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This horse stable has sliding doors with black bars. There are wooden rafters, along with concrete flooring.

How To Apply Polyurethane to a Wood Door

A beautiful wooden door with black handles is standing between tan, stoned walls. There are shrubs along the side of the entryway.


Wood doors have many benefits compared to their less expensive counterparts. For one, they are more attractive, even when you forego painting them since the wood itself is beautiful. They also provide better durability, energy efficiency and sound resistance than other materials, making them a great option for homeowners. 

Wood is a high-quality, natural material that isn’t necessarily cheap, so you will need to protect it. The best way to protect it and increase its longevity is to apply polyurethane products for wood doors.

Preparing the Wood

Before using a polyurethane finish, use a wood filler like ZAR® Patch Wood Filler to fill holes, repair cracks or gouges, fix broken corners and chips and other blemishes. 

To apply the wood filler to cracks and holes, follow these steps:

  1. Make sure the door is clean and free from dirt, oil and grease. You also want the area you are patching to be slightly damp for best results.

  2. Using a smooth-edged, non-metallic trowel or putty knife, apply some wood filler to the damaged area. You can also apply the filler directly from the tube.

  3. Pack the compound into the crack or hole and allow it to dry for one hour. Cracks and holes smaller than a quarter-inch deep typically require only one application while bigger cracks will need a second application.

  4. Once each layer dries, you need to sand it down to a smooth, flat finish and allow it to dry overnight before applying any oil-based products.

For open-grained woods, you need to mix the wood filler with water until it reaches a creamy consistency. Then, you can apply it to the wood, going against the grain to fill in the wood’s pores. After five to 10 minutes, you can scrape off the excess material, moving in the direction of the grain. After drying overnight, sand lightly and apply a polyurethane or stain.

How to Apply Polyurethane to a Wood Door: Brush-On Method

Someone is applying polyurethane with a brush, The brush has black bristles and a wooden handle.


The brush-on method of applying polyurethane to a wood door is the most common, and it is fairly easy. If you apply a stain, allow it to dry overnight before applying one of ZAR®‘s polyurethane finishes.

Make sure to remove all dust and debris from the surface of the wood with a vacuum. Certain products, like ZAR®‘s Poly Pro finish, require further preparation like removing finishes, sanding down the surface and cleaning with paint thinner, just depending on the type and condition of the wood.

For new wood, be sure to sand it down and vacuum any remaining dust

Start by stirring your polyurethane product. It is important when stirring to gently stir as not to cause air bubbles in the finish. However, there are certain gloss finishes paired with the polyurethane that do not need stirring. You do not need to stir the gloss finishes of the ZAR® Interior Oil Base, ZAR® Interior Oil Base High Solids and ZAR® Interior Oil Modified Urethane OMU polyurethanes. 

Products can be applied directly from the can, using a clean bristle brush or lambswool applicator. Be sure to let the excess product drip off.

Begin applying the polyurethane in the direction of the grain. Be sure to avoid overbrushing, as it can cause air bubbles to become trapped and may result in streaks. Apply the product in thin, even coats and allow it to dry thoroughly.

For instruction on how to apply polyurethane to a wood door, it is important to read the directions directly on the can, as specifics can vary. For example, with ZAR®‘s Poly Pro and High Solids products, you have to sand lightly between coats after they are dry and remove all dust particles. The directions will also tell you how many coats are recommended and how to clean up any messes or mistakes.

How to Apply Polyurethane to a Wood Door: Spray-On Method

This horse stable has sliding doors with black bars. There are wooden rafters, along with concrete flooring.


A newer method for applying polyurethane to wood doors is to use a spray-on polyurethane product. ZAR® Interior Oil Base Poly is a high-quality product that offers a spray-on option. 

To apply this product, the air and surface temperature both need to be between 65º F and 85º F. 

You will need to shake the satin and semi-gloss finishes vigorously, just like you would do with spray paint. However, do not shake gloss finish polyurethane.

Before applying the polyurethane, practice on a scrap piece of wood to ensure the correct technique. Apply the polyurethane in thin, even strokes. If any bubbles form, wipe them off using paint thinner or mineral spirits. 

Humidity can make drying times vary, so allow at least two hours between coats. If it still feels tacky after two hours, allow for extra drying time, then sand lightly. 

Wipe away sanding dust and reapply the spray, ensuring you apply a minimum of three coats, allowing the final coat to dry for a minimum of four to six hours.

The Best Polyurethane for a Wood Door

This entry has a gorgeous wooden door with a wreath on it. There’s a welcome mat, two plants, a plaid rug, a mailbox and two light fixtures incorporated in the design.


Wood doors are a beautiful addition to any home, especially as a front door. For superior protection, it’s best to use a high-quality polyurethane finish for wood doors. ZAR®’s oil-based polyurethanes provide quality protection for wood while being user-friendly.

While each product differs somewhat, the application methods are generally the same. The key to application is to prepare the door properly and take your time to ensure a smooth, even coat. 

ZAR® products make it easy to achieve a beautiful, clean finish. Find out where to purchase ZAR® polyurethane products for your wood door project.