In spite of all their advantages, modern wood floor finishes will not last forever. Hardwood floors should be recoated when the original finish shows signs of wear, but before it has worn through the finish to the bare wood. Bare wood can be stained by dirt and grime, resulting in the need for re-sanding.
Many hardwood floors can be sanded and refinished at least once and as many as three times or more. The exact number depends upon the total thickness of the product or the thickness of the top layer of premium hardwood, as in an engineered product. While sanding and refinishing a floor may be costly and disruptive to the household, it is usually more economical than replacing the floor.
When your floor begins to look worn this is a sign that it may need sanding or refinishing. A simple test to tell what you need to do is to pour a tablespoon or two of water onto your floor. If the water beads, your floor is simply a little dirty or tarnished from wear and tear. The solution in this case is just some cleaning or stain removal. If over a period of a few minutes the water slowly soaks into your floor, your floor is partially worn and will need re-coating or refinishing soon. If the water soaks right in, it is time to re-coat or re-sand and refinish your flooring.