To fill small holes, use 100% SILICONE RUBBER (Clear). This is available in hardware stores in large caulking tubes or in a smaller “toothpaste” like tube. Squeeze the silicone into the hole or fine hairline crack of the pot and allow to dry. (about 6 hours)
To fill a large hole, you can use “BONDO” Body Filler – fiberglass resin. Bondo is available in automotive supply stores. It comes in a small tin which contains the filler and a hardener. Mix the filler and the hardener creams together on a disposable surface with a disposable implement. It has the consistency of toothpaste. Once mixed it will set up in about 5 minutes and then can be carved or shaped with a sharp tool and sandpaper.
(Please use with care. Use a vapor mask, eye protection and gloves. Follow the instructions on the can.)
EPOXY is the best glue for repairing broken pots. It is available in small quantities in “toothpaste” type tubes in hardware stores. EPOXY comes in 2 tubes: RESIN and HARDENER. Before mixing the resin and hardener make sure the two pieces to be glued line up and prepare a workspace where the pieces can be held firmly together for 5 minutes while the glue dries. Duct tape is a useful way to hold the pieces together while they dry. Mix the Resin and Hardener on a disposable tray with a disposable spatula or small implement. Apply to both sides of the crack. Press the two pieces firmly together so that the crack interlocks as closely as possible. Using duct tape and/or large rubber bands keep the pieces pressed together for at least 5 minutes. Excess glue can be chipped away later. Epoxy cures for 24 hours or so to achieve maximum strength but after 5 to 10 minutes the bond is quite secure.
Silicone can also be used to repair cracked pots. However, the results are a little less pretty. In both processes the surfaces must be totally dry and clean.
Mix 100% SILICONE RUBBER (Clear) and ODORLESS MINERAL SPIRITS (a kind of paint thinner) in the bottom of the same bowl or pot you intend to seal. A 50/50 mixture is about right. Dilute the silicone with the mineral spirits as you mix them together with an old or disposable brush until a smooth paint able consistency is achieved. You may have to add more or less MINERAL SPIRITS to get the consistency. Once the mixture is liquid enough, brush over the entire inside of the pots. It takes approximately 4 hours to dry to the touch but 1 day to cure completely.
Pots can also be sealed using basement sealing paint like “DRYLOK”. These opaque sealants can be painted directly onto ceramics or masonry.
CAUTION: “BONDO”, SILICONE RUBBER or MINERAL SPIRITS should always be used with adequate ventilation. Protect lungs, eyes and skin by using vapor masks, goggles and gloves especially when sealing large containers and always follow instructions on product labels.
A tile/ceramics bit is needed to drill most pottery. For porcelain, you'll need a diamond-tipped bit. The bit will wear out more quickly if it gets too hot, so we use water to quench our bits. Use a professional-grade drill, the cheap ones aren't built for heavy duty work. Always wear safety goggles when drilling, and be careful!