Almost all of our walls and ceilings are plaster. Basically dried mud over lath (long strips of wood with spacing in between). I love the plaster walls, but it does have a tendency to crack as the house moves and settles.
The previous owners dealt with cracking plaster in several different ways throughout the house. When the Professor had to cut holes in the kitchen wall to run electrical wiring, we discovered that they simply placed drywall over the the original plaster:I also took the opportunity to look inside the wall. You can see older wiring, the outer wood siding, and the lack of any real insulation:You can't see it in the picture, but there is also a collection of broken plaster at the bottom.
While making holes in the wall was fun, I had to turn to Patch to fix them. I always get these images of bugs crawling out of the holes and that just creeps me out.I used steel wall patches. They are relatively inexpensive and they work great! They are actually stronger than the actual wall.You take a square of steel larger than the hole and butter the backside of it with joint compound or spackle. Then you press it over the hole and stick the fiber mesh over top of it. The fiber mesh is sticky on one side and adheres to the wall, holding the patch in place:Then you spackle over the whole patch and smooth it out. It's best to spackle a larger area than just the patch. It blends in with the wall better that way.Once it dries, sand the a area and paint over it. They work really well and are very easy to use. I recommend them to anyone with holey walls!