Repairing an ancient plastic item - what's my best bet?
April 8, 2013 12:13 AM Subscribe
Can my elderly plastic piece be repaired by myself? What cements and/or techniques should I use?
Caveats
* I'm not trying to save time or money
* I'm not interested in sending the item to anyone, I want to do this myself to learn something...even "it's impossible"
* I'd really be most interested in hearing from someone who has successfully repaired an item like mine
Item
I have a large molded plastic piece from a car with numerous cracks and broken off bits, as well as some localized warping. The piece was molded in 1961 in England--the plastic is about 1/8" thick, and it is white in color. I have no idea what particular flavor of plastic it is, but it's not bakelite. (It looks and acts like styrene to me, but I have no way of knowing.) The environment the piece lives in is hot, it probably gets exposed on occasions to temperatures approaching 150F+...I mention this in case a repair material will fail if heated like this (for example, the adhesive on your favorite super-tape will stop working above 100F).
The plastic itself seems to be in decent condition; it might be a bit more brittle than it was new, but it's never been exposed to UV light and aside from being a punching bag for people with no sense of "is that too tight?" and some heat exposure, seems OK. I suspect a lot of the damage I describe happened the day it was originally installed...
This item will not be seen when it's done (it's hidden) but serves an essential role, and is an intricate shape which the relatively crude reproduction made today only approximates, making everything which has to happen after this piece is put on the car harder. I have one of these repros (which they now make out of fiberglass); I'll end up (reluctantly) using it if can't fix this.
Note that because of where the piece fits, I cannot glue backing material to it; it can't end up any thicker than it is, though it could conceivably gain tape or a very thin backer on the order of tape thickness.
Problems
The problems fall into three areas:
Cracks. There are numerous cracks at various stress points. All of them disappear when pressed back together. In the past I have tried putting typical hardware-store superglue in these type of cracks, but with very mixed results, and no confidence in the repair. Is there a cement which will work for this? It would have to be very liquid and able to be drawn in by capillary action alone... I can spread the cracks a bit, but not to the point of applying cement to either face and pressing them back together. I can get to the back of all of them to apply some sort of tape, if that's a potential solution. All of the tapes I have, from masking to Gorilla to duct tape, would fail in a short while in this environment, and my only tape thought was maybe something foil-backed might be strong enough.
Broken off bits. Fortunately these all are in a flat area where the piece is attached with screws to the car. I will be using large washers and a soft material between them and the piece for future preservation, but in the meantime, I need to get the missing chunks back into place. Can I buy sheet styrene, cut pieces to fit, and expect them to stay put if edge-glued (obviously cutting the original piece to match the repair shape as closely as possible? This is definitely an area which cannot have much extra thickness. This seems like an ideal place for a "welding" type glue, which chemically "melts" the pieces to each other and then sets, which is what I think normal plastic model cement does...but I think would be too demanding an application for Testor's or whatever. Plus--I think those type of glues require very specific knowledge of the type of plastic used...they will glue, say, only ABS.
Localized warping. This I am concerned least about, but some long flat edges have a wave in them from years of having screws placed every six inches and no support between. This would be fine to leave as-is, but am curious if there is a way to fix this. I was thinking very careful use of a heat gun and a flat backing piece, or two flat pieces to press the heated material between. I know this is a potential disaster without great care, so may skip it...but am curious.
Thanks for any insight!
Caveats
* I'm not trying to save time or money
* I'm not interested in sending the item to anyone, I want to do this myself to learn something...even "it's impossible"
* I'd really be most interested in hearing from someone who has successfully repaired an item like mine
Item
I have a large molded plastic piece from a car with numerous cracks and broken off bits, as well as some localized warping. The piece was molded in 1961 in England--the plastic is about 1/8" thick, and it is white in color. I have no idea what particular flavor of plastic it is, but it's not bakelite. (It looks and acts like styrene to me, but I have no way of knowing.) The environment the piece lives in is hot, it probably gets exposed on occasions to temperatures approaching 150F+...I mention this in case a repair material will fail if heated like this (for example, the adhesive on your favorite super-tape will stop working above 100F).
