what about grout sealant. its used on kitchen tiles. maybe theres a food grade grout sealer.

There is a sealant for wooden salad bowls, but I'm not sure of the name, maybe try a google for something along the lines of food safe sealants.

JoJo

>>> But I don't want to use anything that is a chemical, like a paint or something like that. I know there has to be a natural water proofer out there that makes sense. I just don't know what it might be.

That is really limiting your options. There are plenty of natural based types of water-proofers/sealers that can be used, but the problem is duration. All the options I'm aware of will wear off when used as a planter and submitted to frequent watering. Some wear much faster than others: non-drying oils, vaseline, etc won't last long vs. sealing with waxes will be longer but not much more than a season. Shellac is an amazing product is considered food safe (though don't ask where it came from). Once you open the typical can of shellac sealer, you will immediately think "chemical" however and it's mixed with an alcohol base to form a varnish. That will also wear when used to seal internally.

You could try gluing bubblewrap or thick (8mil) plastic to the interior, but that isn't completely waterproof. But if you're even willing to use glue, that is a chemical too and you could even superglue the entire interior.

I know quite a bit about sealers from woodworking, but understand I don't know much about TC other than the latest status-quo is using concerete/masonry sealers (which is what you want to avoid). What is the reason you want to avoid using "chemicals like a paint"? There is the Garden & Flower Crafts forum.

I think you may have to just move on.

What about using them as cache pots? There are lots of "pot liners" available (florist supplies may be a good place to look).