Thinner gauged stainless steel sinks are prone to dents and punctures. To create a long-lasting repair without welding, you need to decrease the size of the puncture and use an FDA-approved stainless steel epoxy resin. FDA-approved epoxy does not contain toxins that will contaminate food or water.
Place the small piece of wood inside the sink, over the puncture and apply pressure to the wood with one hand.
Reach under the sink with the hammer and lightly tap the flared stainless steel around the puncture back toward the hole.
Remove the wood from inside the sink and lightly run one corner of it over the puncture to ensure the metal does not intrude into the sink. If the metal intrudes, tap the stainless steel out slightly with the hammer until the corner of the wood does not hang up on the metal.
Rough the punctured area on the underside of the sink with the 400-grit sandpaper to remove contaminates from the surface of the metal.
Wipe the sanded area with a clean dry rag to eliminate the metal dust from interfering with the epoxy.
Mix enough epoxy resin to cover an area at least twice the diameter of the puncture, per the manufacturer's instructions.
Apply the epoxy resin to the underside of the puncture. Work it forcefully against the surface of the stainless steel with your thumb to ensure proper adhesion and to eliminate air pockets from the epoxy bond.
Allow the epoxy to cure for the time specified by the epoxy manufacturer.
Lightly sand any epoxy that has entered the inside of the sink through the puncture with the 400-grit sandpaper to finish the repair.