Woodworker’s Spray Finishing Tips



I’ve been using my Earlex HV6900 for about a year, and sprayed with other methods before that. I’ve sprayed paints, lacquers, polyurethanes, and shellac. Now that I’ll be spraying a lot more, I thought I’d write down some tips to share with you and as reminders to myself. I’d love to read your tips too, so please add them in the comments section.

Preparation is key

You need to prepare the piece for finish, prepare the space for finishing, prepare the finish, and prepare yourself.

Garbage in the shop, garbage in the finish. If you are applying finish to a piece that is not well sanded, or not wiped clean, don’t expect good results. If you are applying finish in a messy shop, expect dust nibs in your finish or droplets of finish to settle out of the air and onto your tools. On the day before finishing sand the piece well, clean up your shop, clear a space for finishing, setup your Portable Spray Booth, and let any dust settle out of the air. If you have an air cleaner, run it. But turn it off a few hours before finishing so that you don’t have the circular airflow in the shop stirring up dust and creating a secondary airflow that competes with your ventilation.

Check your equipment. Make sure that you have chosen the right needle for your finish and your gun is clean and working well. Run some denatured alcohol through the gun to make sure everything operates as expected, and re-familiarize yourself with the controls. If your gun isn’t clean, clean it thoroughly.

Prepare the finish. The sprayer manual will tell you how to measure the viscosity of the finish, and the label on the finish will tell you if you can thin the product, and which thinners to use. Test the viscosity, add any necessary thinner, stir well, and filter the finish.

Always, always have great ventilation. This is true for all finishes, and especially true for non-water-based finishes. You do not want to create large flammable cloud in your shop if you have open flame, a furnace, a water heater, or anything else that could create a spark. If you are spraying in your garage, shut off your furnace so that you don’t create secondary air currents or draw the fumes into your home. My Portable Spray Booth is a ‘wind at my back setup’ drawing the airflow from the space behind me, past the piece, and outside.

Always, always wear a mask. Even if you are obeying the ventilation rule you should wear a mask rated for filtering chemicals. All finishes contain things you don’t want in your lungs even in small amounts. Paper masks won’t help you here, get a real mask like a 3M 7500 with Organic Vapor Cartridges. Eye protection is also a very good idea.

Light the piece well. Especially if you’re spraying a clear finish it can be hard to see how well you’re progressing. A raking light is a great idea, cast a light on your piece at an angle and you’ll be surprised at what you see.

Plan your attack. Think about how you’ll spray the piece, and if you’ll need anything to help you spray. You may need Painter’s Pyramids, a finishing turntable, or a ladder to get the top. You’ll need a clear floor so you don’t trip. You’ll need to know if you’ll be spraying the underside, inside, or back of the piece, and in which order you’ll spray. You may want to think about managing the air hose so that it doesn’t get in the way or rub on the piece. Plan where you will place your turbine (if you have one).

In general, for spraying cabinets I spray the underside to seal the wood, set the case up on Painter’s Pyramids, spray the back, then turn the piece so that I’m looking into the case. I then spray the inside of the case from the furthest inside the case and work my way out. Think to yourself “inside out, top to bottom.” At this point, if I touch the top or the sides it’s ok – there is no finish on them. I then spray the top starting at the the point furthest away and working towards myself. If the hose touches the sides it’s ok – there is no finish on them. The front and sides get sprayed last, and then I back away and let the finish dry.

Don’t Spray A Thing

If you’ve done everything above, you might think you’re ready to spray. Don’t you dare. Get yourself a test piece of wood and follow these steps first.

Spray the minimal amount with the smallest needle. Tighten the fluid adjusting screw all the way. You won’t be able to pull the trigger, and nothing will come out of the gun. Begin to slowly back out the fluid adjusting screw until you get a fine atomized mist. If you have to open this all the way the needle is too small or the finish is too thick. If a lot of material comes out when the knob is barely open, your needle is too big. I’d also say that the material is too thin, but you can’t really un-thin your finish.

