1. Wash the mussel shells and remove remaining waste.
2. Cook the shells for 15 minutes.
3. Heat the shells for 1 hour on 200 degrees in the oven. This will make the shells more brittle .
4. Grind the shells into fine particles.
5. Sift shells with a 5mm sieve to control the maximum size of shell particles.
Put the ground shells in a bowl, and add the alginate and water. Mix until it forms a gell-like consistency.
Spoon the shell-alginate gell mixture into a mold and let dry into a hard, rigid brick. This can take 12-24 hours depending on humidity and temperature conditions.