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I have a fridge with a plastic shelf which first cracked, then finally split. Being short of cash and a replacement seemingly being not terribly easy to find, I thought I would see if it repairable.

To attempt repair of the complex crack, I have used PVC cement (intended for repairing plastic pipework, I think) liberally on the facing edges and in layers over the joint. This has provided sufficient strength for the shelf to support its own weight if held from either side.

Short of putting it back in the fridge with items on it (and potentially re-splitting the shelf!), will PVC cement be sufficient to return this to active shelf duty? I had thought of drilling and plating across the split; but I'm not sure how this plastic would take to drilling, especially relatively close to where it has split already.

shelf

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  • Hello, and welcome to Home Improvement. This is going to be hard to answer with just a picture. My personal guess is that it'll break again, but there's no knowing how long until that happens, or how much it will carry until then. Jun 23, 2018 at 20:31

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There is no glue job that involves just the edges of the plastic shelf that will hold up to any use. In fact it is rather amazing that you got it to bond with PVC pipe cement. Clearly the solvent in the pipe cement that you used was able to temporarily melt the plastic edges to the point of them bonding back together.

In order to get the fix to stand up to regular usage you are going to have to do some additional work. Find a type of glue that really takes to this type of plastic and use that to bond some metal cross bars to the bottom side of the shelf surface. Something like aluminum bar stock that is 1.5" (~38mm) wide by 0.25" (~6 to 7mm) thick that spans the maximal across the width of the shelf would be workable. I would suggest three such bars.

The ridges on the shelf, which appear to be on the bottom side, will require you to use a bonding agent that can fill in a gap. I would not recommend grinding off those ridges to accommodate the suggested cross bars. I would also not suggest trying to drill holes and using fasteners to secure the bars. This creates localized pressure points in the plastic that could cause it to crack from the drilled holes.

Experiment with silicon sealer type material to see of it bonds to that type of plastic. The plastic has to be clean, dry and oil free. If it does this would work well to bond the support bars to the bottom of the shelf. Silicon sealer material bonds very well to aluminum bar stock. If the silicon sealer is a non-starter with your plastic shelf then you could try one of the construction type adhesives. There are types that have solvents that allow them to bond well to certain types of plastic.

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  • Interesting that you mention solvent- a friend referred to it as solvent weld so I suspect you are right on that account! Helpfully, the ridges are not on the underside (they are grooves on the top), and I have silicone sealant to hand- just need to figure out where to acquire the aluminium bar stock and cut them to length :)
    – bertieb
    Jun 23, 2018 at 19:53
  • Depending upon where you live it may be harder or easier to get bar stock. Nothing would stop you from using steel or iron bars but they are much more likely to rust in the moist environs of a refrigerator. Do make sure to test the silicon before you commit to it. The test could be as simple of squirting a wad of it out onto the bottom back corner of the shelf. Let it fully setup and then try to see how hard it is to peel it off.
    – Michael Karas
    Jun 23, 2018 at 20:04
  • Here in the USA it is possible to get bar stock from local hardware stores. That is of course not the lowest cost way to buy it. You could also consider 3/8" x 3/8" angle stock as well. You can purchase the suggested 1.5"x0.25" aluminum stock from McMaster-Carr as part number 8975K518. A 6' chunk would set you back ~17USD plus shipping. mcmaster.com/#standard-aluminum-sheets/=1devzyk
    – Michael Karas
    Jun 23, 2018 at 20:19
  • That's really helpful information for comparison- I had no idea about the price of bar stock and could have believed anything within an order of magnitude! eBay has various lengths here but not terribly cheap; I'll check a couple of local hardware stores / metal suppliers and see what they have to offer.
    – bertieb
    Jun 23, 2018 at 21:06
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To attempt repair of the complex crack, I have used PVC cement (intended for repairing plastic pipework, I think) liberally on the facing edges and in layers over the joint. This has provided sufficient strength for the shelf to support its own weight if held from either side.

That's not going to work because that's not how PVC "gluing" works. It's not gluing at all. It's welding. It's not glue, it's solvent, it softens and melts the solid PVC into liquid PVC. The difference is, when the solvent evaporates, the two pieces of PVC are now one piece of PVC. That is because PVC is thermoplastic and capable of melting and re-hardening.

But if you try to use PVC solvent on anything else, you might melt it, or it might just react with it, or it might just do nothing.

To make a repair like this, I would do 2 things.

1. Glue it with something that'll work.

For that my go-to is FRP, or Fiber Reinforced Plastic. It's what they make boats and surfboards out of. Use "Fiberglass matt" combined with an epoxy you find easy to work with (here's the trick: Slower is better! 24 hour epoxy is not too slow. You don't want 30 minute stuff and then it's kicking while you're trying to work it. You only get one shot.)

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Lay the fiber so it goes 1-2" across the break.

Plenty of websites and videos go into length on epoxy lay-up, so I won't repeat all that. Except to add two things.

  • Heavily and obsessively "scuff-sand" the plastic surface so it is microscopically rough - the epoxy will need that to bind to, if you leave it smooth the fiberglass will just pop off, like a surfboard coming out of a mold.

  • Lay plastic sheet across the fiberglass before it dries, and smooth it down with your fingers. That will give you a nice smooth surface instead of the jaggy hand-scratcher you'll get if you don't. I use regular old plastic grocery bags, but really something the thickness of Ziploc freezer bags would be better. If the bag has printing on it, that will end up in the epoxy!

2. Physically reinforce it. Because it broke for a reason.

Flat plastic is not strong. All the strength in that tray came from the vertical ripples or grooves in it, particularly the tall ones going left to right. The top is in compression and the bottom in tension - look up how girders or trusses work, same deal. So those grooves are the key to the piece's strength.

And if you do your research on fiberglass boat building, you'll see such bending strength is added with "cores" - strips of wood or styrofoam that are wrapped in fiberglass-epoxy. The point is to make a fiberglass "pipe" - the strength is in the fiberglass, the core itself doesn't matter. That's why styrofoam is good enough.

I seem to recall they make foam tubes for sealing driveway cracks that are very inexpensive. Wrapping that with fiberglass and gluing it into the grooves would do wonders.

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  • I am slightly confused by the terminology here, at first it mentions a solvent that "melts" the plastic and then evaporates. But then it is mentioned that PVC is "thermoplastic", which implies that the solvent softens the plastic with heat (chemically generated?) instead of chemically dissolving/softening it. Is thermoplasticity relevant here? Jun 24 at 8:38
  • I think my terminology may have been confused in OP- whatever it was I assume it was for repairing pipes, but in a comment on sibling answer I refer to it as also being solvent weld... whatever it was it did enough to hold for a while! Didn't even think of the epoxy approach (we used it elsewhere to patch a lawnmower that had to have an access hole cut), that's a great suggestion
    – bertieb
    Jun 24 at 11:24
  • I'm intrigued by the "fibreglass pipe" concept too, intriguing!
    – bertieb
    Jun 24 at 11:25
  • @htmlcoderexe the properties coexist. Jun 25 at 1:18
  • @Harper-ReinstateMonica that doesn't seem to help much. Does this solvent both dissolve and heat the plastic? Jun 25 at 19:31

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