# Repairing Plastic



## Les (Feb 5, 2012)

This isn't really directly related to what we do, but I have a project where I need to repair some plastic which has cracked all the way through in some places. 
It is actually the case of a synthesizer. The plastic is kind of a fiber-like substrate, as it doesn't have much bend to it. Once I strip the keyboard down, I should have access to both sides, but I was wondering what the best way to go about the repair would be. 

I was thinking JB Weld. What I would do is use a Dremel tool to carefully "trace" the cracks (not going all the way through), much like what you would do with an angle grinder if you were actually going to weld metal. Then, I would use a plastic "patch" on the bottom (concealed) side, at least twice as wide as the affected surface. I would bond the patch to the surface by first roughening up both sides and applying JB Weld. After that's cured, I would turn the piece over, and fill the Dremel'd gap. Once that's cured; sand/sculpt, prime, and paint. 

I was talking to my dad about it and he suggested looking in to a Bondo product that is almost like fiberglass as it has fiber in it and is supposed to be very strong (this would be used instead of the plastic patch on the bottom). Then JB Weld the top like usual. 

My concerns are that JB Weld doesn't bond to all plastics, and I don't know what kind of plastic this is. I don't think it's polystyrene or polyethylene (which JB Weld recommends against), but I really have no idea. 
I was also thinking of 2-part epoxies like in the double-syringe tubes, but my problem with it is that it's not a filler like JB Weld is. 

Here are some pictures of what I'm up against. Any suggestions?










As you can see, some areas are quite cramped, while others are fairly workable. Luckily, the worst crack has plenty of room under and around it (first pic). Others will take patience and precision. I have one of those, but not much of the other. Not telling which one  .

From what I've seen, all these cracks go all the way through. Oh yeah, and I don't have the money to invest in a plastic welding kit  . I'd rather try to stick to epoxies, etc (no pun intended).


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## howlingwolf487 (Feb 5, 2012)

Les,

I see no reason why super glue wouldn't work in this case (no pun intended). Go for the "gel" type so it doesn't run into the electronics. Stay away from Gorilla Glue, as it expands when curing. I personally recommend Loctite's version from using it myself for similar fixes. You'll need to find some way for the edges of the crack to stay lined up while the glue is curing...some judiciously-placed small weights may help.


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## techieman33 (Feb 5, 2012)

Harbor freight has a plastic welding kit for $20
Plastic Welding Kit 80 Watt Iron


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## Theresa (Feb 5, 2012)

I find that I'm turning to Sugru more and more for all kinds of repairs Outdoor types | sugru | Hack Things Better


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## shiben (Feb 5, 2012)

Theresa said:


> I find that I'm turning to Sugru more and more for all kinds of repairs Outdoor types | sugru | Hack Things Better


 
That looks pretty sweet. However, I personally think super glue will be the best choice here for your small cracks, and that Sugru might be best for the larger cracks. I dont know that the plastic is going to weld nicely, often you need to use microwaves not just plain heat to make it work correctly, also I dont believe all plastics can be welded, and if thats so this probably isnt one of them... The Sugru stuff is cheap, try picking some of that up along with some liquid super glue. The gel is ok, but as long as your cracks are pressed together tightly, the glue will actually propagate better thru the tight crack than a loose one as long as its viscous enough. Sort of like soldering brass.


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## gafftaper (Feb 5, 2012)

I'm another vote for good old superglue. If you can get inside, to protect the electronics I would use the liquid as it will soak into the crack really nicely. Your JB Weld approach, while it might work fine, is way too much effort. The superglue is a simple solution and it will seal the crack together really nicely.


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## jonliles (Feb 7, 2012)

What's the model of the keyboard? Maybe you can by a bad one on eBay/Craigslist for parts and transfer good parts to good case?


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## josh88 (Feb 7, 2012)

It's real interesting Les that I just got rid of a Kurzweil a month or 2 ago that had cracks in similar places from what I can tell. Almost thought you had mine somehow.


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## shiben (Feb 7, 2012)

If you want to harden it, spray it with bed liner after its fixed. That stuff seems to be nearly indestructible.


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## josh88 (Feb 7, 2012)

shiben said:


> If you want to harden it, spray it with bed liner after its fixed. That stuff seems to be nearly indestructible.


 
Not that Mythbusters is the pinnacle of science but they essentially bomb proofed things with bed liner, they did show that it added a significant amount of resistance to wood and also cinderblock walls coated in it. It sold me on the protective properties of that stuff.


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## shiben (Feb 9, 2012)

josh88 said:


> Not that Mythbusters is the pinnacle of science but they essentially bomb proofed things with bed liner, they did show that it added a significant amount of resistance to wood and also cinderblock walls coated in it. It sold me on the protective properties of that stuff.


 
I saw another show where they were discussing cheap ways for Israelis to harden their houses, a couple coats of bedliner ended up being able to resist a medium sized improvised car bomb parked a short distance away. I doubt it would stop an RPG or other anti-tank round, but it would certainly protect a keyboard from cracks and dings.


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## Les (Feb 10, 2012)

josh88 said:


> It's real interesting Les that I just got rid of a Kurzweil a month or 2 ago that had cracks in similar places from what I can tell. Almost thought you had mine somehow.


 
Dude, we are way too similar!

It is an old K2000 V3. I bought it to complement my K2600XS (actually, I bought it so that I wouldn't have to haul the K2600 to *every single practice/jam session*). I hope to get in to community theatre pit orchestras one day when I get better/have the time. Kurzweil's have some sweet orchestral sounds and I'd love to experience theatre from another angle. What type of Kurz did you have, by the way?

To everyone else: thank you all for your suggestions on this! I actually ended up using a combination of Devcon 5 minute epoxy and synthetic window screen (internally). It worked very well, but gafftaper, you were right. It was a lot of effort and I should have just done Super Glue. 

I then sanded the outsides of the repaired areas down with #220 grit sandpaper and Dremeled any areas that were too high or rough. Then, I coated the whole thing with Rustoleum 2-in-1 high-build primer and resanded. Finally, a few coats of Rustoleum "Textured Black" spray paint. I am very happy with the results, and while some of the repairs are still visible, they feel sturdy and I don't think I will have any issues. 

I do like the idea of bedliner -- too bad I'm just now catching up on this thread! I once sprayed the frame of a homemade projector screen with bedliner and it made an awesome finish. I'm determined to use it again somehow. 

Anyway, here are some pics of the process and finished product!





























By the way, anyone know anything about buttons? I'm having a weird issue with a few of them.


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## jonliles (Feb 10, 2012)

Sometimes they need a good cleaning...gunk gets under the contacts. I usually pick up a can of the Red Contact Cleaner at Guitar Center (Brand name escapes me). If it is a leaf spring switch and you can remove the button cap, I would rub each spring beteen 2 papertowels doused with the contact cleaner. It work for my TL2448.


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## josh88 (Feb 10, 2012)

The one we had was an old K250, ended up donating it to somebody I believe, can't honestly remember where it went. Looked like this:


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