Repairing an antique farmhouse sink requires disconnecting the sink from the drain and water supply, removing all of the sink's metal parts, cleaning the sink thoroughly, scuffing its surface with sandpaper and finally applying a restoration epoxy. Restoration epoxies are available at nearly all home centers and hardware stores.
Disconnecting the sink from its water supply and drain are essential if the sink is still attached to these fixtures. If the sink is not disconnected from its water supply, water can leak out during the repair process, potentially disrupting the epoxy's curing process. Failing to disconnect the drain allows epoxy to enter it; if enough epoxy enters the drain to cause a blockage, the pipe is ruined and requires replacement.
Felt paint rollers, paint brushes, trowels and even airless epoxy sprayers are all appropriate tools for applying the epoxy to the surface. Mixing the two elements of the restoration epoxy only immediately before applying the material to the prepared sink is essential. While an epoxy takes hours to fully dry, the product starts curing the moment its two elements come into contact. A partially set epoxy is difficult to apply at best, while in the worst case, the epoxy may cure so fully that applying it is impossible.