The plastic itself seems to be in decent condition; it might be a bit more brittle than it was new, but it's never been exposed to UV light and aside from being a punching bag for people with no sense of "is that too tight?" and some heat exposure, seems OK. I suspect a lot of the damage I describe happened the day it was originally installed...
This item will not be seen when it's done (it's hidden) but serves an essential role, and is an intricate shape which the relatively crude reproduction made today only approximates, making everything which has to happen after this piece is put on the car harder. I have one of these repros (which they now make out of fiberglass); I'll end up (reluctantly) using it if can't fix this.
Note that because of where the piece fits, I cannot glue backing material to it; it can't end up any thicker than it is, though it could conceivably gain tape or a very thin backer on the order of tape thickness.
Problems
The problems fall into three areas:
Cracks. There are numerous cracks at various stress points. All of them disappear when pressed back together. In the past I have tried putting typical hardware-store superglue in these type of cracks, but with very mixed results, and no confidence in the repair. Is there a cement which will work for this? It would have to be very liquid and able to be drawn in by capillary action alone... I can spread the cracks a bit, but not to the point of applying cement to either face and pressing them back together. I can get to the back of all of them to apply some sort of tape, if that's a potential solution. All of the tapes I have, from masking to Gorilla to duct tape, would fail in a short while in this environment, and my only tape thought was maybe something foil-backed might be strong enough.
Broken off bits. Fortunately these all are in a flat area where the piece is attached with screws to the car. I will be using large washers and a soft material between them and the piece for future preservation, but in the meantime, I need to get the missing chunks back into place. Can I buy sheet styrene, cut pieces to fit, and expect them to stay put if edge-glued (obviously cutting the original piece to match the repair shape as closely as possible? This is definitely an area which cannot have much extra thickness. This seems like an ideal place for a "welding" type glue, which chemically "melts" the pieces to each other and then sets, which is what I think normal plastic model cement does...but I think would be too demanding an application for Testor's or whatever. Plus--I think those type of glues require very specific knowledge of the type of plastic used...they will glue, say, only ABS.
Localized warping. This I am concerned least about, but some long flat edges have a wave in them from years of having screws placed every six inches and no support between. This would be fine to leave as-is, but am curious if there is a way to fix this. I was thinking very careful use of a heat gun and a flat backing piece, or two flat pieces to press the heated material between. I know this is a potential disaster without great care, so may skip it...but am curious.
Thanks for any insight!
Without a picture or knowing what the shape of the object is, we can't advise you best how to proceed. For instance you may need to create an armature for the shape to help hold the parts while the cement dries.
Yes plastic cements work differently than adhesives and they come in different flavors...take a few bits in to a local hardware store (not a no-nothing big box home supply) and ask for the correct type.
Can you post a pic of a similar auto part?
posted by artdrectr at 1:29 AM on April 8, 2013
Yes plastic cements work differently than adhesives and they come in different flavors...take a few bits in to a local hardware store (not a no-nothing big box home supply) and ask for the correct type.
Can you post a pic of a similar auto part?
posted by artdrectr at 1:29 AM on April 8, 2013
When I have had to fix tiny plastic bits that undergo physical stress (like, say, the whammy bar yoke hidden inside a Guitar Hero guitar, or the spray lever cam inside a kitchen tap) I have used JB Cold Weld. It's ugly, but it is very strong after 24 hrs of setting, and I find it is perfect for fixing plastic bits that are often cheaply made and easily broken. One caveat is that you may have to cut away any runoff afterwards, if the piece has to be inserted into something else and you need clearance where the epoxy would otherwise dry and get in the way. This is easy to do with a Dremel-style tool with a cutting or sanding bit.
posted by Blazecock Pileon at 1:50 AM on April 8, 2013 [1 favorite]
posted by Blazecock Pileon at 1:50 AM on April 8, 2013 [1 favorite]
superglue is an adhesive, not a void filler.
it seems your specs require both adhesion and reinforcement. fiberglass and epoxy would be my uninformed choice, based on your limited description. it's strong, conforming, thin, temperature tolerant, relatively easy to use.
