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I have a combination heatlamp-light-fan, somewhat like the one shown here. The surround (i.e., the big white piece of plastic shown in the linked photograph) is cracked between its outer edge and one of the holes into which a heat-lamp fits. Unfortunately there are no markings to indicate what kind of plastic has been used.

What sort of glue is likely to be suitable both for bonding and heat-resistance?

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I believe you're looking to repair the plastic trim piece. For that, I would suggest a model cement that would be available at your local big-box retailer (like Walmart, but, since you're in Aus - Bunnings is Aus only, right? - I would hope you don't have those there), or at a hobby shop.

The good model cements will actually slightly dissolve the plastic at the broken edges, then when the solvent evaporates (in a couple of seconds), the plastic will meld together into one solid piece. You're not actually gluing them together, you are, effectively, welding them together. You'll have a nice strong bond, and if done carefully, you won't even see the crack. If you use something like this, you may not even have to get the trim ring off the light, just squeeze the crack together tightly, apply the cement with a cheap, disposable, fine-point brush, and hold it for 5 seconds or so. This type of model cement is going to cost a bit more, but it will make a nearly invisible repair.

If you can't find that (or don't want to pop for the cost), a "regular" type of model cement (for example, Testors™ is the brand I'm most familiar with from my youth) will work as a glue. I'd suggest that you get the trim ring off the fixture and apply the glue from the back. Use it sparingly - it will take quite a bit less than you'd expect - applied to the crack from the hidden side because it can leave a bit of a mess.

Once you've got the repair made, you have, essentially, nothing but the original plastic trim ring, so there's really no need to worry about heat resistance. If the original plastic was sufficiently heat-resistant, the repaired plastic will be, too.

If, for some reason, either of these glues don't hold it, you'll have to track down the actual brand of your fan and look for docs online to see if they indicate exactly what kind of plastic it's made of so you can get a compatible adhesive. However, I really think that some model cement will do the job for you just fine.

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  • Solvent welding is the name for this method and it is the best method. I use Weld-on solvents but there are different types for different plastics giving modeling glue a try could be a first try that is inexpensive.
    – Ed Beal
    Jan 19 at 14:18
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Silicone is fairly heat resistant, epoxy is too.

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Following the answers that had been given by other users, I did some research on both silicone adhesives and epoxy adhesives. By chance, one of my search results was for a manufacturer and distributor of plastics near to where I live. I went to the distributor, explained the problem I had and asked for their suggestions and although I forgot to take the actual light cover with me, it didn't matter. The immediate answer I received was "Loctite 406, failing which, Loctite 454.". It turns out that both the Loctite adhesives are cyanoacrylates. Loctite 406 has exceptionally low viscosity, and a drop of it will flow into the thinnest of cracks without difficulty. In fact, the thinner the crack, the greater the bonding strength. Loctite 454 on the other hand, is of a gel consistency that enables overhead and vertical application. Since my light-trim was not (i.e., no longer) attached to the ceiling and I did not have to apply a glue to an overhead or vertical surface, I chose 406. The product data sheet indicated that it should withstand the temperatures near, but not actually on, the heat lamps without difficulty.

The repair went marvelously well. I also used the adhesive to repair 3 other cracked plastic objects including the trim on a ceiling-mounted fan and the lid of a trash can.

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  • CA is, basically, the same type of modeling glue I was referring to. I'm glad you got your situation resolved. Please be sure to check mark your answer so others know this has a resolution.
    – FreeMan
    Feb 15 at 16:14
  • It's worth noting that cyanoacrylate is not the same as as a solvent-welding adhesive. The cyanoacrylate does not harden because of the evaporation of a solvent; rather, the acrylate monomer rapidly polymerizes in the presence of water. The water vapour present in the air is sufficient to trigger the polymerization process. The final result is a layer of polymerized cyanoacrylate between the two bonded pieces of plastic. The heat-resistance of the acrylate will therefore be of importance in applications near high-temperature objects.
    – user02814
    Feb 16 at 15:12

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