How do I temporarily fix this hole in sink? I need it to hold at least for a few days.
I hate "not answering the real question" but I also hate people wasting their time.
Instead of spending 20-30 dollars on 2 part epoxy and maybe making this waterproof AND chancing a small leak ruining the cabinet... You don't only have a chunk missing but you have a pretty good crack line running there too.
Please spend that time and energy to just swap out the sink. These are $50-70 new at big box and $10-30 at salvage materials places (I have put at least 10 decent sinks like this on the curb at houses over the past 5 years).
You have to replace it so why do steps X, Y, Z beforehand. Part of DIY is knowing how to save yourself time in the long run.
- Apply a bead of construction adhesive such as Loctite Power Grab to the exposed edges of the porcelain
- Put the broken porcelain back into place
- Duct tape it from the underside
- Cut a piece of lumber and put it under the broken piece so that it can apply pressure upwards
- A tensioned curtain rod would also do the trick if you can find one short enough to go under the sink
- Remove excess construction adhesive inside the sink
- Clean the sink with a damp sponge or cloth
- Construction adhesive generally does not like being exposed to water
- Inside the sink seal all the cracks with 100% silicone
- Let the silicone cure before using the sink
If you don't mind the silicone inside your sink then this could be a fairly permanary fix.
I would use some silicone adhesive caulking to glue the piece in place and then use some strong tape underneath to hold it in place. You might have to wedge a board underneath to hold the piece in as it dries if tape doesn't stick. Smear some of the silicone liberally over all the cracks inside the sink once the piece is in place. It won't be pretty or very strong, but it should make the sink usable for a while.
Tape the piece back firmly in place from below, possibly having a helper press it upward for you or wedging something against it. Then, use Loctite 420 or a similar extremely-low-viscosity CA glue product that's designed to wick into cracks and rapidly dry. You can remove excess with a razor blade and/or a paper towel soaked in acetone. It's good to have acetone ready in case you accidentally glue your hand to something with it too, because this stuff sets nearly instantly.
This will be a permanent fix if you want it to be.