Most homes built in the past 50 years have interiors made with drywall--large, thin sheets of paper-covered gypsum nailed directly to wall studs and ceiling joists. Drywall is inexpensive to buy and install and easy to repair.

Although durable, it is also easy to damage--doors bang into it, furniture scuffs and marks it, water damages it. Occasionally, drywall nails pop into view (most often in new homes because of settling or framing shrinkage), but drywall screws tend not to pop out. The areas between wood framing members are unsupported and therefore particularly vulnerable.

Before drywall, most homes had plaster interiors. Plaster work is still done in new construction, but it requires more skill and is more expensive, so today it is usually found in higher priced homes. Working with plaster requires practice--when mixed, it has a very brief “open” time when the material is liquid and pliable, but it sets quickly and becomes rock-hard in an instant. Plaster applied to wood lath is held in place by the “keys” that form when it squishes through the lath.