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How To Spray Polyurethane Finish In 5 Simple Steps

Mar. 2017

Polyurethane is one of the most beautiful finishes for wooden constructions. Its qualities and benefits go far beyond beauty as this finish is also known to be stain, spill and moisture resistance. It protects the underlying wood material from destruction as well as makes the construction more appealing.

However, applying polyurethane finish is not an easy task. Most professionals, as well as novices, have reported challenges when it comes to applying a smooth and clean polyurethane finish. Here is the good news, though, this article contains a comprehensive and easy to follow guide on how to spray polyurethane finish on wooden surfaces.

Important things to know

There are two types of polyurethanes with each type featuring different uses and application methods. To be able to apply any particular polyurethane varnish well, you will need to have all the necessary tools, materials and observe all safety precautions.

Choosing the type of polyurethane to use in your constructions will depend on various factors. The most important consideration is the type of project you are working on. Oil-based polyurethanes are much easier to use and are less susceptible to heat damages compared to water based polyurethanes. However, the oil-based option will require more time as it takes longer to dry, unlike the waterborne polyurethane which dries faster. The longer a varnish takes to dry the more vulnerable it gets to dust and dirt.

Tools and material

To be able to successfully and perfectly spray polyurethane varnish, there are essential tool sand materials that you will need to get ready before embarking on the actual project. These tools should be put in one place and close to you for easy and faster access. Here is what you’ll need for this project;

  • Polyurethanevarnish
  • Spray gun
  • Sandpaper
  • Tack cloth
  • Brush

How To

Finishing is as important as the initial step in any wooden construction. Therefore, you ought to be very careful from the start to the end of the process. Pay attention to every detail and observe all the necessary precautions.

Step 1: thorough sanding

For best results regarding varnish/finishing, proper sanding is essential; this is to ensure that the surface is smooth and free from grit for the finish to look good. To get rid of dust and achieve more continuous and perfect surface for varnishing, you need to sand the surface progressively.

You will start with a coarse sandpaper and then progress to a medium paper and lastly use finer sandpaper.

Ensure that the wood is free from any blemish after progressive sanding after that remove the dust. In this case, you can use a shop vacuum that has a soft brush add-on in removing the dirt then wipe it down using a lint-free piece of cloth which has been moisturized using the mineral spirits. Finally, to be fully certain that the wood surface is free from dust,wipe it using a tack cloth.

Step 2: seal the wood surface

What is required here is sealing the wood surface before applying the top coating. This seal should soak into the wood and fill the pores in the grain. It acts like a wood filler that levels the wood and not makes it blemished when applying the varnish. Once you have applied the sealer, allow it to dry overnight.

Step 3: Spray two extra coats of undiluted polyurethane

Once you have created the seal on the wood surface, wait for approximately 24 hours and then spray a new coat on the surface using a spray gun. When spraying, always spray in an even motion. When you start or stop in one position, the spray may build up in one spot causing an uneven finish.

Spray the varnish over the whole wood surface uniformly. It is, however, important not to use excessive spreads because there is a high chance of getting runs. Once the coat forms on the surface, let it dry for at least 24 hours before spraying the second layer.

Once 24 hours have lapsed, wipe off any dust and dirt and then spray on a second coat evenly too and let it dry fully for the same duration. The essence of the final coat is to ensure that the wood gets an ideal even surface that is free from any bumpy particles. Again, spray in excess the second coat as the aim is to get a spread that will provide a uniform surface.

Step 4: fix the bumps and gnats

After applying the second coat, remove any unwanted drips or dust speck that occurred during application of the previous coats and settled on the surface before drying. The moment the wood surface is thoroughly dry, perhaps after approximately 12 to 24 hours, you can use a razor blade to cut away any drips of dust specks.

In doing so, ensure that you only cut deep enough to allow it balance with surface and so it is necessary to take your ample time when doing this to get the right cut.

The next thing you need to do is to use a wet sandpaper to sand the surface to make it possible for you to get rid of blemishes or any dust specks. It is also recommended that you use adequate water in lubricating the sandpaper since it will prevent you from burning through the relatively subtle finish.

Sand the surface gently until you remove all the blemishes and dust bumps. When the surface finally feels smoother, take a wet cloth and use to wipe it and then dry it using a cloth that is dust-free.

Step 5: Spray the final coat

After a period of between 24 to 48 hours, you can now apply the final coat on the wood surface. If you are meticulous enough, you will be able to get an even and bump-free finish immediately this final coat dries up.

Use the same process as the one for step 3 but always remember that you will be required to polish the surface in any case you decide to wet-sand at this phase. Again if polishing is necessary, wait for a couple of days before applying it to allow the finish to dry fully.

After several days, clean the wood surface using a wet cotton cloth. Moisturize another piece of clean cotton cloth using a polishing agent and spray on the entire surface. Allow it to dry then fit the surface. The result will be a clean and shiny wood surface structure.

Keep these in mind when spraying polyurethane;

  • If possible, work outdoors this is because spraying is pretty fast and it is easy to mess up things when working indoors. However, if you must spray indoors, ensure that you cover anything around your work area like furniture and electronics.
  • Remember to spray in an even pace, starting and stopping at spots makes the spray to build up in one spot thereby creating an uneven coverage.
  • Also, overlap the spray half way past a previously sprayed section to achieve an even coverage on the surface.

In Summary

There are some aspects of home improvements that do not necessarily call for an expert since you can do it on your own as long as you have the appropriate tools and materials. You shouldn’t seek services of a professional to carry out something like how to spray polyurethane. You gain experience when you often do it on your own.

Additionally, you end up saving a considerable amount of money that you could otherwise use in paying someone else to do the task for you. Of importance is to ensure that you obtain the correct materials for this project and use this guide to help you in spraying your wooden surfaces from time to time. Nevertheless, never undermine safety measures when carrying out this particular task.

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