CGallery:
By "rock-lath" I presume you mean Gyproc Lath plaster walls.
There are different ways to repair plaster depending on how bad the damage is and how well you want to do the repair.
If it's a round hole in the wall, and you want a fast dirty, and cheap repair, you can simply drill two holes in the middle of a piece of wood that will fit through the hole. String some steel or copper wire through those holes, and paint the back sides of the wood with white wood glue. Slip the board into the hole and pull on the wires so as to pull the board against the back of the Gyproc lath. Now, slip a smaller board in between the wires and wrap them around each other until they're tight and the board is pressed against the back of the lath. Leave that over night and the board will be glued to the back of the lath pretty solid by morning.
Then, paint everything you want your base coat plaster to stick to with white wood glue and use some diluted white wood glue to mix up some base coat plaster and fill the void in the wall. Leave the base coat plaster about 1/8 inch shy of flush with the wall, and then fill that remaining 1/8 inch with drywall joint compound. Sand the repair down flush with the rest of the wall, prime and paint.
A much better way to do the repair would be to use a jig saw or drywall knife to cut the plaster horizontally to the closest wall studs. Then cut vertically up the sides of the studs to cut out a rectange of plaster. Now, use 3" drywall or decking screws to fasten spruce 2X2's to the sides of the adjacent studs. (Predrill your holes with a 1/8" X-tra long drill bit and countersink the holes to accomodate the trumpet heads of the drywall screws of flat heads of the decking screws.) Attach the 2X2's so that they're a little more than 1/2 inch inset into the wall, and then drywall screw your blueboard patch to the spruce 2X2's. Now apply drywall joint compound over the blueboard so it's more or less flush with the surrounding wall. Then, put fiberglas mesh drywall joint tape over the joint around the repair, spread more joint compound over the tape and blueboard patch, sand smooth prime and paint.
Alternatively, you can fasten your 2X2 nailers so they're flush with the adjacent studs, paint everything you want the base coat plaster to stick to with diluted white wood glue, sprea base coat plaster over the blueboard patch, apply your fiberglass mesh drywall joint tape around the patch, spread joint compound over the repair and sand smooth, prime and paint.
Or at least, that's the quick and dirty way and the much better way of doing a plaster wall repair.