Terra cotta is a term used to describe dry, baked clay. It can be glazed or left natural. Natural terra cotta is not waterproof. This material has been used for centuries to make pots, figurines, sanitation pipes, and to make slates for roofing. Terra cotta pots come as small as 1/2-inch in diameter and up to 5 feet across. For ashtrays on the patio, you may want to use the glazed pots, which are waterproof. Terra cotta flower pots come with round trays to catch the runoff when plants are watered. These trays would make ashtrays with the perfect depth to add sand for extinguishing cigarettes.
Purchase enough terra cotta pots in the size you have decided to make your ashtrays. Remember to get the trays that come with the pots. The trays are usually free with the pots, but pots are sold without trays unless you ask for them, in some cases.
Turn one terra cotta pot upside down. Spread glue on the bottom of the pot.
Place a pot of the same diameter right side up on top of the upside down pot. Allow the glue to begin to dry before gluing the rim of the top pot.
Place the round tray on top of the glued rim and press firmly. Allow the glue to dry completely. Set the ashtray before filling the top with enough sand to come within 1 or 2 inches of the top. This will leave enough room to extinguish the butts.
Other designs can be created with the pots. All terra cotta pots are not round. You may wish to use square pots for your ashtrays. Make the ashtrays as tall as you like by adding two or more pots to the original two. Leave the first pot right side up; glue the tray to the rim; glue another pot to the inside of the tray and glue another tray to this pot. Fill both trays with sand or just the top tray.
Unglazed pots have not been kiln dried and are more easily broken when they fall onto a very hard surface, such as concrete.