https://www.youtube.com/watch?v=L2T7W3TXgcE
Amazing korean vet repairs two snail's broken shells!
(english sub available)
Can #snail owners buy these materials? The glue looks like UV-hardening dental filler composite. I don't know what the desinfactant is, PHMB (often mislabelled as PAPB) maybe?
For small cracks, you can try covering exposed organs with a hydrocolloid plaster (ideally clean wipe the area with cold Catappa leaf tea). Skin rebuilds in days, shell in months. This saved my snail's life.