Plaster wall failure occurs for several reasons. Plaster is an extremely versatile product. The fact that is labor intensive and takes a long time to install has led to its replacement in most residential applications. One drawback to plaster is the fact that it is mixed in the field.
Human error and varying conditions can change the composition, and quality, of the plaster mix. Over time the coats of plaster can start to separate from one another. Or the entire plaster assemble may separated from the substrate.
Large areas of plaster can fall off or loosen up. When this happens, you are faced with a large plaster wall repair. Installing plaster for large areas is generally not practical. It can be done, but it is usually beyond the skill level of the average homeowner. See the articles on 'Drywall Patching' and 'Mixing Drywall and Plaster' for information on using drywall for a plaster wall failure. You can also see 'Spackling a Plaster Wall' for minor repairs.
For those that want to know what it takes, we will give you a quick run down. Plaster is normally installed in three coats. The scratch coat goes on first and is a fairly thin layer of base coat. The idea behind this coat is to get a good bond to the substrate. A wire tool is used to put scratches into the coat before it dries. The scratched provide 'keys' for the other coats to fill and bond to.