Test fire your gun. Using your test piece, which should be the same material as the final piece, test the spray and examine the results. Determine how fast you should move the atomized finish across the piece, how far away from the piece you should hold the gun, and how much overlap you need in your spray pattern. If you’re not happy check the sprayer manual and the finishing label. Most have a troubleshooting section to remedy common problems. In my Earlex manual, that’s page six. If the manual doesn’t answer your question, contact the spray gun manufacturer or the finish manufacturer. I’ve been able to get quick informative email replies from Bullseye, General Finishes, and Earlex.

Pass the test. If you don’t pass the test, don’t apply finish to your piece. It’s that simple. You’ve worked very hard and you do not want to make a mistake at this point. Do not move on until your gun is spraying a nice coat of finish consistently. Besides, sanding sucks.

Start On A Good Note with a Good Coat, and Repeat

Hooray! Hooray! It’s time to spray!

You Are a Robot, Not a Meat Popsicle. You are not a human when you spray, you are a robot. Do not swing your arm at the elbow or shoulder, instead you need to articulate your entire arm or move your entire body so that the gun is always the same distance from the material, perpendicular to the piece, and moving at a consistent rate. If you swing your arm or bend your wrist the gun doesn’t travel in a straight line across the piece, it travels along an arc. This changes the angle at which the finish is applied and therefore changes how much finish adheres to the wood because the angle at which you apply is one factor in how much finish bounces off the wood. Moving the gun along an arc also changes the distance at which you apply the finish and therefore how big the droplets are, how wet the droplets are, and how fast the droplets are moving when they hit the wood. If your piece is wet in the center and dry on the edges you know you’re not a robot.

Spray off before you spray on, and spray off again. Start spraying with the gun pointed off the piece, move the atomized finish across the piece in a straight line at a consistent rate and off the other side, and then release the trigger. Don’t point the gun at the piece when you pull or release the trigger. The atomization is a bit inconsistent at these points (high pressure during pull, low pressure at release), so only use the consistently atomized finish that is released between the trigger pull and trigger release.

The first coat of finish is the most important. This first coat is the seal coat will will soak in sealing the wood fibers, and unfortunately raise the grain causing it to feel rough and bumpy. Wood fibers are like straws and they soak up your finish, and when they do they swell creating rough spots and bumps. Any bumps and nibs will be sanded out smooth to create a nice foundation for the rest of the coats. Note that some finishes recommend that you apply a separate product for the seal coat.

Many light coats. The wood will soak up a lot of finish on the first coat, but don’t apply the finish too heavy. Many light coats are better than few heavy coats and you’re less likely to get runs, drips, and orange-peel. After the first coat you’ll notice that much less material is needed to coat the surface, and that the results get progressively smoother. Your raking light will help you see the finish get applied. Without a raking light, you’re more likely to apply heavy coats.

Wait before smoothing and recoating. Really, I know it feels dry and you have a deadline, but it may not be dry enough. If the manufacturer recommends four hours then you should wait four hours. Waiting means waiting, it doesn’t mean “go stir up dust in another part of the shop.”

Smooth between coats. I don’t like calling it sanding because people get too aggressive when I tell them to sand. The goal between coats is to smooth the finish and remove any nibs. Make sure you’ve let the finish dry completely, and go lightly. Do this by hand with a high grit (320) and and use finer grits as you move through coats. Go lightly. Wait, I already said that but it bears repeating. If your fingertips are white, you’re not sanding lightly.

Apply the recommended amount of coats. If the manufacturer recommends three coats, then apply no less than three coats.

Overtime

You still have some work to do. Let the piece go through the final cure while you do the following.

Clean the gun. Using the correct solvent for your finish, disassemble and clean your gun according to the manufacturer recommendation. If you used a water-based finish this can be done in the kitchen sink with warm soapy water, but spray alcohol through the gun and wipe everything down with alcohol as the last step. Water causes rust and you do not want a rusty gun. If you gun requires lubrication, do it. You might want a cleaning kit.