pix necessary for further recommendations.
posted by FauxScot at 3:09 AM on April 8, 2013
it seems your specs require both adhesion and reinforcement. fiberglass and epoxy would be my uninformed choice, based on your limited description. it's strong, conforming, thin, temperature tolerant, relatively easy to use.
pix necessary for further recommendations.
posted by FauxScot at 3:09 AM on April 8, 2013
Response by poster: The part is definitely not something which is going to come squirting out of a 3-d printer, I don't think. This ebay auction shows one of the repros, which I sheepishly admit looks better than the crude one I have on hand (so there's another out). The reproduction covers don't come pre-drilled with holes, there are about a dozen around the perimeter. It's about 10" wide by 18" long by 6" high.
I have considered JB cold weld--and may give it a shot, there's some on the bench. Like you say, it's a bit ugly to work with, but the flip-side is that it would be gap-filling, so repair bits would only need to be "close". The fact that I'm asking this rather than trying it says how much I "enjoy" working with it.
sugru: Looks interesting, not sure if it would be suitable. But interesting! And, sadly, I already know more about this than my local hardware store.
I'd like to fix this piece, of course, but I'm also interested in the repair as a more general learning experience, as broken plastic items are one of the hardest parts of restoring an old car or bike for me. Metal you can weld or machine or whatever, but plastic is always a puzzle. (And most of the time if reproductions are available, they aren't very good, or just don't fit.) Having a few techniques in my bag would make facing plastic challenges a lot more fun.
posted by maxwelton at 3:23 AM on April 8, 2013
I have considered JB cold weld--and may give it a shot, there's some on the bench. Like you say, it's a bit ugly to work with, but the flip-side is that it would be gap-filling, so repair bits would only need to be "close". The fact that I'm asking this rather than trying it says how much I "enjoy" working with it.
sugru: Looks interesting, not sure if it would be suitable. But interesting! And, sadly, I already know more about this than my local hardware store.
I'd like to fix this piece, of course, but I'm also interested in the repair as a more general learning experience, as broken plastic items are one of the hardest parts of restoring an old car or bike for me. Metal you can weld or machine or whatever, but plastic is always a puzzle. (And most of the time if reproductions are available, they aren't very good, or just don't fit.) Having a few techniques in my bag would make facing plastic challenges a lot more fun.
posted by maxwelton at 3:23 AM on April 8, 2013
Response by poster: To be clear, the cracks don't really need filling, as they press tightly closed...hence my idea of superglue or the proper equivalent. I feel fairly confident I can cut repair pieces that won't need much filling for the missing areas.
Fiberglass I have also considered, but I prefer working with epoxy, given the choice of the two.
posted by maxwelton at 3:30 AM on April 8, 2013
Fiberglass I have also considered, but I prefer working with epoxy, given the choice of the two.
posted by maxwelton at 3:30 AM on April 8, 2013
Just a word of warning: some plastics become brittle with age (and/or exposure to heat and light) - the cracking raises a little warning flag for me about this.
If you repair it, the part might just end up disintegrating further when you fix it and put it back in to place. Not very helpful, I'm sorry, but something to think about.
posted by firesine at 4:43 AM on April 8, 2013
If you repair it, the part might just end up disintegrating further when you fix it and put it back in to place. Not very helpful, I'm sorry, but something to think about.
posted by firesine at 4:43 AM on April 8, 2013
I think we need a picture to give you stronger recommendations.
My gut says your part might be celluloid rather than some more modern plastic. My gut also says you should consider Gorilla Glue rather than epoxy or superglue; epoxy is thick and needs space, which you don't have, and superglue is brittle and doesn't like flexible substrates. Testors Cement will happily bond celluloid BUT because of the way it works (melting) it is not great for fixing cracks, more for sticking bits to other bits -- testors repairs are often thin and brittle and just snap again.
posted by seanmpuckett at 5:29 AM on April 8, 2013
My gut says your part might be celluloid rather than some more modern plastic. My gut also says you should consider Gorilla Glue rather than epoxy or superglue; epoxy is thick and needs space, which you don't have, and superglue is brittle and doesn't like flexible substrates. Testors Cement will happily bond celluloid BUT because of the way it works (melting) it is not great for fixing cracks, more for sticking bits to other bits -- testors repairs are often thin and brittle and just snap again.
