Polyurethane is a finish coating that can make any wooden surface more durable and beautiful. It is a protectant and sealer which keeps moisture from damaging the wood.
It is also a finish coat that brings an immaculate shine and magnifies the beauty of everything from flooring to furniture.
Polyurethane is a varnish that is specially formulated so that the resin molecules in it will bond together as it dries. When this bonding happens it causes the varnish to create a shield of protection around the wood it is applied to.
When you finish an item with polyurethane it is protected against:
- Water and humidity
- Abrasions and scratches
- Solvents and other spills
- Day to day life
Before you can begin to spray/brush polyurethane you need to decide whether to use a water based poly or an oil based poly.
Water Based Polyurethane VS Oil-Based Polyurethane
The main considerations between the water or oil-based items will be the durability factor. Oil-based is more durable and will provide a longer lasting finish, but water-based polyurethane is clearer and suitable for all wood types, and colors.
Water-Based Polyurethane Is Perfect If:
- You want the wood you are finishing to retain its natural light coloration.
- You want each coat of polyurethane to dry quicker. You can usually reapply another layer after waiting for two hours.
- You want a polyurethane that has a lower number of volatile organic compounds
- You do not mind applying more coats of the varnish to achieve the finish you desire. Commonly you will need to apply at least three coats of this type of poly to create a surface appearance that you are trying to achieve.
- You want to be able to clean up using simple water and a mild soap
This type of polyurethane is mixed with acrylic resins. The acrylic resins cause the liquid to appear cloudy or milky in the paint can. It will retain the milky appearance as you apply it to the wood, but when it dries it will be crystal clear.
This type of polyurethane is not as durable and protecting as the oil based varieties are.
It is available in gloss, semi-gloss, and a satin finish.
Oil-Based Polyurethane Should Be Used If:
- You want the hardest and most durable finish
- You like the added richness and warmth it brings to the wooden surfaces
- You want to complete the polyurethane application in fewer coats
- The item you are coating will be subjected to high levels of abrasion. Chair-rails, wainscot, and flooring are prime examples of high abrasion items.
- You do not mind waiting a little longer between each application. It will take between four and six hours for this type of poly to be dry enough that you can apply another coat.
- You do not mind the higher volatile organic compounds
- You do not mind using mineral spirits to help you clean up when you are finished applying the poly
This is the most durable polyurethane and it provides the maximum amount of protection to the wood.
You can get this poly in a gloss, satin and asemi-gloss finish.
You Can Also Get A Water-Based Oil-Modified Polyurethane
This type of poly is perfect if:
- You want the fast drying of the water based poly. You can usually apply the next coat after 2 hours.
- You want the deep amber and rich tones that the oil based poly can bring to wood
- You want to be able to easily clean up with only mild soap and water
- You want the lower amounts of volatile organic compounds
- You want a poly that is compatible with all manners and types of wood
With this type of poly you get the durability and coloration that you like from the oil based products. You also get the fast drying times and the easy clean up that you like in the water based products.
This poly is available in gloss, semi-gloss and satin finishes.
This type of poly will require at least three coats before it achieves the finish you desire.
Can You Spray Polyurethane – How To Apply
Once you have determined the type of polyurethane that you desire, you need to decide how you wish to apply this product. You can apply it using a paint brush or you can apply it using a paint spraying gun.
Using Paint Brush
If you apply poly using a paint brush you will quickly discover that you can see the small delicate lines that the bristles of your brush make.
After you apply each coat of poly you will have to sand it lightly to remove the brush strokes, dust it completely, and then apply another layer of the product.
You have to use a high-quality brush that has the perfect angle. You also have to develop a feather light touch so that your brush strokes are less noticeable with each poly application.
Many people have discovered that a paint sprayer will allow you to apply layers of polyurethane without brush strokes. These sprayers also allow you to apply lighter coatings of the substance so each layer dries quicker.
How To Spray Polyurethane Paint?
Follow these easy steps and you are sure to get a beautiful finish from your sprayed on polyurethane.
- Prepare the Item.
- You will need to sand the item so that it has a smooth and flawless finish.
- Then you will fill any holes or cracks with a wood filler.
- Stain the wood the color that you desire
- Allow the object to dry completely before you begin to apply the polyurethane
- Create a dust free environment to work in.
The slightest bit of dust in wet polyurethane can hinder the finish. You can apply the poly in your garage, workshop, or you can even pitch a tent and apply the poly inside the tent where dust particles cannot be blown onto your finish.