Write it down. For each piece, write down the finishing schedule which includes how you prepped the piece, the needle you chose, the fluid adjustment screw setting, the finish and how much it was diluted, the number of coats applied, drying times, the smoothing and polishing steps, and the wax used. If you are a professional tracking time and costs you may also want to include the time it took from start to end and amount of finished used.

The Finishing Touch

Congratulations! Your piece is done, now it’s time for the finishing touch.

Polish the surface. I don’t even want to call this smoothing, because you shouldn’t use sand paper. Using the finest synthetic steel wool pads which you can get here or here rub the surface to remove any nibs from the last coat. Again, go lightly.

Wax On, Wax Off. Divide the piece into sections and apply a good quality furniture wax to a section, wait for it to set up, and buff it out. Move onto the next section.

Fin. After reattaching any hardware and doing any final post-finishing assembly, you’re done!

Extra Credit

The tips above cover just the basic scenario of spraying a clear finish with an HVLP sprayer. There is so much to learn and know about finishing, and I’d love to see what you have to say in the comments below.

  • Using different finishing materials for different coats: for example applying oil as a first coat, moving to shellac for subsequent coats, and applying polyurethane as the final coat.
  • The different spray methods and their pros and cons: HVLP, conversion, gravity, LVLP, pressure pot, etc.
  • Spraying color: paints, tints, dyes, stains, and other pigments

Please share your tips or ask questions in the comments section.

7 thoughts on “Woodworker’s Spray Finishing Tips

  1. Todd A. Clippinger

    Ha! Funny I was just playing “The Fifth Element” in my shop while I worked last night!

    I use the 3M mask you listed and it works great. I have been using the 7500 series for years. They are comfortable and do a great job of sealing to the face if you get the right size.

    I am experienced in finishing and I think your entry is thorough and really hits on all the key issues of spraying in the shop.

  2. Shannon

    Outstanding post. I started compiling notes on this topic to do an episode with my Earlex this Spring as soon as I can open up the garage and ventilate better. Not sure I even have to at this point because you covered everything so well. I am still new to spraying as this is my first gun,so you covered several points I hadn’t thought of. Thanks for the extensive post!

  3. Matt Post author

    Thanks Shannon,
    I’ve only covered the most basic scenario – spraying clear finishes with HVLP. There is so much to learn about spraying, I think you should still do a post and look forward to reading it!

  4. TexWood

    Great Tips! I also believe you covered everything. While I have spayed some, this would make a good checklist for me to follow in the future.

    Thanks again

  5. Will Wilson

    Hi Matt,

    This was a great post! I feel like all I need to do now is “just add an Earlex” and I am good to go. Seriously, thank you for the excellent notes. I will definitely be putting a sprayer on my list of toys to add to the shop.

    At the seminar I went to they were saying water based finishes seem to not bring out the color of the wood so good. Do you finish with say Shellac first and then put on your water based finish? Any thoughts / strategies on that?

    -Will

  6. Matt Post author

    Hi Will,

    I have done a lot of hand rubbed finishes, and those can really bring out the color of the wood, and the dimension. I usually apply different materials for different coats when doing this. For example: one coat of danish oil, a few coats of shellac, then a oil-varnish topcoat. The danish oil soaks in, the shellac protects and dries fast so you can do lots of coats in one day, and the oil-varnish topcoat protects like shellac but doesn’t dissolve in alcohol.

    Water based finishes don’t usually showcase the color or dimension of the wood as good as the oil or solvent-based finishes. Many water based finishes can sit on the surface and look like you’ve laminated the piece with clear plastic. That’s not a look you want.

    However, Enduro Var is different. It really added depth to the maple on the fish tank stand and does not look plasticy. More on that in my next post.

    Thanks for stopping by the blog!

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