posted by seanmpuckett at 5:29 AM on April 8, 2013
Is there really no room for reinforcement, either inside or outside? I've had good luck with using very thin cloth and epoxy. Since you have a very small area to to do, you can go all out with the highest strength materials. You can get Kevlar cloth "tape" in 2" widths (made for seams on much larger projects), and high temp epoxy that is about 10x stronger than the hardware store stuff. I've used these two brands.
posted by 445supermag at 6:24 AM on April 8, 2013
posted by 445supermag at 6:24 AM on April 8, 2013
Not sure how much tolerance you have for this kind of thing, but visit The Compleat Sculptor and check out their mold making supplies. With a little practice, you can make molds and castings fairly quickly, and replicate things in a number of materials. Tints and fillers can be used and TCS has them, too. Not too cheap, but cheaper than a machinist. (Alternatively, you can hire a sculptor to duplicate it for you. We make molds a lot, though Jag parts are not as much fun as nekkid peeps. Tech is the same.)
O, and you can 3d print it. Check Shapeways.com Commercial printer of your designs. Cost reasonable, again, compared to a machinist.
(i am currently involved in a small project to make 3d copies of antique telescope parts in bronze, using 3d printing tech. )
posted by FauxScot at 6:54 AM on April 8, 2013 [2 favorites]
O, and you can 3d print it. Check Shapeways.com Commercial printer of your designs. Cost reasonable, again, compared to a machinist.
(i am currently involved in a small project to make 3d copies of antique telescope parts in bronze, using 3d printing tech. )
posted by FauxScot at 6:54 AM on April 8, 2013 [2 favorites]
3D printing can be used to make pretty much anything - don't discount it; the part you pictured from eBay auction is remarkably simple compared to the items I've seen our in-house shop guy pull from his printer. It's a curved shape, with some openings? Should be easy - because he can print moving parts.
If you simply want to stabilize the existing item, carefully covering it with Gorilla Tape may work (think Duck tape with Gorilla Glue adhesive on the sticky side); Sugru should be able to fill gaps if needed (I plugged a hole in my washer fluid reservoir with a gob of Sugru; it's silicon so it's flexible and heat-resistant once cured) but you really ought to check out your options for having a nice custom-printed replacement.
posted by caution live frogs at 11:23 AM on April 8, 2013
If you simply want to stabilize the existing item, carefully covering it with Gorilla Tape may work (think Duck tape with Gorilla Glue adhesive on the sticky side); Sugru should be able to fill gaps if needed (I plugged a hole in my washer fluid reservoir with a gob of Sugru; it's silicon so it's flexible and heat-resistant once cured) but you really ought to check out your options for having a nice custom-printed replacement.
posted by caution live frogs at 11:23 AM on April 8, 2013
A great balance between working with fiberglass and epoxy is just using the epoxy fiberglass resin.
It's slightly more difficult to work with because it's a bit more fluid than typical two part epoxies, but in my opinion it's worth it.
The big difference is that it's CLEAR, so once you've figured out how to do it, practicing on card board or something, you'll be able to sand it and polish it if you want and it'll look like the original piece, not a glued up mess.
Here's an example that I've brought over from repairing surfboards and boats to repairing cars and motorcycles.
Good luck and have fun!
posted by snsranch at 5:12 PM on April 8, 2013
It's slightly more difficult to work with because it's a bit more fluid than typical two part epoxies, but in my opinion it's worth it.
The big difference is that it's CLEAR, so once you've figured out how to do it, practicing on card board or something, you'll be able to sand it and polish it if you want and it'll look like the original piece, not a glued up mess.
Here's an example that I've brought over from repairing surfboards and boats to repairing cars and motorcycles.
Good luck and have fun!
posted by snsranch at 5:12 PM on April 8, 2013
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posted by lollusc at 1:16 AM on April 8, 2013 [1 favorite]