If you want to have a long lasting protection for your wood surface and make it look beautiful in a natural way, then covering it with a polyurethane varnish is an excellent choice.
Polyurethane is among the most durable and toughest clear coatings. Spraying polyurethane can be one of the messiest jobs to accomplish. However, if done the right way, it can bring out the inherent grain and beauty of the wood and protect it for a long time.
You can get a smooth and blemish free finish with polyurethane if you follow the essential steps listed in this guide. Tips presented in this article will help you understand the intricacies of spraying polyurethane varnish and teach you how to do it like a professional.
What is oil based Polyurethane varnish?
Polyurethane is an ultra-resistant varnish formulated so that its microscopic chains of resin molecules will bond tightly with one another as it dries. As a result, polyurethane coat adheres to the surface it is sprayed on and gives a finish that is much more resistant to water, solvents, heat, abrasion, and impacts than any other traditional varnishes.
Oil based polyurethane varnish gives the wood a warm and amber tone. It forms a hard and tough film in few coats. Oil based varnish mixture provides attributes of both ingredients, easier application of oil and protective qualities of varnish. It generally dries slower than other varnishes which mean you have to wait longer between coats.
Step by step spraying polyurethane guide
Preparation work: Tool, Material, and Environment
Before you start spraying job, it’s critical to do some preparation work. It involves setting up the tool, material, surface, and environment.
First of all, your workspace must have enough light and proper ventilation. A dust-free space is essential to achieve a perfect and flawless finish.
Polyurethane has a strong smell and is dangerous to breathe, so work outdoors if possible. If you are working indoors, select an area that is well ventilated and wear a respirator to protect yourself. Work with open windows. The workspace shouldn’t be too cold or damp as it may affect the dry times of coats. During the drying process, fumes have emitted that need to be dispersed. Having an exhaust fan facing out is a good thing to remove vapors.
You need an HVLP sprayer for application. Our recommendation on that is DeVilbiss 802342 StartingLine HVLP Gravity Spray Gun Kit. This sprayer is fast and creates a fine mist of solvent that settles on a surface to give a smooth finish. With this sprayer, it’s much easier to manage the application as you can change air speed, volume, and pressure. It gives you a charming pattern when you spray against the wood.
And more, you need a portable compressor to make air. Set the pressure at very low at around 10-15 psi and then change accordingly to your desired pattern and thickness. While preparing the solution, you can use 2 parts of polyurethane to 1 part of mineral spirit for wider coverage without being too thick. A good mix will prevent overspray and avoid dripping.
You can see that step by this video (doing by DarbinNotes)
Prepare the Wood
Any varnish demands a smooth surface to sit properly and look good. Make sure the wood surface is ready to receive a coat by first sanding with medium grit sandpaper in the direction of the grain. Then use a progressively finer grit sandpaper.
For small wood projects, sanding by hand is best. Cut the sheet of sand paper and fold it beneath your fingers. For large, flat surfaces, an electric orbital or palm sander can be used, or you can wrap the sandpaper around a scrap piece of wood for flat surfaces.
After done with sanding, carefully examine the surface. Look closely for any scratches left by coarse-grit sandpaper. Once the wood is blemish free, remove the dust. After sanding, wood is ready for a clear protective finish to be applied.
Apply a wood stain
If you plan to stain the wood surface, this is the stage you have to apply it. Choosing a stain is a matter of personal preference. There are a variety of stain colors that feature traditional wood tones and coordinates with your décor. No matter what type of stain you choose, make sure the surface is dry, clean and free of dust. If you don’t plan to stain the wood, you can skip this step and proceed directly to next.
Build polyurethane finish coating: Tips and Advice
Start and stop spraying at far edge
Start spraying the varnish in an even manner, move across the project at an even pace and cover the entire surfaces. Be ready to apply a coat in a continuous manner. Because if you start and stop spraying, it hard to get an even coverage. Spattering is the problem that occurs when you apply the polyurethane improperly, and it can blemish the surface. To avoid this, start spraying before you reach the edge of the wood and stop when you have gone past the far edge. This way ensures spattering free coverage across the entire surface.
Do not spray in an arc
It’s quite natural to spray in an arc. This spraying type gives varnish buildup in the center and light on the edges. To avoid this uneven spray coverage, move your full arm over the surface of the wood at the same angle. Do not just swing the sprayer.
Keep parallel spraying
Keep the spray tip parallel to the surface at all times. Move the sprayer at a steady pace while keeping it at an equal distance from the surface. The goal is just to spray enough polyurethane to wet the surface. Apply several thin coats instead of few thick coats which create runs. The surface may look blotchy after the initial coat but will lead to more uniform finish in the end.
Overlap the spray about halfway on to the previously sprayed surface in order to achieve a uniform finish in the end. Overlapping ensures the same finish everywhere.
Before applying the final coating, wet sand the surface with fine grit sandpaper. It will give you a smooth surface free of bumps. Wait at least 48 hours before polishing the surface with rubbing compound. Apply the polish onto the surface using a circular motion. After rubbing, let the surface dry and buff with a dry cloth. Here, you have a great looking finish.