Set Up Your Sprayer
You will want to read the manufacturer’s instructions and follow them closely.
- Choose the right tip
- Adjust the volume control so you can apply a perfect layer. If you apply too much poly at once you will get runs and drips.
- The experts say that you should spray the poly on, and on each third stroke you should overlap the poly slightly. This helps you to create even coverage.
- Pour the poly in the sprayer
- Thin the poly if the manufacturer suggestions recommend that you do so
- Spray a test sheet of cardboard to determine if the poly is too thick, too thin, or if your technique is going to work properly for you
- Apply the poly
- Allow the poly to dry completely
- Sand the poly and dust all of the particles off of the piece
- Repeat the poly applications until the item looks and feels exactly like you want it to.
- Clean your spray paint gun immediately using mineral spirits if you were using an oil-based polyurethane
Polyurethane Tips From The Pros
- Always strip the old finish if any lacquer or wax are present. You can test for lacquer or wax by dropping water on the item. If the water creates a white spot then there is lacquer or wax present.
- Stir the can of poly completely. The stirring will combine the ingredients so you will get the best color sheen and the most UV protection from your poly.
- Apply poly in thin layers. Thin layers dry more quickly and you get fewer drips and wrinkles in thin layers.
- Always sand between poly coats. You want to use a 220 grit sand paper as it will smooth away the slightest of imperfections.
- Never hurry when you are applying poly.
- Use a dry micro-fiber cloth and dust the surface after you sand. You can also use a cloth dampened with mineral spirits to dust after you sand an oil-based poly. You can use a water dampened cloth to dust after you sand a water-based poly. The most minute dust particle can cause a blemish in your finish. So carefully dust away all residue left by the sanding after each application.
- Never shake your poly container. The shaking motion will create air bubbles in the poly. The air bubbles will create a pitted surface that feels rough to the touch.
- Never thin the first coat of poly. There is a myth that thinning the first coat will cause the poly to adhere more completely. This is a myth and all that the extra thinning does is make you have to apply another coat.
- Never use a tack cloth to dust the poly surface. These cloths contain chemicals that react with the poly. The reaction stops the poly from adhering as well.
- NEVER apply wax and then try to apply more poly. Wax will interfere with poly.
- Never smooth over a coat of poly using steel wool. Steel wool will leave tiny bits of steel in the poly finish and you will not notice them until later when they start to rust and corrode. Always use sandpaper between coats.
Safety Precautions To Take When Applying Polyurethane
- Do not smoke near this substance as it’s flammable. Do not store this substance next to gas water heaters or sources of open flames.
- Wear a face mask that will help protect you from breathing in the strong fumes. The fumes produced by polyurethane can burn your throat and cause permanent damage.
- Wear goggles to protect your eyes while applying polyurethane. Slight splashes of polyurethane into your eyes can have devastating results.
- Use in a well-ventilated area. The fumes from the polyurethane can build up and become hazardous if there is no proper ventilation.
Frequently Asked Questions
Is Spray Polyurethane Better Than Brush?
When you use the spray polyurethane you do not have to worry about brush strokes or fibers from the brush being in the finish.
You do have to worry about applying the polyurethane so that it is in thin coats that dry quickly, otherwise you might see obvious start and stop lines.
How Do You Apply Polyurethane To Spray On Wood?
Fill your paint sprayer with your polyurethane and spray a fine mist onto the wooden surface. You must make sure that the wood is lying flat and level when you begin to paint.
Also make sure that you spray in continuous movements to minimise drips or blobs from forming.
What Type Of Spray Gun Is Best For Polyurethane?
An HVLP gun is the best gun for this procedure. The LVLP gun is basically a gun designed for commercial operations and does not do well with this type of spray paint application process.
Be sure to clean your gun thoroughly with mineral spirits after you complete your polyurethane application. Do not let the substance dry on the interior of the gun.
How Many Coats Of Water Based Polyurethane Should I Use?
It is recommended that you apply at least three coats of this substance. With each subsequent coat the shine will be intensified and the protection will be increased.
If you are using the polyurethane on a table top or a cabinet top then you might want to apply as many as ten coats.
Polyurethane is the icing on the cake, so to speak. It creates the durable and beautiful finish that makes your wood projects look their best.
The application process for polyurethane is time consuming, but the time is well spent and the results will make you glad that you took your time and used this product.