Can a plastic fridge shelf be definitively repaired?

Question

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.

Answer 1

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.

Answer 2

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.)

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.