I first tried the superglue-and-baking-soda trick back in Post #1997, where I made an expedient repair to a plastic-bodied wrist watch with a broken watch band lug.
FYI, the baking soda isn’t merely a physical filler, it interacts chemically with the superglue and cures the superglue in a completely different fashion from what would normally happen. The result is stronger than superglue alone, and has better adherence to whatever you’re trying to glue to (reference).
When my wife snapped the plastic frame of her eyeglasses last week, that method was the first thing that came to mind. Like the wristwatch lug, you have a tiny surface area of plastic to glue to, and yet the part has to take a lot of mechanical stress.
And, in fact, that same superglue-and-baking-soda method worked exceptionally well to hold her eyeglasses together until the replacement frames arrived.
As common sense suggests, first wash and dry both parts to clean the plastic surfaces. (Just dish soap and water).
Then, first super-glue the plastic parts back together, to get the alignment right. If the snap was clean, this should look good when re-assembled. But super glue, by itself, isn’t strong enough. Lot of leverage on this part.
And note that, for this next part, you need liquid superglue. Gel won’t properly “wet” the baking soda.
I then added a thin layer of baking soda and super glue all around the broken plastic. For a thin layer, just wet the plastic with superglue and quickly heap on baking soda. Give it a few seconds to harden. Brush off what remains loose. Use sandpaper to smooth the surface.
Alternatively, you can build the thicker part of the patch by first laying down a thin, shaped layer of baking soda (make a “wall” of masking tape around the edge to keep the powder from spilling over), then quickly wetting it with liquid superglue. That was shown in Post #1997, the broken watch lug post. When fully hardened, file it down and shape it with careful use of a common (flat bastard) metal file. Sandpaper to remove any rough bits.
The result is an unobtrusive and surprisingly sturdy repair. I didn’t try to match the frame color or otherwise make it blend in.
Better than a piece of tape, for sure.
It’s now been a week, and the replacement frames have arrived. I doubt that this repair is going to survive having the lenses pulled out of the old frames. But it was more than good enough to hold the broken frames together, until the new frames could get here.
I believe baking-soda-and-liquid-superglue is is now my go-to method for unavoidable repairs on rigid plastics.
