You're funny, Tessa! I understand what your concern is, but I think you misunderstand terra cotta pot dynamics a bit.
If you like terra cotta pots because they breathe and thereby help curb root rot, then by sealing the outside of the pot, you defeat that purpose. An unsealed pot will allow moisture to evaporate through its pores. With a sealed pot, the moisture is absorbed by the pot until it reaches the sealed outer wall and then the terra cotta becomes saturated because it has no place to go.
Unsealed terra cotta pots do dry out sooner and do require more frequent watering (by a day or two, typically). But that is a good thing. Ideally, a plant
will dry out every 3 to 7 days. If it goes longer than a week (Cacti and other succulents
excluded), then you do start to run an increased risk for root rot.
Unsealed terra cotta does not "steal" moisture from the roots. It does absorb the excess water and allow it to evaporate.
As long as you have a waterproof saucer or plate under the pot, then sealing the pot should make no difference. The excess water will run through the drainage hole in either case. BTW, there are plastic, terra cotta-colored saucers that work very well with terra cotta pots and they are waterproof.
If you still want to seal your pots because you don't want to water them so often, then consider potting them directly into a plastic pot and then putting the plastic pot inside the terra cotta pot. This gives you the terra cotta look without the terra cotta evaporation.
I hope I have answered your question, although I, too, am now guilty of being long-winded! Let me know if you need further clarification.