• Molding is the wood trim that goes around windows, doors, along the floor, around the ceiling and anywhere else you need a border between two different areas. There are many kinds of molding, but most have similar installation procedures, starting with the necessity of mitering the corners. Choose your trim based on the decor of the room, taking into account whether it's plain, ornate or modern.
  
  

Preparation Issues

• Trim generally comes unfinished. If you install it on the walls that way, it's much more difficult to finish it than if you finish the trim ahead of time. It's important to sand the trim no matter what kind of finish you're putting on it, to take off any grime and surface dirt before you start. If you are painting the trim, apply a layer of primer, let it dry, and apply the first layer of paint. You can paint the rest after it's on the wall. If you are staining the trim, stain it before you put it on the wall and apply one layer of polyurethane. You can apply another layer after it's installed.
  
  

Measuring and Cutting

• In most cases you will use a full piece of trim for each span of the wall, door or window. Rather than measure the length of the span and try to cut both ends to make it exact, it's better to cut the miter on one end while leaving extra room on the other. That way, you only have to get the second miter exact. The miter cuts will generally be 45 degrees, so that they make a 90-degree corner when put together. For regular corners, use an angle finder to measure the angle, then divide it in half and cut each miter at that reading.
  
  

Installation

• There are generally two ways to install the trim molding: by hand, or with the use of a trim nail gun. Either way, you should put nails along both edges of the trim, every 10 to 12 inches. If you nail it in by hand, pre-drill pilot holes before you hammer in the finish nails, so that they don't split the wood. Then use a nail set to sink the heads.