Very good info site:
http://www.uky.edu/Agriculture/Entomology/entfacts/struct/ef603.htm<snip>
When carpenter ants are observed, don't spray them; instead, feed the ants small dabs of diluted honey placed onto the back (nonsticky side) of pieces of masking tape. The best time to do this is late at night since this is when carpenter ants are most active. After the ants have fed on the honey, follow them on their journey back to their nest. Be patient-- eventually the ants will disappear behind a baseboard, cabinet, or into some other concealed location such as the hollow space (void) within a wall, door casing, or porch column.
Treat wall voids and other hidden spaces where ants are entering by carefully drilling a series of small (1/8 inch) holes and puffing boric acid (available at most hardware stores) into the suspected nest areas. The boric acid powder will disperse in the hidden void and contact and kill the ants. If you suspect the nest is in a wall, drill and treat at least 3-6 feet on either side of where ants are entering so as to maximize the chances of contacting the nest. Carpenter ants prefer to travel along wires, pipes and edges. If you suspect the nest location is in a wall, also treat behind pipe collars and behind --not in-- the junction box for electrical switch plates/receptacles. NEVER SPRAY LIQUIDS OR INSERT METAL-TIPPED DEVICES AROUND ELECTRICAL OUTLETS!).
As noted earlier, carpenter ants seen in the home may actually be nesting outdoors, foraging indoors for food and/or moisture. Consequently, the homeowner may end up following the ants they have baited with honey out of the house and into the yard, possibly to a nest located in a stump, or under a log or railroad tie. Once the outdoor nest is discovered, treatment can be performed by spraying or drenching the nest with an insecticide such as carbaryl (Sevin), diazinon, or chlorpyrifos (Dursban). If outdoor nests are suspected, the homeowner should also inspect around the foundation of the building at night with a flashlight, especially around doors, weep holes and openings such as where utility pipes and wires enter the structure. The baiting approach using honey can also be used to trace carpenter ants which are foraging outdoors back to their nest.