill get another one. Plus, this stuff sets up fast - faster than I recalled last time I used it. Doing more, smaller batches is advisable... I just wanted to see how this would work... Time will tell. I wanted some excess on the surface to work into the crack, since the plastic pieces didn't cover all of the cracking, and the one crack had a long length at the raised profile of the plastic, where I couldn't back or support it, so I figured mass was the best approach. it will be interesting to see how this works out...
 
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That's an interesting find. The technical data sheet contained this: "Contains 0.008” glass beads for bondline thickness control". I didn't know they did that. Thanks for posting.
 
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Some pop rivets with backing washers would provide additional strength, if applicable to your project.
 

JHZR2

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Originally Posted By: doitmyself
Some pop rivets with backing washers would provide additional strength, if applicable to your project.
I do have a rivet gun someplace... Thats a great idea! But Im not familiar enough to know about backing washers... Is that a specific type of rivet, that has these as part of the assembly, or are you saying to take some washers (which would need to have really small center holes), and rivet them as part of the "sandwich"? The fix is on the inside, so it can't be seen by an onlooker. Rivets would ensure notionally that the fix is still in place, if I place them right that the rivet would fall out if it fell apart... Thanks!
 
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JHZR2

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Got it, thanks... I've only used rivets once, for connecting two pieces of sheet metal together, where it was good enough... I'll check my ace hardware tomorrow am...
 
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Thanks for posting! Always looking for ways to replair plastic + hard-to-bond plastic in particular. Been reading up on plastic "welding" as well. Very interesting. Read where one guy used wire screen as a backer, then melted plastic into it from the original piece as well. When cooled, it was literally "melted together." Makes sense. Another one I read where the guy melted wire into the joint to reinforce it using a battery. Could also use a constant-current bench supply. Keep us posted!
 

JHZR2

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I got some aluminum washers and 3/16 rivets. Ace had the washers and rivets, I might have considered stainless, but figured everything else under the car is Aluminum. Drilled the holes and popped them in. Did the first one backwards so ground off the pop part to be flush with the washer. Only needed to use a washer on one side.
 
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I had to fix the door handle snap on the volvo last weekend.. We just ended up using a 2 part epoxy.. Looking back, it might have made everything stick better if I lightly hit it with a torch to rough the surface. I am writing down that 3M number for sure.
 

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The only problem for stuff you'll see, is the grittiness. Not sure if they make one without solids... Maybe white or clear...
 
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Bad advice on those pop rivets. Now we won't know how good or bad your glue is! You should at least glue another patch somewhere else and then try to pop it off later.
 

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Lol, I think I'll take that scenario... I think I'll see if the remnant glue loses its tack.
 
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