Safe Handling

• Once it's dry, polyurethane is perfectly safe for kitchen counters where you'll be preparing food. In liquid form, however, polyurethane is extremely toxic and contains carcinogens. The fumes may cause irritation of the eyes, nose and throat. Skin contact may also cause irritation. Prolonged exposure may cause long-term respiratory issues. Before you even open the can, make sure you are wearing protective goggles, gloves and face mask. Always work in a well-ventilated area.
  
  

Benefits

• As a wood sealer, polyurethane is one of the most durable and impermeable options. It is commonly used in ship building to seal wood and fiberglass, protecting it from harsh weather conditions and constant contact with seawater. This means that sealing your kitchen countertop with polyurethane will help protect it from spills and minor damage caused by dropped utensils and cookware. Polyurethane also stands up to alcohol better than most types of wood sealers, though quick cleaning is still recommended.
  
  

Sanding and Staining

• Before you apply polyurethane, you must at least sand the wood properly. This is especially important if the countertop has already been stained and sealed with some other wood sealer, such as varnish or lacquer. Staining is optional, but you have to sand to ensure the wood will properly bond with the polyurethane. As with most woodworking projects, start with medium grade sandpaper to strip the surface, and finish with fine grade sandpaper to make the wood smooth.
  
  

Proper Application

• Once the counter is sanded down and stained, if you opted to stain the wood, you're ready to seal the wood. When mixing polyurethane, stir gently -- never shake the can. Mixing too vigorously will cause air bubbles that will get trapped in the finish. To avoid leaving marks from a paintbrush in your finish, use a foam or lamb's wool applicator to spread the polyurethane over the wood. Because kitchen counters typically experience heavy use, apply four or five coats of polyurethane to create a thick seal. For best results, sand the polyurethane between each coat with very fine grade sandpaper.